aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/ABI/stable/sysfs-driver-usb-usbtmc62
-rw-r--r--Documentation/ABI/testing/sysfs-bus-usb16
-rw-r--r--Documentation/ABI/testing/sysfs-bus-usb-devices-usbsevseg43
-rw-r--r--Documentation/DocBook/gadget.tmpl3
-rw-r--r--Documentation/DocBook/kernel-hacking.tmpl2
-rw-r--r--Documentation/MSI-HOWTO.txt6
-rw-r--r--Documentation/PCI/pci.txt4
-rw-r--r--Documentation/PCI/pcieaer-howto.txt11
-rw-r--r--Documentation/cgroups/cgroups.txt (renamed from Documentation/cgroups.txt)0
-rw-r--r--Documentation/cgroups/freezer-subsystem.txt99
-rw-r--r--Documentation/controllers/memory.txt24
-rw-r--r--Documentation/cpusets.txt2
-rw-r--r--Documentation/devices.txt3
-rw-r--r--Documentation/filesystems/ext3.txt5
-rw-r--r--Documentation/filesystems/ext4.txt32
-rw-r--r--Documentation/filesystems/proc.txt28
-rw-r--r--Documentation/filesystems/ubifs.txt9
-rw-r--r--Documentation/ioctl-number.txt3
-rw-r--r--Documentation/kernel-parameters.txt64
-rw-r--r--Documentation/markers.txt10
-rw-r--r--Documentation/mtd/nand_ecc.txt714
-rw-r--r--Documentation/sysrq.txt4
-rw-r--r--Documentation/tracepoints.txt101
-rw-r--r--Documentation/tracers/mmiotrace.txt5
-rw-r--r--Documentation/usb/anchors.txt17
-rw-r--r--Documentation/usb/misc_usbsevseg.txt46
-rw-r--r--Documentation/usb/power-management.txt8
-rw-r--r--Documentation/video4linux/CARDLIST.au08282
-rw-r--r--Documentation/video4linux/CARDLIST.tuner1
-rw-r--r--Documentation/vm/unevictable-lru.txt615
30 files changed, 1863 insertions, 76 deletions
diff --git a/Documentation/ABI/stable/sysfs-driver-usb-usbtmc b/Documentation/ABI/stable/sysfs-driver-usb-usbtmc
new file mode 100644
index 000000000000..9a75fb22187d
--- /dev/null
+++ b/Documentation/ABI/stable/sysfs-driver-usb-usbtmc
@@ -0,0 +1,62 @@
1What: /sys/bus/usb/drivers/usbtmc/devices/*/interface_capabilities
2What: /sys/bus/usb/drivers/usbtmc/devices/*/device_capabilities
3Date: August 2008
4Contact: Greg Kroah-Hartman <gregkh@suse.de>
5Description:
6 These files show the various USB TMC capabilities as described
7 by the device itself. The full description of the bitfields
8 can be found in the USB TMC documents from the USB-IF entitled
9 "Universal Serial Bus Test and Measurement Class Specification
10 (USBTMC) Revision 1.0" section 4.2.1.8.
11
12 The files are read only.
13
14
15What: /sys/bus/usb/drivers/usbtmc/devices/*/usb488_interface_capabilities
16What: /sys/bus/usb/drivers/usbtmc/devices/*/usb488_device_capabilities
17Date: August 2008
18Contact: Greg Kroah-Hartman <gregkh@suse.de>
19Description:
20 These files show the various USB TMC capabilities as described
21 by the device itself. The full description of the bitfields
22 can be found in the USB TMC documents from the USB-IF entitled
23 "Universal Serial Bus Test and Measurement Class, Subclass
24 USB488 Specification (USBTMC-USB488) Revision 1.0" section
25 4.2.2.
26
27 The files are read only.
28
29
30What: /sys/bus/usb/drivers/usbtmc/devices/*/TermChar
31Date: August 2008
32Contact: Greg Kroah-Hartman <gregkh@suse.de>
33Description:
34 This file is the TermChar value to be sent to the USB TMC
35 device as described by the document, "Universal Serial Bus Test
36 and Measurement Class Specification
37 (USBTMC) Revision 1.0" as published by the USB-IF.
38
39 Note that the TermCharEnabled file determines if this value is
40 sent to the device or not.
41
42
43What: /sys/bus/usb/drivers/usbtmc/devices/*/TermCharEnabled
44Date: August 2008
45Contact: Greg Kroah-Hartman <gregkh@suse.de>
46Description:
47 This file determines if the TermChar is to be sent to the
48 device on every transaction or not. For more details about
49 this, please see the document, "Universal Serial Bus Test and
50 Measurement Class Specification (USBTMC) Revision 1.0" as
51 published by the USB-IF.
52
53
54What: /sys/bus/usb/drivers/usbtmc/devices/*/auto_abort
55Date: August 2008
56Contact: Greg Kroah-Hartman <gregkh@suse.de>
57Description:
58 This file determines if the the transaction of the USB TMC
59 device is to be automatically aborted if there is any error.
60 For more details about this, please see the document,
61 "Universal Serial Bus Test and Measurement Class Specification
62 (USBTMC) Revision 1.0" as published by the USB-IF.
diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
index 11a3c1682cec..df6c8a0159f1 100644
--- a/Documentation/ABI/testing/sysfs-bus-usb
+++ b/Documentation/ABI/testing/sysfs-bus-usb
@@ -85,3 +85,19 @@ Description:
85Users: 85Users:
86 PowerTOP <power@bughost.org> 86 PowerTOP <power@bughost.org>
87 http://www.lesswatts.org/projects/powertop/ 87 http://www.lesswatts.org/projects/powertop/
88
89What: /sys/bus/usb/device/<busnum>-<devnum>...:<config num>-<interface num>/supports_autosuspend
90Date: January 2008
91KernelVersion: 2.6.27
92Contact: Sarah Sharp <sarah.a.sharp@intel.com>
93Description:
94 When read, this file returns 1 if the interface driver
95 for this interface supports autosuspend. It also
96 returns 1 if no driver has claimed this interface, as an
97 unclaimed interface will not stop the device from being
98 autosuspended if all other interface drivers are idle.
99 The file returns 0 if autosuspend support has not been
100 added to the driver.
101Users:
102 USB PM tool
103 git://git.moblin.org/users/sarah/usb-pm-tool/
diff --git a/Documentation/ABI/testing/sysfs-bus-usb-devices-usbsevseg b/Documentation/ABI/testing/sysfs-bus-usb-devices-usbsevseg
new file mode 100644
index 000000000000..cb830df8777c
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-usb-devices-usbsevseg
@@ -0,0 +1,43 @@
1Where: /sys/bus/usb/.../powered
2Date: August 2008
3Kernel Version: 2.6.26
4Contact: Harrison Metzger <harrisonmetz@gmail.com>
5Description: Controls whether the device's display will powered.
6 A value of 0 is off and a non-zero value is on.
7
8Where: /sys/bus/usb/.../mode_msb
9Where: /sys/bus/usb/.../mode_lsb
10Date: August 2008
11Kernel Version: 2.6.26
12Contact: Harrison Metzger <harrisonmetz@gmail.com>
13Description: Controls the devices display mode.
14 For a 6 character display the values are
15 MSB 0x06; LSB 0x3F, and
16 for an 8 character display the values are
17 MSB 0x08; LSB 0xFF.
18
19Where: /sys/bus/usb/.../textmode
20Date: August 2008
21Kernel Version: 2.6.26
22Contact: Harrison Metzger <harrisonmetz@gmail.com>
23Description: Controls the way the device interprets its text buffer.
24 raw: each character controls its segment manually
25 hex: each character is between 0-15
26 ascii: each character is between '0'-'9' and 'A'-'F'.
27
28Where: /sys/bus/usb/.../text
29Date: August 2008
30Kernel Version: 2.6.26
31Contact: Harrison Metzger <harrisonmetz@gmail.com>
32Description: The text (or data) for the device to display
33
34Where: /sys/bus/usb/.../decimals
35Date: August 2008
36Kernel Version: 2.6.26
37Contact: Harrison Metzger <harrisonmetz@gmail.com>
38Description: Controls the decimal places on the device.
39 To set the nth decimal place, give this field
40 the value of 10 ** n. Assume this field has
41 the value k and has 1 or more decimal places set,
42 to set the mth place (where m is not already set),
43 change this fields value to k + 10 ** m. \ No newline at end of file
diff --git a/Documentation/DocBook/gadget.tmpl b/Documentation/DocBook/gadget.tmpl
index ea3bc9565e6a..6ef2f0073e5a 100644
--- a/Documentation/DocBook/gadget.tmpl
+++ b/Documentation/DocBook/gadget.tmpl
@@ -557,6 +557,9 @@ Near-term plans include converting all of them, except for "gadgetfs".
557</para> 557</para>
558 558
559!Edrivers/usb/gadget/f_acm.c 559!Edrivers/usb/gadget/f_acm.c
560!Edrivers/usb/gadget/f_ecm.c
561!Edrivers/usb/gadget/f_subset.c
562!Edrivers/usb/gadget/f_obex.c
560!Edrivers/usb/gadget/f_serial.c 563!Edrivers/usb/gadget/f_serial.c
561 564
562</sect1> 565</sect1>
diff --git a/Documentation/DocBook/kernel-hacking.tmpl b/Documentation/DocBook/kernel-hacking.tmpl
index 4c63e5864160..ae15d55350ec 100644
--- a/Documentation/DocBook/kernel-hacking.tmpl
+++ b/Documentation/DocBook/kernel-hacking.tmpl
@@ -1105,7 +1105,7 @@ static struct block_device_operations opt_fops = {
1105 </listitem> 1105 </listitem>
1106 <listitem> 1106 <listitem>
1107 <para> 1107 <para>
1108 Function names as strings (__FUNCTION__). 1108 Function names as strings (__func__).
1109 </para> 1109 </para>
1110 </listitem> 1110 </listitem>
1111 <listitem> 1111 <listitem>
diff --git a/Documentation/MSI-HOWTO.txt b/Documentation/MSI-HOWTO.txt
index a51f693c1541..256defd7e174 100644
--- a/Documentation/MSI-HOWTO.txt
+++ b/Documentation/MSI-HOWTO.txt
@@ -236,10 +236,8 @@ software system can set different pages for controlling accesses to the
236MSI-X structure. The implementation of MSI support requires the PCI 236MSI-X structure. The implementation of MSI support requires the PCI
237subsystem, not a device driver, to maintain full control of the MSI-X 237subsystem, not a device driver, to maintain full control of the MSI-X
238table/MSI-X PBA (Pending Bit Array) and MMIO address space of the MSI-X 238table/MSI-X PBA (Pending Bit Array) and MMIO address space of the MSI-X
239table/MSI-X PBA. A device driver is prohibited from requesting the MMIO 239table/MSI-X PBA. A device driver should not access the MMIO address
240address space of the MSI-X table/MSI-X PBA. Otherwise, the PCI subsystem 240space of the MSI-X table/MSI-X PBA.
241will fail enabling MSI-X on its hardware device when it calls the function
242pci_enable_msix().
243 241
2445.3.2 API pci_enable_msix 2425.3.2 API pci_enable_msix
245 243
diff --git a/Documentation/PCI/pci.txt b/Documentation/PCI/pci.txt
index 8d4dc6250c58..fd4907a2968c 100644
--- a/Documentation/PCI/pci.txt
+++ b/Documentation/PCI/pci.txt
@@ -163,6 +163,10 @@ need pass only as many optional fields as necessary:
163 o class and classmask fields default to 0 163 o class and classmask fields default to 0
164 o driver_data defaults to 0UL. 164 o driver_data defaults to 0UL.
165 165
166Note that driver_data must match the value used by any of the pci_device_id
167entries defined in the driver. This makes the driver_data field mandatory
168if all the pci_device_id entries have a non-zero driver_data value.
169
166Once added, the driver probe routine will be invoked for any unclaimed 170Once added, the driver probe routine will be invoked for any unclaimed
167PCI devices listed in its (newly updated) pci_ids list. 171PCI devices listed in its (newly updated) pci_ids list.
168 172
diff --git a/Documentation/PCI/pcieaer-howto.txt b/Documentation/PCI/pcieaer-howto.txt
index 16c251230c82..ddeb14beacc8 100644
--- a/Documentation/PCI/pcieaer-howto.txt
+++ b/Documentation/PCI/pcieaer-howto.txt
@@ -203,22 +203,17 @@ to mmio_enabled.
203 203
2043.3 helper functions 2043.3 helper functions
205 205
2063.3.1 int pci_find_aer_capability(struct pci_dev *dev); 2063.3.1 int pci_enable_pcie_error_reporting(struct pci_dev *dev);
207pci_find_aer_capability locates the PCI Express AER capability
208in the device configuration space. If the device doesn't support
209PCI-Express AER, the function returns 0.
210
2113.3.2 int pci_enable_pcie_error_reporting(struct pci_dev *dev);
212pci_enable_pcie_error_reporting enables the device to send error 207pci_enable_pcie_error_reporting enables the device to send error
213messages to root port when an error is detected. Note that devices 208messages to root port when an error is detected. Note that devices
214don't enable the error reporting by default, so device drivers need 209don't enable the error reporting by default, so device drivers need
215call this function to enable it. 210call this function to enable it.
216 211
2173.3.3 int pci_disable_pcie_error_reporting(struct pci_dev *dev); 2123.3.2 int pci_disable_pcie_error_reporting(struct pci_dev *dev);
218pci_disable_pcie_error_reporting disables the device to send error 213pci_disable_pcie_error_reporting disables the device to send error
219messages to root port when an error is detected. 214messages to root port when an error is detected.
220 215
2213.3.4 int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev); 2163.3.3 int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev);
222pci_cleanup_aer_uncorrect_error_status cleanups the uncorrectable 217pci_cleanup_aer_uncorrect_error_status cleanups the uncorrectable
223error status register. 218error status register.
224 219
diff --git a/Documentation/cgroups.txt b/Documentation/cgroups/cgroups.txt
index d9014aa0eb68..d9014aa0eb68 100644
--- a/Documentation/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
diff --git a/Documentation/cgroups/freezer-subsystem.txt b/Documentation/cgroups/freezer-subsystem.txt
new file mode 100644
index 000000000000..c50ab58b72eb
--- /dev/null
+++ b/Documentation/cgroups/freezer-subsystem.txt
@@ -0,0 +1,99 @@
1 The cgroup freezer is useful to batch job management system which start
2and stop sets of tasks in order to schedule the resources of a machine
3according to the desires of a system administrator. This sort of program
4is often used on HPC clusters to schedule access to the cluster as a
5whole. The cgroup freezer uses cgroups to describe the set of tasks to
6be started/stopped by the batch job management system. It also provides
7a means to start and stop the tasks composing the job.
8
9 The cgroup freezer will also be useful for checkpointing running groups
10of tasks. The freezer allows the checkpoint code to obtain a consistent
11image of the tasks by attempting to force the tasks in a cgroup into a
12quiescent state. Once the tasks are quiescent another task can
13walk /proc or invoke a kernel interface to gather information about the
14quiesced tasks. Checkpointed tasks can be restarted later should a
15recoverable error occur. This also allows the checkpointed tasks to be
16migrated between nodes in a cluster by copying the gathered information
17to another node and restarting the tasks there.
18
19 Sequences of SIGSTOP and SIGCONT are not always sufficient for stopping
20and resuming tasks in userspace. Both of these signals are observable
21from within the tasks we wish to freeze. While SIGSTOP cannot be caught,
22blocked, or ignored it can be seen by waiting or ptracing parent tasks.
23SIGCONT is especially unsuitable since it can be caught by the task. Any
24programs designed to watch for SIGSTOP and SIGCONT could be broken by
25attempting to use SIGSTOP and SIGCONT to stop and resume tasks. We can
26demonstrate this problem using nested bash shells:
27
28 $ echo $$
29 16644
30 $ bash
31 $ echo $$
32 16690
33
34 From a second, unrelated bash shell:
35 $ kill -SIGSTOP 16690
36 $ kill -SIGCONT 16990
37
38 <at this point 16990 exits and causes 16644 to exit too>
39
40 This happens because bash can observe both signals and choose how it
41responds to them.
42
43 Another example of a program which catches and responds to these
44signals is gdb. In fact any program designed to use ptrace is likely to
45have a problem with this method of stopping and resuming tasks.
46
47 In contrast, the cgroup freezer uses the kernel freezer code to
48prevent the freeze/unfreeze cycle from becoming visible to the tasks
49being frozen. This allows the bash example above and gdb to run as
50expected.
51
52 The freezer subsystem in the container filesystem defines a file named
53freezer.state. Writing "FROZEN" to the state file will freeze all tasks in the
54cgroup. Subsequently writing "THAWED" will unfreeze the tasks in the cgroup.
55Reading will return the current state.
56
57* Examples of usage :
58
59 # mkdir /containers/freezer
60 # mount -t cgroup -ofreezer freezer /containers
61 # mkdir /containers/0
62 # echo $some_pid > /containers/0/tasks
63
64to get status of the freezer subsystem :
65
66 # cat /containers/0/freezer.state
67 THAWED
68
69to freeze all tasks in the container :
70
71 # echo FROZEN > /containers/0/freezer.state
72 # cat /containers/0/freezer.state
73 FREEZING
74 # cat /containers/0/freezer.state
75 FROZEN
76
77to unfreeze all tasks in the container :
78
79 # echo THAWED > /containers/0/freezer.state
80 # cat /containers/0/freezer.state
81 THAWED
82
83This is the basic mechanism which should do the right thing for user space task
84in a simple scenario.
85
86It's important to note that freezing can be incomplete. In that case we return
87EBUSY. This means that some tasks in the cgroup are busy doing something that
88prevents us from completely freezing the cgroup at this time. After EBUSY,
89the cgroup will remain partially frozen -- reflected by freezer.state reporting
90"FREEZING" when read. The state will remain "FREEZING" until one of these
91things happens:
92
93 1) Userspace cancels the freezing operation by writing "THAWED" to
94 the freezer.state file
95 2) Userspace retries the freezing operation by writing "FROZEN" to
96 the freezer.state file (writing "FREEZING" is not legal
97 and returns EIO)
98 3) The tasks that blocked the cgroup from entering the "FROZEN"
99 state disappear from the cgroup's set of tasks.
diff --git a/Documentation/controllers/memory.txt b/Documentation/controllers/memory.txt
index 9b53d5827361..1c07547d3f81 100644
--- a/Documentation/controllers/memory.txt
+++ b/Documentation/controllers/memory.txt
@@ -112,14 +112,22 @@ the per cgroup LRU.
112 112
1132.2.1 Accounting details 1132.2.1 Accounting details
114 114
115All mapped pages (RSS) and unmapped user pages (Page Cache) are accounted. 115All mapped anon pages (RSS) and cache pages (Page Cache) are accounted.
116RSS pages are accounted at the time of page_add_*_rmap() unless they've already 116(some pages which never be reclaimable and will not be on global LRU
117been accounted for earlier. A file page will be accounted for as Page Cache; 117 are not accounted. we just accounts pages under usual vm management.)
118it's mapped into the page tables of a process, duplicate accounting is carefully 118
119avoided. Page Cache pages are accounted at the time of add_to_page_cache(). 119RSS pages are accounted at page_fault unless they've already been accounted
120The corresponding routines that remove a page from the page tables or removes 120for earlier. A file page will be accounted for as Page Cache when it's
121a page from Page Cache is used to decrement the accounting counters of the 121inserted into inode (radix-tree). While it's mapped into the page tables of
122cgroup. 122processes, duplicate accounting is carefully avoided.
123
124A RSS page is unaccounted when it's fully unmapped. A PageCache page is
125unaccounted when it's removed from radix-tree.
126
127At page migration, accounting information is kept.
128
129Note: we just account pages-on-lru because our purpose is to control amount
130of used pages. not-on-lru pages are tend to be out-of-control from vm view.
123 131
1242.3 Shared Page Accounting 1322.3 Shared Page Accounting
125 133
diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt
index 47e568a9370a..5c86c258c791 100644
--- a/Documentation/cpusets.txt
+++ b/Documentation/cpusets.txt
@@ -48,7 +48,7 @@ hooks, beyond what is already present, required to manage dynamic
48job placement on large systems. 48job placement on large systems.
49 49
50Cpusets use the generic cgroup subsystem described in 50Cpusets use the generic cgroup subsystem described in
51Documentation/cgroup.txt. 51Documentation/cgroups/cgroups.txt.
52 52
53Requests by a task, using the sched_setaffinity(2) system call to 53Requests by a task, using the sched_setaffinity(2) system call to
54include CPUs in its CPU affinity mask, and using the mbind(2) and 54include CPUs in its CPU affinity mask, and using the mbind(2) and
diff --git a/Documentation/devices.txt b/Documentation/devices.txt
index 05c80645e4ee..2be08240ee80 100644
--- a/Documentation/devices.txt
+++ b/Documentation/devices.txt
@@ -2571,6 +2571,9 @@ Your cooperation is appreciated.
2571 160 = /dev/usb/legousbtower0 1st USB Legotower device 2571 160 = /dev/usb/legousbtower0 1st USB Legotower device
2572 ... 2572 ...
2573 175 = /dev/usb/legousbtower15 16th USB Legotower device 2573 175 = /dev/usb/legousbtower15 16th USB Legotower device
2574 176 = /dev/usb/usbtmc1 First USB TMC device
2575 ...
2576 192 = /dev/usb/usbtmc16 16th USB TMC device
2574 240 = /dev/usb/dabusb0 First daubusb device 2577 240 = /dev/usb/dabusb0 First daubusb device
2575 ... 2578 ...
2576 243 = /dev/usb/dabusb3 Fourth dabusb device 2579 243 = /dev/usb/dabusb3 Fourth dabusb device
diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt
index 295f26cd895a..9dd2a3bb2acc 100644
--- a/Documentation/filesystems/ext3.txt
+++ b/Documentation/filesystems/ext3.txt
@@ -96,6 +96,11 @@ errors=remount-ro(*) Remount the filesystem read-only on an error.
96errors=continue Keep going on a filesystem error. 96errors=continue Keep going on a filesystem error.
97errors=panic Panic and halt the machine if an error occurs. 97errors=panic Panic and halt the machine if an error occurs.
98 98
99data_err=ignore(*) Just print an error message if an error occurs
100 in a file data buffer in ordered mode.
101data_err=abort Abort the journal if an error occurs in a file
102 data buffer in ordered mode.
103
99grpid Give objects the same group ID as their creator. 104grpid Give objects the same group ID as their creator.
100bsdgroups 105bsdgroups
101 106
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index eb154ef36c2a..174eaff7ded9 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -2,19 +2,24 @@
2Ext4 Filesystem 2Ext4 Filesystem
3=============== 3===============
4 4
5This is a development version of the ext4 filesystem, an advanced level 5Ext4 is an an advanced level of the ext3 filesystem which incorporates
6of the ext3 filesystem which incorporates scalability and reliability 6scalability and reliability enhancements for supporting large filesystems
7enhancements for supporting large filesystems (64 bit) in keeping with 7(64 bit) in keeping with increasing disk capacities and state-of-the-art
8increasing disk capacities and state-of-the-art feature requirements. 8feature requirements.
9 9
10Mailing list: linux-ext4@vger.kernel.org 10Mailing list: linux-ext4@vger.kernel.org
11Web site: http://ext4.wiki.kernel.org
11 12
12 13
131. Quick usage instructions: 141. Quick usage instructions:
14=========================== 15===========================
15 16
17Note: More extensive information for getting started with ext4 can be
18 found at the ext4 wiki site at the URL:
19 http://ext4.wiki.kernel.org/index.php/Ext4_Howto
20
16 - Compile and install the latest version of e2fsprogs (as of this 21 - Compile and install the latest version of e2fsprogs (as of this
17 writing version 1.41) from: 22 writing version 1.41.3) from:
18 23
19 http://sourceforge.net/project/showfiles.php?group_id=2406 24 http://sourceforge.net/project/showfiles.php?group_id=2406
20 25
@@ -36,11 +41,9 @@ Mailing list: linux-ext4@vger.kernel.org
36 41
37 # mke2fs -t ext4 /dev/hda1 42 # mke2fs -t ext4 /dev/hda1
38 43
39 Or configure an existing ext3 filesystem to support extents and set 44 Or to configure an existing ext3 filesystem to support extents:
40 the test_fs flag to indicate that it's ok for an in-development
41 filesystem to touch this filesystem:
42 45
43 # tune2fs -O extents -E test_fs /dev/hda1 46 # tune2fs -O extents /dev/hda1
44 47
45 If the filesystem was created with 128 byte inodes, it can be 48 If the filesystem was created with 128 byte inodes, it can be
46 converted to use 256 byte for greater efficiency via: 49 converted to use 256 byte for greater efficiency via:
@@ -104,8 +107,8 @@ exist yet so I'm not sure they're in the near-term roadmap.
104The big performance win will come with mballoc, delalloc and flex_bg 107The big performance win will come with mballoc, delalloc and flex_bg
105grouping of bitmaps and inode tables. Some test results available here: 108grouping of bitmaps and inode tables. Some test results available here:
106 109
107 - http://www.bullopensource.org/ext4/20080530/ffsb-write-2.6.26-rc2.html 110 - http://www.bullopensource.org/ext4/20080818-ffsb/ffsb-write-2.6.27-rc1.html
108 - http://www.bullopensource.org/ext4/20080530/ffsb-readwrite-2.6.26-rc2.html 111 - http://www.bullopensource.org/ext4/20080818-ffsb/ffsb-readwrite-2.6.27-rc1.html
109 112
1103. Options 1133. Options
111========== 114==========
@@ -214,9 +217,6 @@ noreservation
214bsddf (*) Make 'df' act like BSD. 217bsddf (*) Make 'df' act like BSD.
215minixdf Make 'df' act like Minix. 218minixdf Make 'df' act like Minix.
216 219
217check=none Don't do extra checking of bitmaps on mount.
218nocheck
219
220debug Extra debugging information is sent to syslog. 220debug Extra debugging information is sent to syslog.
221 221
222errors=remount-ro(*) Remount the filesystem read-only on an error. 222errors=remount-ro(*) Remount the filesystem read-only on an error.
@@ -253,8 +253,6 @@ nobh (a) cache disk block mapping information
253 "nobh" option tries to avoid associating buffer 253 "nobh" option tries to avoid associating buffer
254 heads (supported only for "writeback" mode). 254 heads (supported only for "writeback" mode).
255 255
256mballoc (*) Use the multiple block allocator for block allocation
257nomballoc disabled multiple block allocator for block allocation.
258stripe=n Number of filesystem blocks that mballoc will try 256stripe=n Number of filesystem blocks that mballoc will try
259 to use for allocation size and alignment. For RAID5/6 257 to use for allocation size and alignment. For RAID5/6
260 systems this should be the number of data 258 systems this should be the number of data
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index c032bf39e8b9..bcceb99b81dd 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -1384,15 +1384,18 @@ causes the kernel to prefer to reclaim dentries and inodes.
1384dirty_background_ratio 1384dirty_background_ratio
1385---------------------- 1385----------------------
1386 1386
1387Contains, as a percentage of total system memory, the number of pages at which 1387Contains, as a percentage of the dirtyable system memory (free pages + mapped
1388the pdflush background writeback daemon will start writing out dirty data. 1388pages + file cache, not including locked pages and HugePages), the number of
1389pages at which the pdflush background writeback daemon will start writing out
1390dirty data.
1389 1391
1390dirty_ratio 1392dirty_ratio
1391----------------- 1393-----------------
1392 1394
1393Contains, as a percentage of total system memory, the number of pages at which 1395Contains, as a percentage of the dirtyable system memory (free pages + mapped
1394a process which is generating disk writes will itself start writing out dirty 1396pages + file cache, not including locked pages and HugePages), the number of
1395data. 1397pages at which a process which is generating disk writes will itself start
1398writing out dirty data.
1396 1399
1397dirty_writeback_centisecs 1400dirty_writeback_centisecs
1398------------------------- 1401-------------------------
@@ -2412,24 +2415,29 @@ will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
2412of memory types. If a bit of the bitmask is set, memory segments of the 2415of memory types. If a bit of the bitmask is set, memory segments of the
2413corresponding memory type are dumped, otherwise they are not dumped. 2416corresponding memory type are dumped, otherwise they are not dumped.
2414 2417
2415The following 4 memory types are supported: 2418The following 7 memory types are supported:
2416 - (bit 0) anonymous private memory 2419 - (bit 0) anonymous private memory
2417 - (bit 1) anonymous shared memory 2420 - (bit 1) anonymous shared memory
2418 - (bit 2) file-backed private memory 2421 - (bit 2) file-backed private memory
2419 - (bit 3) file-backed shared memory 2422 - (bit 3) file-backed shared memory
2420 - (bit 4) ELF header pages in file-backed private memory areas (it is 2423 - (bit 4) ELF header pages in file-backed private memory areas (it is
2421 effective only if the bit 2 is cleared) 2424 effective only if the bit 2 is cleared)
2425 - (bit 5) hugetlb private memory
2426 - (bit 6) hugetlb shared memory
2422 2427
2423 Note that MMIO pages such as frame buffer are never dumped and vDSO pages 2428 Note that MMIO pages such as frame buffer are never dumped and vDSO pages
2424 are always dumped regardless of the bitmask status. 2429 are always dumped regardless of the bitmask status.
2425 2430
2426Default value of coredump_filter is 0x3; this means all anonymous memory 2431 Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only
2427segments are dumped. 2432 effected by bit 5-6.
2433
2434Default value of coredump_filter is 0x23; this means all anonymous memory
2435segments and hugetlb private memory are dumped.
2428 2436
2429If you don't want to dump all shared memory segments attached to pid 1234, 2437If you don't want to dump all shared memory segments attached to pid 1234,
2430write 1 to the process's proc file. 2438write 0x21 to the process's proc file.
2431 2439
2432 $ echo 0x1 > /proc/1234/coredump_filter 2440 $ echo 0x21 > /proc/1234/coredump_filter
2433 2441
2434When a new process is created, the process inherits the bitmask status from its 2442When a new process is created, the process inherits the bitmask status from its
2435parent. It is useful to set up coredump_filter before the program runs. 2443parent. It is useful to set up coredump_filter before the program runs.
diff --git a/Documentation/filesystems/ubifs.txt b/Documentation/filesystems/ubifs.txt
index 6a0d70a22f05..dd84ea3c10da 100644
--- a/Documentation/filesystems/ubifs.txt
+++ b/Documentation/filesystems/ubifs.txt
@@ -86,6 +86,15 @@ norm_unmount (*) commit on unmount; the journal is committed
86fast_unmount do not commit on unmount; this option makes 86fast_unmount do not commit on unmount; this option makes
87 unmount faster, but the next mount slower 87 unmount faster, but the next mount slower
88 because of the need to replay the journal. 88 because of the need to replay the journal.
89bulk_read read more in one go to take advantage of flash
90 media that read faster sequentially
91no_bulk_read (*) do not bulk-read
92no_chk_data_crc skip checking of CRCs on data nodes in order to
93 improve read performance. Use this option only
94 if the flash media is highly reliable. The effect
95 of this option is that corruption of the contents
96 of a file can go unnoticed.
97chk_data_crc (*) do not skip checking CRCs on data nodes
89 98
90 99
91Quick usage instructions 100Quick usage instructions
diff --git a/Documentation/ioctl-number.txt b/Documentation/ioctl-number.txt
index 1c6b545635a2..b880ce5dbd33 100644
--- a/Documentation/ioctl-number.txt
+++ b/Documentation/ioctl-number.txt
@@ -92,6 +92,7 @@ Code Seq# Include File Comments
92'J' 00-1F drivers/scsi/gdth_ioctl.h 92'J' 00-1F drivers/scsi/gdth_ioctl.h
93'K' all linux/kd.h 93'K' all linux/kd.h
94'L' 00-1F linux/loop.h 94'L' 00-1F linux/loop.h
95'L' 20-2F driver/usb/misc/vstusb.h
95'L' E0-FF linux/ppdd.h encrypted disk device driver 96'L' E0-FF linux/ppdd.h encrypted disk device driver
96 <http://linux01.gwdg.de/~alatham/ppdd.html> 97 <http://linux01.gwdg.de/~alatham/ppdd.html>
97'M' all linux/soundcard.h 98'M' all linux/soundcard.h
@@ -110,6 +111,8 @@ Code Seq# Include File Comments
110'W' 00-1F linux/wanrouter.h conflict! 111'W' 00-1F linux/wanrouter.h conflict!
111'X' all linux/xfs_fs.h 112'X' all linux/xfs_fs.h
112'Y' all linux/cyclades.h 113'Y' all linux/cyclades.h
114'[' 00-07 linux/usb/usbtmc.h USB Test and Measurement Devices
115 <mailto:gregkh@suse.de>
113'a' all ATM on linux 116'a' all ATM on linux
114 <http://lrcwww.epfl.ch/linux-atm/magic.html> 117 <http://lrcwww.epfl.ch/linux-atm/magic.html>
115'b' 00-FF bit3 vme host bridge 118'b' 00-FF bit3 vme host bridge
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index dd28a0d56981..53ba7c7d82b3 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -101,6 +101,7 @@ parameter is applicable:
101 X86-64 X86-64 architecture is enabled. 101 X86-64 X86-64 architecture is enabled.
102 More X86-64 boot options can be found in 102 More X86-64 boot options can be found in
103 Documentation/x86_64/boot-options.txt . 103 Documentation/x86_64/boot-options.txt .
104 X86 Either 32bit or 64bit x86 (same as X86-32+X86-64)
104 105
105In addition, the following text indicates that the option: 106In addition, the following text indicates that the option:
106 107
@@ -690,7 +691,7 @@ and is between 256 and 4096 characters. It is defined in the file
690 See Documentation/block/as-iosched.txt and 691 See Documentation/block/as-iosched.txt and
691 Documentation/block/deadline-iosched.txt for details. 692 Documentation/block/deadline-iosched.txt for details.
692 693
693 elfcorehdr= [X86-32, X86_64] 694 elfcorehdr= [IA64,PPC,SH,X86-32,X86_64]
694 Specifies physical address of start of kernel core 695 Specifies physical address of start of kernel core
695 image elf header. Generally kexec loader will 696 image elf header. Generally kexec loader will
696 pass this option to capture kernel. 697 pass this option to capture kernel.
@@ -796,6 +797,8 @@ and is between 256 and 4096 characters. It is defined in the file
796 Defaults to the default architecture's huge page size 797 Defaults to the default architecture's huge page size
797 if not specified. 798 if not specified.
798 799
800 hlt [BUGS=ARM,SH]
801
799 i8042.debug [HW] Toggle i8042 debug mode 802 i8042.debug [HW] Toggle i8042 debug mode
800 i8042.direct [HW] Put keyboard port into non-translated mode 803 i8042.direct [HW] Put keyboard port into non-translated mode
801 i8042.dumbkbd [HW] Pretend that controller can only read data from 804 i8042.dumbkbd [HW] Pretend that controller can only read data from
@@ -1211,6 +1214,10 @@ and is between 256 and 4096 characters. It is defined in the file
1211 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 1214 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1212 memory. 1215 memory.
1213 1216
1217 memchunk=nn[KMG]
1218 [KNL,SH] Allow user to override the default size for
1219 per-device physically contiguous DMA buffers.
1220
1214 memmap=exactmap [KNL,X86-32,X86_64] Enable setting of an exact 1221 memmap=exactmap [KNL,X86-32,X86_64] Enable setting of an exact
1215 E820 memory map, as specified by the user. 1222 E820 memory map, as specified by the user.
1216 Such memmap=exactmap lines can be constructed based on 1223 Such memmap=exactmap lines can be constructed based on
@@ -1393,6 +1400,8 @@ and is between 256 and 4096 characters. It is defined in the file
1393 1400
1394 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects. 1401 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1395 1402
1403 nodsp [SH] Disable hardware DSP at boot time.
1404
1396 noefi [X86-32,X86-64] Disable EFI runtime services support. 1405 noefi [X86-32,X86-64] Disable EFI runtime services support.
1397 1406
1398 noexec [IA-64] 1407 noexec [IA-64]
@@ -1409,13 +1418,15 @@ and is between 256 and 4096 characters. It is defined in the file
1409 noexec32=off: disable non-executable mappings 1418 noexec32=off: disable non-executable mappings
1410 read implies executable mappings 1419 read implies executable mappings
1411 1420
1421 nofpu [SH] Disable hardware FPU at boot time.
1422
1412 nofxsr [BUGS=X86-32] Disables x86 floating point extended 1423 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1413 register save and restore. The kernel will only save 1424 register save and restore. The kernel will only save
1414 legacy floating-point registers on task switch. 1425 legacy floating-point registers on task switch.
1415 1426
1416 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 1427 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1417 1428
1418 nohlt [BUGS=ARM] 1429 nohlt [BUGS=ARM,SH]
1419 1430
1420 no-hlt [BUGS=X86-32] Tells the kernel that the hlt 1431 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1421 instruction doesn't work correctly and not to 1432 instruction doesn't work correctly and not to
@@ -1578,7 +1589,7 @@ and is between 256 and 4096 characters. It is defined in the file
1578 See also Documentation/paride.txt. 1589 See also Documentation/paride.txt.
1579 1590
1580 pci=option[,option...] [PCI] various PCI subsystem options: 1591 pci=option[,option...] [PCI] various PCI subsystem options:
1581 off [X86-32] don't probe for the PCI bus 1592 off [X86] don't probe for the PCI bus
1582 bios [X86-32] force use of PCI BIOS, don't access 1593 bios [X86-32] force use of PCI BIOS, don't access
1583 the hardware directly. Use this if your machine 1594 the hardware directly. Use this if your machine
1584 has a non-standard PCI host bridge. 1595 has a non-standard PCI host bridge.
@@ -1586,9 +1597,9 @@ and is between 256 and 4096 characters. It is defined in the file
1586 hardware access methods are allowed. Use this 1597 hardware access methods are allowed. Use this
1587 if you experience crashes upon bootup and you 1598 if you experience crashes upon bootup and you
1588 suspect they are caused by the BIOS. 1599 suspect they are caused by the BIOS.
1589 conf1 [X86-32] Force use of PCI Configuration 1600 conf1 [X86] Force use of PCI Configuration
1590 Mechanism 1. 1601 Mechanism 1.
1591 conf2 [X86-32] Force use of PCI Configuration 1602 conf2 [X86] Force use of PCI Configuration
1592 Mechanism 2. 1603 Mechanism 2.
1593 noaer [PCIE] If the PCIEAER kernel config parameter is 1604 noaer [PCIE] If the PCIEAER kernel config parameter is
1594 enabled, this kernel boot option can be used to 1605 enabled, this kernel boot option can be used to
@@ -1608,37 +1619,37 @@ and is between 256 and 4096 characters. It is defined in the file
1608 this option if the kernel is unable to allocate 1619 this option if the kernel is unable to allocate
1609 IRQs or discover secondary PCI buses on your 1620 IRQs or discover secondary PCI buses on your
1610 motherboard. 1621 motherboard.
1611 rom [X86-32] Assign address space to expansion ROMs. 1622 rom [X86] Assign address space to expansion ROMs.
1612 Use with caution as certain devices share 1623 Use with caution as certain devices share
1613 address decoders between ROMs and other 1624 address decoders between ROMs and other
1614 resources. 1625 resources.
1615 norom [X86-32,X86_64] Do not assign address space to 1626 norom [X86] Do not assign address space to
1616 expansion ROMs that do not already have 1627 expansion ROMs that do not already have
1617 BIOS assigned address ranges. 1628 BIOS assigned address ranges.
1618 irqmask=0xMMMM [X86-32] Set a bit mask of IRQs allowed to be 1629 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
1619 assigned automatically to PCI devices. You can 1630 assigned automatically to PCI devices. You can
1620 make the kernel exclude IRQs of your ISA cards 1631 make the kernel exclude IRQs of your ISA cards
1621 this way. 1632 this way.
1622 pirqaddr=0xAAAAA [X86-32] Specify the physical address 1633 pirqaddr=0xAAAAA [X86] Specify the physical address
1623 of the PIRQ table (normally generated 1634 of the PIRQ table (normally generated
1624 by the BIOS) if it is outside the 1635 by the BIOS) if it is outside the
1625 F0000h-100000h range. 1636 F0000h-100000h range.
1626 lastbus=N [X86-32] Scan all buses thru bus #N. Can be 1637 lastbus=N [X86] Scan all buses thru bus #N. Can be
1627 useful if the kernel is unable to find your 1638 useful if the kernel is unable to find your
1628 secondary buses and you want to tell it 1639 secondary buses and you want to tell it
1629 explicitly which ones they are. 1640 explicitly which ones they are.
1630 assign-busses [X86-32] Always assign all PCI bus 1641 assign-busses [X86] Always assign all PCI bus
1631 numbers ourselves, overriding 1642 numbers ourselves, overriding
1632 whatever the firmware may have done. 1643 whatever the firmware may have done.
1633 usepirqmask [X86-32] Honor the possible IRQ mask stored 1644 usepirqmask [X86] Honor the possible IRQ mask stored
1634 in the BIOS $PIR table. This is needed on 1645 in the BIOS $PIR table. This is needed on
1635 some systems with broken BIOSes, notably 1646 some systems with broken BIOSes, notably
1636 some HP Pavilion N5400 and Omnibook XE3 1647 some HP Pavilion N5400 and Omnibook XE3
1637 notebooks. This will have no effect if ACPI 1648 notebooks. This will have no effect if ACPI
1638 IRQ routing is enabled. 1649 IRQ routing is enabled.
1639 noacpi [X86-32] Do not use ACPI for IRQ routing 1650 noacpi [X86] Do not use ACPI for IRQ routing
1640 or for PCI scanning. 1651 or for PCI scanning.
1641 use_crs [X86-32] Use _CRS for PCI resource 1652 use_crs [X86] Use _CRS for PCI resource
1642 allocation. 1653 allocation.
1643 routeirq Do IRQ routing for all PCI devices. 1654 routeirq Do IRQ routing for all PCI devices.
1644 This is normally done in pci_enable_device(), 1655 This is normally done in pci_enable_device(),
@@ -1667,6 +1678,12 @@ and is between 256 and 4096 characters. It is defined in the file
1667 reserved for the CardBus bridge's memory 1678 reserved for the CardBus bridge's memory
1668 window. The default value is 64 megabytes. 1679 window. The default value is 64 megabytes.
1669 1680
1681 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
1682 Management.
1683 off Disable ASPM.
1684 force Enable ASPM even on devices that claim not to support it.
1685 WARNING: Forcing ASPM on may cause system lockups.
1686
1670 pcmv= [HW,PCMCIA] BadgePAD 4 1687 pcmv= [HW,PCMCIA] BadgePAD 4
1671 1688
1672 pd. [PARIDE] 1689 pd. [PARIDE]
@@ -2253,6 +2270,25 @@ and is between 256 and 4096 characters. It is defined in the file
2253 autosuspended. Devices for which the delay is set 2270 autosuspended. Devices for which the delay is set
2254 to a negative value won't be autosuspended at all. 2271 to a negative value won't be autosuspended at all.
2255 2272
2273 usbcore.usbfs_snoop=
2274 [USB] Set to log all usbfs traffic (default 0 = off).
2275
2276 usbcore.blinkenlights=
2277 [USB] Set to cycle leds on hubs (default 0 = off).
2278
2279 usbcore.old_scheme_first=
2280 [USB] Start with the old device initialization
2281 scheme (default 0 = off).
2282
2283 usbcore.use_both_schemes=
2284 [USB] Try the other device initialization scheme
2285 if the first one fails (default 1 = enabled).
2286
2287 usbcore.initial_descriptor_timeout=
2288 [USB] Specifies timeout for the initial 64-byte
2289 USB_REQ_GET_DESCRIPTOR request in milliseconds
2290 (default 5000 = 5.0 seconds).
2291
2256 usbhid.mousepoll= 2292 usbhid.mousepoll=
2257 [USBHID] The interval which mice are to be polled at. 2293 [USBHID] The interval which mice are to be polled at.
2258 2294
diff --git a/Documentation/markers.txt b/Documentation/markers.txt
index d9f50a19fa0c..089f6138fcd9 100644
--- a/Documentation/markers.txt
+++ b/Documentation/markers.txt
@@ -50,10 +50,12 @@ Connecting a function (probe) to a marker is done by providing a probe (function
50to call) for the specific marker through marker_probe_register() and can be 50to call) for the specific marker through marker_probe_register() and can be
51activated by calling marker_arm(). Marker deactivation can be done by calling 51activated by calling marker_arm(). Marker deactivation can be done by calling
52marker_disarm() as many times as marker_arm() has been called. Removing a probe 52marker_disarm() as many times as marker_arm() has been called. Removing a probe
53is done through marker_probe_unregister(); it will disarm the probe and make 53is done through marker_probe_unregister(); it will disarm the probe.
54sure there is no caller left using the probe when it returns. Probe removal is 54marker_synchronize_unregister() must be called before the end of the module exit
55preempt-safe because preemption is disabled around the probe call. See the 55function to make sure there is no caller left using the probe. This, and the
56"Probe example" section below for a sample probe module. 56fact that preemption is disabled around the probe call, make sure that probe
57removal and module unload are safe. See the "Probe example" section below for a
58sample probe module.
57 59
58The marker mechanism supports inserting multiple instances of the same marker. 60The marker mechanism supports inserting multiple instances of the same marker.
59Markers can be put in inline functions, inlined static functions, and 61Markers can be put in inline functions, inlined static functions, and
diff --git a/Documentation/mtd/nand_ecc.txt b/Documentation/mtd/nand_ecc.txt
new file mode 100644
index 000000000000..bdf93b7f0f24
--- /dev/null
+++ b/Documentation/mtd/nand_ecc.txt
@@ -0,0 +1,714 @@
1Introduction
2============
3
4Having looked at the linux mtd/nand driver and more specific at nand_ecc.c
5I felt there was room for optimisation. I bashed the code for a few hours
6performing tricks like table lookup removing superfluous code etc.
7After that the speed was increased by 35-40%.
8Still I was not too happy as I felt there was additional room for improvement.
9
10Bad! I was hooked.
11I decided to annotate my steps in this file. Perhaps it is useful to someone
12or someone learns something from it.
13
14
15The problem
16===========
17
18NAND flash (at least SLC one) typically has sectors of 256 bytes.
19However NAND flash is not extremely reliable so some error detection
20(and sometimes correction) is needed.
21
22This is done by means of a Hamming code. I'll try to explain it in
23laymans terms (and apologies to all the pro's in the field in case I do
24not use the right terminology, my coding theory class was almost 30
25years ago, and I must admit it was not one of my favourites).
26
27As I said before the ecc calculation is performed on sectors of 256
28bytes. This is done by calculating several parity bits over the rows and
29columns. The parity used is even parity which means that the parity bit = 1
30if the data over which the parity is calculated is 1 and the parity bit = 0
31if the data over which the parity is calculated is 0. So the total
32number of bits over the data over which the parity is calculated + the
33parity bit is even. (see wikipedia if you can't follow this).
34Parity is often calculated by means of an exclusive or operation,
35sometimes also referred to as xor. In C the operator for xor is ^
36
37Back to ecc.
38Let's give a small figure:
39
40byte 0: bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 rp0 rp2 rp4 ... rp14
41byte 1: bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 rp1 rp2 rp4 ... rp14
42byte 2: bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 rp0 rp3 rp4 ... rp14
43byte 3: bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 rp1 rp3 rp4 ... rp14
44byte 4: bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 rp0 rp2 rp5 ... rp14
45....
46byte 254: bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 rp0 rp3 rp5 ... rp15
47byte 255: bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 rp1 rp3 rp5 ... rp15
48 cp1 cp0 cp1 cp0 cp1 cp0 cp1 cp0
49 cp3 cp3 cp2 cp2 cp3 cp3 cp2 cp2
50 cp5 cp5 cp5 cp5 cp4 cp4 cp4 cp4
51
52This figure represents a sector of 256 bytes.
53cp is my abbreviaton for column parity, rp for row parity.
54
55Let's start to explain column parity.
56cp0 is the parity that belongs to all bit0, bit2, bit4, bit6.
57so the sum of all bit0, bit2, bit4 and bit6 values + cp0 itself is even.
58Similarly cp1 is the sum of all bit1, bit3, bit5 and bit7.
59cp2 is the parity over bit0, bit1, bit4 and bit5
60cp3 is the parity over bit2, bit3, bit6 and bit7.
61cp4 is the parity over bit0, bit1, bit2 and bit3.
62cp5 is the parity over bit4, bit5, bit6 and bit7.
63Note that each of cp0 .. cp5 is exactly one bit.
64
65Row parity actually works almost the same.
66rp0 is the parity of all even bytes (0, 2, 4, 6, ... 252, 254)
67rp1 is the parity of all odd bytes (1, 3, 5, 7, ..., 253, 255)
68rp2 is the parity of all bytes 0, 1, 4, 5, 8, 9, ...
69(so handle two bytes, then skip 2 bytes).
70rp3 is covers the half rp2 does not cover (bytes 2, 3, 6, 7, 10, 11, ...)
71for rp4 the rule is cover 4 bytes, skip 4 bytes, cover 4 bytes, skip 4 etc.
72so rp4 calculates parity over bytes 0, 1, 2, 3, 8, 9, 10, 11, 16, ...)
73and rp5 covers the other half, so bytes 4, 5, 6, 7, 12, 13, 14, 15, 20, ..
74The story now becomes quite boring. I guess you get the idea.
75rp6 covers 8 bytes then skips 8 etc
76rp7 skips 8 bytes then covers 8 etc
77rp8 covers 16 bytes then skips 16 etc
78rp9 skips 16 bytes then covers 16 etc
79rp10 covers 32 bytes then skips 32 etc
80rp11 skips 32 bytes then covers 32 etc
81rp12 covers 64 bytes then skips 64 etc
82rp13 skips 64 bytes then covers 64 etc
83rp14 covers 128 bytes then skips 128
84rp15 skips 128 bytes then covers 128
85
86In the end the parity bits are grouped together in three bytes as
87follows:
88ECC Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
89ECC 0 rp07 rp06 rp05 rp04 rp03 rp02 rp01 rp00
90ECC 1 rp15 rp14 rp13 rp12 rp11 rp10 rp09 rp08
91ECC 2 cp5 cp4 cp3 cp2 cp1 cp0 1 1
92
93I detected after writing this that ST application note AN1823
94(http://www.st.com/stonline/books/pdf/docs/10123.pdf) gives a much
95nicer picture.(but they use line parity as term where I use row parity)
96Oh well, I'm graphically challenged, so suffer with me for a moment :-)
97And I could not reuse the ST picture anyway for copyright reasons.
98
99
100Attempt 0
101=========
102
103Implementing the parity calculation is pretty simple.
104In C pseudocode:
105for (i = 0; i < 256; i++)
106{
107 if (i & 0x01)
108 rp1 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp1;
109 else
110 rp0 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp1;
111 if (i & 0x02)
112 rp3 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp3;
113 else
114 rp2 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp2;
115 if (i & 0x04)
116 rp5 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp5;
117 else
118 rp4 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp4;
119 if (i & 0x08)
120 rp7 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp7;
121 else
122 rp6 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp6;
123 if (i & 0x10)
124 rp9 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp9;
125 else
126 rp8 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp8;
127 if (i & 0x20)
128 rp11 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp11;
129 else
130 rp10 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp10;
131 if (i & 0x40)
132 rp13 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp13;
133 else
134 rp12 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp12;
135 if (i & 0x80)
136 rp15 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp15;
137 else
138 rp14 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ bit3 ^ bit2 ^ bit1 ^ bit0 ^ rp14;
139 cp0 = bit6 ^ bit4 ^ bit2 ^ bit0 ^ cp0;
140 cp1 = bit7 ^ bit5 ^ bit3 ^ bit1 ^ cp1;
141 cp2 = bit5 ^ bit4 ^ bit1 ^ bit0 ^ cp2;
142 cp3 = bit7 ^ bit6 ^ bit3 ^ bit2 ^ cp3
143 cp4 = bit3 ^ bit2 ^ bit1 ^ bit0 ^ cp4
144 cp5 = bit7 ^ bit6 ^ bit5 ^ bit4 ^ cp5
145}
146
147
148Analysis 0
149==========
150
151C does have bitwise operators but not really operators to do the above
152efficiently (and most hardware has no such instructions either).
153Therefore without implementing this it was clear that the code above was
154not going to bring me a Nobel prize :-)
155
156Fortunately the exclusive or operation is commutative, so we can combine
157the values in any order. So instead of calculating all the bits
158individually, let us try to rearrange things.
159For the column parity this is easy. We can just xor the bytes and in the
160end filter out the relevant bits. This is pretty nice as it will bring
161all cp calculation out of the if loop.
162
163Similarly we can first xor the bytes for the various rows.
164This leads to:
165
166
167Attempt 1
168=========
169
170const char parity[256] = {
171 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
172 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
173 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
174 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
175 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
176 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
177 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
178 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
179 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
180 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
181 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
182 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
183 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
184 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
185 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
186 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0
187};
188
189void ecc1(const unsigned char *buf, unsigned char *code)
190{
191 int i;
192 const unsigned char *bp = buf;
193 unsigned char cur;
194 unsigned char rp0, rp1, rp2, rp3, rp4, rp5, rp6, rp7;
195 unsigned char rp8, rp9, rp10, rp11, rp12, rp13, rp14, rp15;
196 unsigned char par;
197
198 par = 0;
199 rp0 = 0; rp1 = 0; rp2 = 0; rp3 = 0;
200 rp4 = 0; rp5 = 0; rp6 = 0; rp7 = 0;
201 rp8 = 0; rp9 = 0; rp10 = 0; rp11 = 0;
202 rp12 = 0; rp13 = 0; rp14 = 0; rp15 = 0;
203
204 for (i = 0; i < 256; i++)
205 {
206 cur = *bp++;
207 par ^= cur;
208 if (i & 0x01) rp1 ^= cur; else rp0 ^= cur;
209 if (i & 0x02) rp3 ^= cur; else rp2 ^= cur;
210 if (i & 0x04) rp5 ^= cur; else rp4 ^= cur;
211 if (i & 0x08) rp7 ^= cur; else rp6 ^= cur;
212 if (i & 0x10) rp9 ^= cur; else rp8 ^= cur;
213 if (i & 0x20) rp11 ^= cur; else rp10 ^= cur;
214 if (i & 0x40) rp13 ^= cur; else rp12 ^= cur;
215 if (i & 0x80) rp15 ^= cur; else rp14 ^= cur;
216 }
217 code[0] =
218 (parity[rp7] << 7) |
219 (parity[rp6] << 6) |
220 (parity[rp5] << 5) |
221 (parity[rp4] << 4) |
222 (parity[rp3] << 3) |
223 (parity[rp2] << 2) |
224 (parity[rp1] << 1) |
225 (parity[rp0]);
226 code[1] =
227 (parity[rp15] << 7) |
228 (parity[rp14] << 6) |
229 (parity[rp13] << 5) |
230 (parity[rp12] << 4) |
231 (parity[rp11] << 3) |
232 (parity[rp10] << 2) |
233 (parity[rp9] << 1) |
234 (parity[rp8]);
235 code[2] =
236 (parity[par & 0xf0] << 7) |
237 (parity[par & 0x0f] << 6) |
238 (parity[par & 0xcc] << 5) |
239 (parity[par & 0x33] << 4) |
240 (parity[par & 0xaa] << 3) |
241 (parity[par & 0x55] << 2);
242 code[0] = ~code[0];
243 code[1] = ~code[1];
244 code[2] = ~code[2];
245}
246
247Still pretty straightforward. The last three invert statements are there to
248give a checksum of 0xff 0xff 0xff for an empty flash. In an empty flash
249all data is 0xff, so the checksum then matches.
250
251I also introduced the parity lookup. I expected this to be the fastest
252way to calculate the parity, but I will investigate alternatives later
253on.
254
255
256Analysis 1
257==========
258
259The code works, but is not terribly efficient. On my system it took
260almost 4 times as much time as the linux driver code. But hey, if it was
261*that* easy this would have been done long before.
262No pain. no gain.
263
264Fortunately there is plenty of room for improvement.
265
266In step 1 we moved from bit-wise calculation to byte-wise calculation.
267However in C we can also use the unsigned long data type and virtually
268every modern microprocessor supports 32 bit operations, so why not try
269to write our code in such a way that we process data in 32 bit chunks.
270
271Of course this means some modification as the row parity is byte by
272byte. A quick analysis:
273for the column parity we use the par variable. When extending to 32 bits
274we can in the end easily calculate p0 and p1 from it.
275(because par now consists of 4 bytes, contributing to rp1, rp0, rp1, rp0
276respectively)
277also rp2 and rp3 can be easily retrieved from par as rp3 covers the
278first two bytes and rp2 the last two bytes.
279
280Note that of course now the loop is executed only 64 times (256/4).
281And note that care must taken wrt byte ordering. The way bytes are
282ordered in a long is machine dependent, and might affect us.
283Anyway, if there is an issue: this code is developed on x86 (to be
284precise: a DELL PC with a D920 Intel CPU)
285
286And of course the performance might depend on alignment, but I expect
287that the I/O buffers in the nand driver are aligned properly (and
288otherwise that should be fixed to get maximum performance).
289
290Let's give it a try...
291
292
293Attempt 2
294=========
295
296extern const char parity[256];
297
298void ecc2(const unsigned char *buf, unsigned char *code)
299{
300 int i;
301 const unsigned long *bp = (unsigned long *)buf;
302 unsigned long cur;
303 unsigned long rp0, rp1, rp2, rp3, rp4, rp5, rp6, rp7;
304 unsigned long rp8, rp9, rp10, rp11, rp12, rp13, rp14, rp15;
305 unsigned long par;
306
307 par = 0;
308 rp0 = 0; rp1 = 0; rp2 = 0; rp3 = 0;
309 rp4 = 0; rp5 = 0; rp6 = 0; rp7 = 0;
310 rp8 = 0; rp9 = 0; rp10 = 0; rp11 = 0;
311 rp12 = 0; rp13 = 0; rp14 = 0; rp15 = 0;
312
313 for (i = 0; i < 64; i++)
314 {
315 cur = *bp++;
316 par ^= cur;
317 if (i & 0x01) rp5 ^= cur; else rp4 ^= cur;
318 if (i & 0x02) rp7 ^= cur; else rp6 ^= cur;
319 if (i & 0x04) rp9 ^= cur; else rp8 ^= cur;
320 if (i & 0x08) rp11 ^= cur; else rp10 ^= cur;
321 if (i & 0x10) rp13 ^= cur; else rp12 ^= cur;
322 if (i & 0x20) rp15 ^= cur; else rp14 ^= cur;
323 }
324 /*
325 we need to adapt the code generation for the fact that rp vars are now
326 long; also the column parity calculation needs to be changed.
327 we'll bring rp4 to 15 back to single byte entities by shifting and
328 xoring
329 */
330 rp4 ^= (rp4 >> 16); rp4 ^= (rp4 >> 8); rp4 &= 0xff;
331 rp5 ^= (rp5 >> 16); rp5 ^= (rp5 >> 8); rp5 &= 0xff;
332 rp6 ^= (rp6 >> 16); rp6 ^= (rp6 >> 8); rp6 &= 0xff;
333 rp7 ^= (rp7 >> 16); rp7 ^= (rp7 >> 8); rp7 &= 0xff;
334 rp8 ^= (rp8 >> 16); rp8 ^= (rp8 >> 8); rp8 &= 0xff;
335 rp9 ^= (rp9 >> 16); rp9 ^= (rp9 >> 8); rp9 &= 0xff;
336 rp10 ^= (rp10 >> 16); rp10 ^= (rp10 >> 8); rp10 &= 0xff;
337 rp11 ^= (rp11 >> 16); rp11 ^= (rp11 >> 8); rp11 &= 0xff;
338 rp12 ^= (rp12 >> 16); rp12 ^= (rp12 >> 8); rp12 &= 0xff;
339 rp13 ^= (rp13 >> 16); rp13 ^= (rp13 >> 8); rp13 &= 0xff;
340 rp14 ^= (rp14 >> 16); rp14 ^= (rp14 >> 8); rp14 &= 0xff;
341 rp15 ^= (rp15 >> 16); rp15 ^= (rp15 >> 8); rp15 &= 0xff;
342 rp3 = (par >> 16); rp3 ^= (rp3 >> 8); rp3 &= 0xff;
343 rp2 = par & 0xffff; rp2 ^= (rp2 >> 8); rp2 &= 0xff;
344 par ^= (par >> 16);
345 rp1 = (par >> 8); rp1 &= 0xff;
346 rp0 = (par & 0xff);
347 par ^= (par >> 8); par &= 0xff;
348
349 code[0] =
350 (parity[rp7] << 7) |
351 (parity[rp6] << 6) |
352 (parity[rp5] << 5) |
353 (parity[rp4] << 4) |
354 (parity[rp3] << 3) |
355 (parity[rp2] << 2) |
356 (parity[rp1] << 1) |
357 (parity[rp0]);
358 code[1] =
359 (parity[rp15] << 7) |
360 (parity[rp14] << 6) |
361 (parity[rp13] << 5) |
362 (parity[rp12] << 4) |
363 (parity[rp11] << 3) |
364 (parity[rp10] << 2) |
365 (parity[rp9] << 1) |
366 (parity[rp8]);
367 code[2] =
368 (parity[par & 0xf0] << 7) |
369 (parity[par & 0x0f] << 6) |
370 (parity[par & 0xcc] << 5) |
371 (parity[par & 0x33] << 4) |
372 (parity[par & 0xaa] << 3) |
373 (parity[par & 0x55] << 2);
374 code[0] = ~code[0];
375 code[1] = ~code[1];
376 code[2] = ~code[2];
377}
378
379The parity array is not shown any more. Note also that for these
380examples I kinda deviated from my regular programming style by allowing
381multiple statements on a line, not using { } in then and else blocks
382with only a single statement and by using operators like ^=
383
384
385Analysis 2
386==========
387
388The code (of course) works, and hurray: we are a little bit faster than
389the linux driver code (about 15%). But wait, don't cheer too quickly.
390THere is more to be gained.
391If we look at e.g. rp14 and rp15 we see that we either xor our data with
392rp14 or with rp15. However we also have par which goes over all data.
393This means there is no need to calculate rp14 as it can be calculated from
394rp15 through rp14 = par ^ rp15;
395(or if desired we can avoid calculating rp15 and calculate it from
396rp14). That is why some places refer to inverse parity.
397Of course the same thing holds for rp4/5, rp6/7, rp8/9, rp10/11 and rp12/13.
398Effectively this means we can eliminate the else clause from the if
399statements. Also we can optimise the calculation in the end a little bit
400by going from long to byte first. Actually we can even avoid the table
401lookups
402
403Attempt 3
404=========
405
406Odd replaced:
407 if (i & 0x01) rp5 ^= cur; else rp4 ^= cur;
408 if (i & 0x02) rp7 ^= cur; else rp6 ^= cur;
409 if (i & 0x04) rp9 ^= cur; else rp8 ^= cur;
410 if (i & 0x08) rp11 ^= cur; else rp10 ^= cur;
411 if (i & 0x10) rp13 ^= cur; else rp12 ^= cur;
412 if (i & 0x20) rp15 ^= cur; else rp14 ^= cur;
413with
414 if (i & 0x01) rp5 ^= cur;
415 if (i & 0x02) rp7 ^= cur;
416 if (i & 0x04) rp9 ^= cur;
417 if (i & 0x08) rp11 ^= cur;
418 if (i & 0x10) rp13 ^= cur;
419 if (i & 0x20) rp15 ^= cur;
420
421 and outside the loop added:
422 rp4 = par ^ rp5;
423 rp6 = par ^ rp7;
424 rp8 = par ^ rp9;
425 rp10 = par ^ rp11;
426 rp12 = par ^ rp13;
427 rp14 = par ^ rp15;
428
429And after that the code takes about 30% more time, although the number of
430statements is reduced. This is also reflected in the assembly code.
431
432
433Analysis 3
434==========
435
436Very weird. Guess it has to do with caching or instruction parallellism
437or so. I also tried on an eeePC (Celeron, clocked at 900 Mhz). Interesting
438observation was that this one is only 30% slower (according to time)
439executing the code as my 3Ghz D920 processor.
440
441Well, it was expected not to be easy so maybe instead move to a
442different track: let's move back to the code from attempt2 and do some
443loop unrolling. This will eliminate a few if statements. I'll try
444different amounts of unrolling to see what works best.
445
446
447Attempt 4
448=========
449
450Unrolled the loop 1, 2, 3 and 4 times.
451For 4 the code starts with:
452
453 for (i = 0; i < 4; i++)
454 {
455 cur = *bp++;
456 par ^= cur;
457 rp4 ^= cur;
458 rp6 ^= cur;
459 rp8 ^= cur;
460 rp10 ^= cur;
461 if (i & 0x1) rp13 ^= cur; else rp12 ^= cur;
462 if (i & 0x2) rp15 ^= cur; else rp14 ^= cur;
463 cur = *bp++;
464 par ^= cur;
465 rp5 ^= cur;
466 rp6 ^= cur;
467 ...
468
469
470Analysis 4
471==========
472
473Unrolling once gains about 15%
474Unrolling twice keeps the gain at about 15%
475Unrolling three times gives a gain of 30% compared to attempt 2.
476Unrolling four times gives a marginal improvement compared to unrolling
477three times.
478
479I decided to proceed with a four time unrolled loop anyway. It was my gut
480feeling that in the next steps I would obtain additional gain from it.
481
482The next step was triggered by the fact that par contains the xor of all
483bytes and rp4 and rp5 each contain the xor of half of the bytes.
484So in effect par = rp4 ^ rp5. But as xor is commutative we can also say
485that rp5 = par ^ rp4. So no need to keep both rp4 and rp5 around. We can
486eliminate rp5 (or rp4, but I already foresaw another optimisation).
487The same holds for rp6/7, rp8/9, rp10/11 rp12/13 and rp14/15.
488
489
490Attempt 5
491=========
492
493Effectively so all odd digit rp assignments in the loop were removed.
494This included the else clause of the if statements.
495Of course after the loop we need to correct things by adding code like:
496 rp5 = par ^ rp4;
497Also the initial assignments (rp5 = 0; etc) could be removed.
498Along the line I also removed the initialisation of rp0/1/2/3.
499
500
501Analysis 5
502==========
503
504Measurements showed this was a good move. The run-time roughly halved
505compared with attempt 4 with 4 times unrolled, and we only require 1/3rd
506of the processor time compared to the current code in the linux kernel.
507
508However, still I thought there was more. I didn't like all the if
509statements. Why not keep a running parity and only keep the last if
510statement. Time for yet another version!
511
512
513Attempt 6
514=========
515
516THe code within the for loop was changed to:
517
518 for (i = 0; i < 4; i++)
519 {
520 cur = *bp++; tmppar = cur; rp4 ^= cur;
521 cur = *bp++; tmppar ^= cur; rp6 ^= tmppar;
522 cur = *bp++; tmppar ^= cur; rp4 ^= cur;
523 cur = *bp++; tmppar ^= cur; rp8 ^= tmppar;
524
525 cur = *bp++; tmppar ^= cur; rp4 ^= cur; rp6 ^= cur;
526 cur = *bp++; tmppar ^= cur; rp6 ^= cur;
527 cur = *bp++; tmppar ^= cur; rp4 ^= cur;
528 cur = *bp++; tmppar ^= cur; rp10 ^= tmppar;
529
530 cur = *bp++; tmppar ^= cur; rp4 ^= cur; rp6 ^= cur; rp8 ^= cur;
531 cur = *bp++; tmppar ^= cur; rp6 ^= cur; rp8 ^= cur;
532 cur = *bp++; tmppar ^= cur; rp4 ^= cur; rp8 ^= cur;
533 cur = *bp++; tmppar ^= cur; rp8 ^= cur;
534
535 cur = *bp++; tmppar ^= cur; rp4 ^= cur; rp6 ^= cur;
536 cur = *bp++; tmppar ^= cur; rp6 ^= cur;
537 cur = *bp++; tmppar ^= cur; rp4 ^= cur;
538 cur = *bp++; tmppar ^= cur;
539
540 par ^= tmppar;
541 if ((i & 0x1) == 0) rp12 ^= tmppar;
542 if ((i & 0x2) == 0) rp14 ^= tmppar;
543 }
544
545As you can see tmppar is used to accumulate the parity within a for
546iteration. In the last 3 statements is is added to par and, if needed,
547to rp12 and rp14.
548
549While making the changes I also found that I could exploit that tmppar
550contains the running parity for this iteration. So instead of having:
551rp4 ^= cur; rp6 = cur;
552I removed the rp6 = cur; statement and did rp6 ^= tmppar; on next
553statement. A similar change was done for rp8 and rp10
554
555
556Analysis 6
557==========
558
559Measuring this code again showed big gain. When executing the original
560linux code 1 million times, this took about 1 second on my system.
561(using time to measure the performance). After this iteration I was back
562to 0.075 sec. Actually I had to decide to start measuring over 10
563million interations in order not to loose too much accuracy. This one
564definitely seemed to be the jackpot!
565
566There is a little bit more room for improvement though. There are three
567places with statements:
568rp4 ^= cur; rp6 ^= cur;
569It seems more efficient to also maintain a variable rp4_6 in the while
570loop; This eliminates 3 statements per loop. Of course after the loop we
571need to correct by adding:
572 rp4 ^= rp4_6;
573 rp6 ^= rp4_6
574Furthermore there are 4 sequential assingments to rp8. This can be
575encoded slightly more efficient by saving tmppar before those 4 lines
576and later do rp8 = rp8 ^ tmppar ^ notrp8;
577(where notrp8 is the value of rp8 before those 4 lines).
578Again a use of the commutative property of xor.
579Time for a new test!
580
581
582Attempt 7
583=========
584
585The new code now looks like:
586
587 for (i = 0; i < 4; i++)
588 {
589 cur = *bp++; tmppar = cur; rp4 ^= cur;
590 cur = *bp++; tmppar ^= cur; rp6 ^= tmppar;
591 cur = *bp++; tmppar ^= cur; rp4 ^= cur;
592 cur = *bp++; tmppar ^= cur; rp8 ^= tmppar;
593
594 cur = *bp++; tmppar ^= cur; rp4_6 ^= cur;
595 cur = *bp++; tmppar ^= cur; rp6 ^= cur;
596 cur = *bp++; tmppar ^= cur; rp4 ^= cur;
597 cur = *bp++; tmppar ^= cur; rp10 ^= tmppar;
598
599 notrp8 = tmppar;
600 cur = *bp++; tmppar ^= cur; rp4_6 ^= cur;
601 cur = *bp++; tmppar ^= cur; rp6 ^= cur;
602 cur = *bp++; tmppar ^= cur; rp4 ^= cur;
603 cur = *bp++; tmppar ^= cur;
604 rp8 = rp8 ^ tmppar ^ notrp8;
605
606 cur = *bp++; tmppar ^= cur; rp4_6 ^= cur;
607 cur = *bp++; tmppar ^= cur; rp6 ^= cur;
608 cur = *bp++; tmppar ^= cur; rp4 ^= cur;
609 cur = *bp++; tmppar ^= cur;
610
611 par ^= tmppar;
612 if ((i & 0x1) == 0) rp12 ^= tmppar;
613 if ((i & 0x2) == 0) rp14 ^= tmppar;
614 }
615 rp4 ^= rp4_6;
616 rp6 ^= rp4_6;
617
618
619Not a big change, but every penny counts :-)
620
621
622Analysis 7
623==========
624
625Acutally this made things worse. Not very much, but I don't want to move
626into the wrong direction. Maybe something to investigate later. Could
627have to do with caching again.
628
629Guess that is what there is to win within the loop. Maybe unrolling one
630more time will help. I'll keep the optimisations from 7 for now.
631
632
633Attempt 8
634=========
635
636Unrolled the loop one more time.
637
638
639Analysis 8
640==========
641
642This makes things worse. Let's stick with attempt 6 and continue from there.
643Although it seems that the code within the loop cannot be optimised
644further there is still room to optimize the generation of the ecc codes.
645We can simply calcualate the total parity. If this is 0 then rp4 = rp5
646etc. If the parity is 1, then rp4 = !rp5;
647But if rp4 = rp5 we do not need rp5 etc. We can just write the even bits
648in the result byte and then do something like
649 code[0] |= (code[0] << 1);
650Lets test this.
651
652
653Attempt 9
654=========
655
656Changed the code but again this slightly degrades performance. Tried all
657kind of other things, like having dedicated parity arrays to avoid the
658shift after parity[rp7] << 7; No gain.
659Change the lookup using the parity array by using shift operators (e.g.
660replace parity[rp7] << 7 with:
661rp7 ^= (rp7 << 4);
662rp7 ^= (rp7 << 2);
663rp7 ^= (rp7 << 1);
664rp7 &= 0x80;
665No gain.
666
667The only marginal change was inverting the parity bits, so we can remove
668the last three invert statements.
669
670Ah well, pity this does not deliver more. Then again 10 million
671iterations using the linux driver code takes between 13 and 13.5
672seconds, whereas my code now takes about 0.73 seconds for those 10
673million iterations. So basically I've improved the performance by a
674factor 18 on my system. Not that bad. Of course on different hardware
675you will get different results. No warranties!
676
677But of course there is no such thing as a free lunch. The codesize almost
678tripled (from 562 bytes to 1434 bytes). Then again, it is not that much.
679
680
681Correcting errors
682=================
683
684For correcting errors I again used the ST application note as a starter,
685but I also peeked at the existing code.
686The algorithm itself is pretty straightforward. Just xor the given and
687the calculated ecc. If all bytes are 0 there is no problem. If 11 bits
688are 1 we have one correctable bit error. If there is 1 bit 1, we have an
689error in the given ecc code.
690It proved to be fastest to do some table lookups. Performance gain
691introduced by this is about a factor 2 on my system when a repair had to
692be done, and 1% or so if no repair had to be done.
693Code size increased from 330 bytes to 686 bytes for this function.
694(gcc 4.2, -O3)
695
696
697Conclusion
698==========
699
700The gain when calculating the ecc is tremendous. Om my development hardware
701a speedup of a factor of 18 for ecc calculation was achieved. On a test on an
702embedded system with a MIPS core a factor 7 was obtained.
703On a test with a Linksys NSLU2 (ARMv5TE processor) the speedup was a factor
7045 (big endian mode, gcc 4.1.2, -O3)
705For correction not much gain could be obtained (as bitflips are rare). Then
706again there are also much less cycles spent there.
707
708It seems there is not much more gain possible in this, at least when
709programmed in C. Of course it might be possible to squeeze something more
710out of it with an assembler program, but due to pipeline behaviour etc
711this is very tricky (at least for intel hw).
712
713Author: Frans Meulenbroeks
714Copyright (C) 2008 Koninklijke Philips Electronics NV.
diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt
index 5ce0952aa065..10a0263ebb3f 100644
--- a/Documentation/sysrq.txt
+++ b/Documentation/sysrq.txt
@@ -95,7 +95,9 @@ On all - write a character to /proc/sysrq-trigger. e.g.:
95 95
96'p' - Will dump the current registers and flags to your console. 96'p' - Will dump the current registers and flags to your console.
97 97
98'q' - Will dump a list of all running timers. 98'q' - Will dump per CPU lists of all armed hrtimers (but NOT regular
99 timer_list timers) and detailed information about all
100 clockevent devices.
99 101
100'r' - Turns off keyboard raw mode and sets it to XLATE. 102'r' - Turns off keyboard raw mode and sets it to XLATE.
101 103
diff --git a/Documentation/tracepoints.txt b/Documentation/tracepoints.txt
new file mode 100644
index 000000000000..5d354e167494
--- /dev/null
+++ b/Documentation/tracepoints.txt
@@ -0,0 +1,101 @@
1 Using the Linux Kernel Tracepoints
2
3 Mathieu Desnoyers
4
5
6This document introduces Linux Kernel Tracepoints and their use. It provides
7examples of how to insert tracepoints in the kernel and connect probe functions
8to them and provides some examples of probe functions.
9
10
11* Purpose of tracepoints
12
13A tracepoint placed in code provides a hook to call a function (probe) that you
14can provide at runtime. A tracepoint can be "on" (a probe is connected to it) or
15"off" (no probe is attached). When a tracepoint is "off" it has no effect,
16except for adding a tiny time penalty (checking a condition for a branch) and
17space penalty (adding a few bytes for the function call at the end of the
18instrumented function and adds a data structure in a separate section). When a
19tracepoint is "on", the function you provide is called each time the tracepoint
20is executed, in the execution context of the caller. When the function provided
21ends its execution, it returns to the caller (continuing from the tracepoint
22site).
23
24You can put tracepoints at important locations in the code. They are
25lightweight hooks that can pass an arbitrary number of parameters,
26which prototypes are described in a tracepoint declaration placed in a header
27file.
28
29They can be used for tracing and performance accounting.
30
31
32* Usage
33
34Two elements are required for tracepoints :
35
36- A tracepoint definition, placed in a header file.
37- The tracepoint statement, in C code.
38
39In order to use tracepoints, you should include linux/tracepoint.h.
40
41In include/trace/subsys.h :
42
43#include <linux/tracepoint.h>
44
45DEFINE_TRACE(subsys_eventname,
46 TPPTOTO(int firstarg, struct task_struct *p),
47 TPARGS(firstarg, p));
48
49In subsys/file.c (where the tracing statement must be added) :
50
51#include <trace/subsys.h>
52
53void somefct(void)
54{
55 ...
56 trace_subsys_eventname(arg, task);
57 ...
58}
59
60Where :
61- subsys_eventname is an identifier unique to your event
62 - subsys is the name of your subsystem.
63 - eventname is the name of the event to trace.
64- TPPTOTO(int firstarg, struct task_struct *p) is the prototype of the function
65 called by this tracepoint.
66- TPARGS(firstarg, p) are the parameters names, same as found in the prototype.
67
68Connecting a function (probe) to a tracepoint is done by providing a probe
69(function to call) for the specific tracepoint through
70register_trace_subsys_eventname(). Removing a probe is done through
71unregister_trace_subsys_eventname(); it will remove the probe sure there is no
72caller left using the probe when it returns. Probe removal is preempt-safe
73because preemption is disabled around the probe call. See the "Probe example"
74section below for a sample probe module.
75
76The tracepoint mechanism supports inserting multiple instances of the same
77tracepoint, but a single definition must be made of a given tracepoint name over
78all the kernel to make sure no type conflict will occur. Name mangling of the
79tracepoints is done using the prototypes to make sure typing is correct.
80Verification of probe type correctness is done at the registration site by the
81compiler. Tracepoints can be put in inline functions, inlined static functions,
82and unrolled loops as well as regular functions.
83
84The naming scheme "subsys_event" is suggested here as a convention intended
85to limit collisions. Tracepoint names are global to the kernel: they are
86considered as being the same whether they are in the core kernel image or in
87modules.
88
89
90* Probe / tracepoint example
91
92See the example provided in samples/tracepoints/src
93
94Compile them with your kernel.
95
96Run, as root :
97modprobe tracepoint-example (insmod order is not important)
98modprobe tracepoint-probe-example
99cat /proc/tracepoint-example (returns an expected error)
100rmmod tracepoint-example tracepoint-probe-example
101dmesg
diff --git a/Documentation/tracers/mmiotrace.txt b/Documentation/tracers/mmiotrace.txt
index a4afb560a45b..5bbbe2096223 100644
--- a/Documentation/tracers/mmiotrace.txt
+++ b/Documentation/tracers/mmiotrace.txt
@@ -36,7 +36,7 @@ $ mount -t debugfs debugfs /debug
36$ echo mmiotrace > /debug/tracing/current_tracer 36$ echo mmiotrace > /debug/tracing/current_tracer
37$ cat /debug/tracing/trace_pipe > mydump.txt & 37$ cat /debug/tracing/trace_pipe > mydump.txt &
38Start X or whatever. 38Start X or whatever.
39$ echo "X is up" > /debug/tracing/marker 39$ echo "X is up" > /debug/tracing/trace_marker
40$ echo none > /debug/tracing/current_tracer 40$ echo none > /debug/tracing/current_tracer
41Check for lost events. 41Check for lost events.
42 42
@@ -59,9 +59,8 @@ The 'cat' process should stay running (sleeping) in the background.
59Load the driver you want to trace and use it. Mmiotrace will only catch MMIO 59Load the driver you want to trace and use it. Mmiotrace will only catch MMIO
60accesses to areas that are ioremapped while mmiotrace is active. 60accesses to areas that are ioremapped while mmiotrace is active.
61 61
62[Unimplemented feature:]
63During tracing you can place comments (markers) into the trace by 62During tracing you can place comments (markers) into the trace by
64$ echo "X is up" > /debug/tracing/marker 63$ echo "X is up" > /debug/tracing/trace_marker
65This makes it easier to see which part of the (huge) trace corresponds to 64This makes it easier to see which part of the (huge) trace corresponds to
66which action. It is recommended to place descriptive markers about what you 65which action. It is recommended to place descriptive markers about what you
67do. 66do.
diff --git a/Documentation/usb/anchors.txt b/Documentation/usb/anchors.txt
index 5e6b64c20d25..6f24f566955a 100644
--- a/Documentation/usb/anchors.txt
+++ b/Documentation/usb/anchors.txt
@@ -52,6 +52,11 @@ Therefore no guarantee is made that the URBs have been unlinked when
52the call returns. They may be unlinked later but will be unlinked in 52the call returns. They may be unlinked later but will be unlinked in
53finite time. 53finite time.
54 54
55usb_scuttle_anchored_urbs()
56---------------------------
57
58All URBs of an anchor are unanchored en masse.
59
55usb_wait_anchor_empty_timeout() 60usb_wait_anchor_empty_timeout()
56------------------------------- 61-------------------------------
57 62
@@ -59,4 +64,16 @@ This function waits for all URBs associated with an anchor to finish
59or a timeout, whichever comes first. Its return value will tell you 64or a timeout, whichever comes first. Its return value will tell you
60whether the timeout was reached. 65whether the timeout was reached.
61 66
67usb_anchor_empty()
68------------------
69
70Returns true if no URBs are associated with an anchor. Locking
71is the caller's responsibility.
72
73usb_get_from_anchor()
74---------------------
62 75
76Returns the oldest anchored URB of an anchor. The URB is unanchored
77and returned with a reference. As you may mix URBs to several
78destinations in one anchor you have no guarantee the chronologically
79first submitted URB is returned. \ No newline at end of file
diff --git a/Documentation/usb/misc_usbsevseg.txt b/Documentation/usb/misc_usbsevseg.txt
new file mode 100644
index 000000000000..0f6be4f9930b
--- /dev/null
+++ b/Documentation/usb/misc_usbsevseg.txt
@@ -0,0 +1,46 @@
1USB 7-Segment Numeric Display
2Manufactured by Delcom Engineering
3
4Device Information
5------------------
6USB VENDOR_ID 0x0fc5
7USB PRODUCT_ID 0x1227
8Both the 6 character and 8 character displays have PRODUCT_ID,
9and according to Delcom Engineering no queryable information
10can be obtained from the device to tell them apart.
11
12Device Modes
13------------
14By default, the driver assumes the display is only 6 characters
15The mode for 6 characters is:
16 MSB 0x06; LSB 0x3f
17For the 8 character display:
18 MSB 0x08; LSB 0xff
19The device can accept "text" either in raw, hex, or ascii textmode.
20raw controls each segment manually,
21hex expects a value between 0-15 per character,
22ascii expects a value between '0'-'9' and 'A'-'F'.
23The default is ascii.
24
25Device Operation
26----------------
271. Turn on the device:
28 echo 1 > /sys/bus/usb/.../powered
292. Set the device's mode:
30 echo $mode_msb > /sys/bus/usb/.../mode_msb
31 echo $mode_lsb > /sys/bus/usb/.../mode_lsb
323. Set the textmode:
33 echo $textmode > /sys/bus/usb/.../textmode
344. set the text (for example):
35 echo "123ABC" > /sys/bus/usb/.../text (ascii)
36 echo "A1B2" > /sys/bus/usb/.../text (ascii)
37 echo -ne "\x01\x02\x03" > /sys/bus/usb/.../text (hex)
385. Set the decimal places.
39 The device has either 6 or 8 decimal points.
40 to set the nth decimal place calculate 10 ** n
41 and echo it in to /sys/bus/usb/.../decimals
42 To set multiple decimals points sum up each power.
43 For example, to set the 0th and 3rd decimal place
44 echo 1001 > /sys/bus/usb/.../decimals
45
46
diff --git a/Documentation/usb/power-management.txt b/Documentation/usb/power-management.txt
index 9d31140e3f5b..e48ea1d51010 100644
--- a/Documentation/usb/power-management.txt
+++ b/Documentation/usb/power-management.txt
@@ -350,12 +350,12 @@ without holding the mutex.
350 350
351There also are a couple of utility routines drivers can use: 351There also are a couple of utility routines drivers can use:
352 352
353 usb_autopm_enable() sets pm_usage_cnt to 1 and then calls 353 usb_autopm_enable() sets pm_usage_cnt to 0 and then calls
354 usb_autopm_set_interface(), which will attempt an autoresume.
355
356 usb_autopm_disable() sets pm_usage_cnt to 0 and then calls
357 usb_autopm_set_interface(), which will attempt an autosuspend. 354 usb_autopm_set_interface(), which will attempt an autosuspend.
358 355
356 usb_autopm_disable() sets pm_usage_cnt to 1 and then calls
357 usb_autopm_set_interface(), which will attempt an autoresume.
358
359The conventional usage pattern is that a driver calls 359The conventional usage pattern is that a driver calls
360usb_autopm_get_interface() in its open routine and 360usb_autopm_get_interface() in its open routine and
361usb_autopm_put_interface() in its close or release routine. But 361usb_autopm_put_interface() in its close or release routine. But
diff --git a/Documentation/video4linux/CARDLIST.au0828 b/Documentation/video4linux/CARDLIST.au0828
index aa05e5bb22fb..d5cb4ea287b2 100644
--- a/Documentation/video4linux/CARDLIST.au0828
+++ b/Documentation/video4linux/CARDLIST.au0828
@@ -1,5 +1,5 @@
1 0 -> Unknown board (au0828) 1 0 -> Unknown board (au0828)
2 1 -> Hauppauge HVR950Q (au0828) [2040:7200,2040:7210,2040:7217,2040:721b,2040:721f,2040:7280,0fd9:0008] 2 1 -> Hauppauge HVR950Q (au0828) [2040:7200,2040:7210,2040:7217,2040:721b,2040:721e,2040:721f,2040:7280,0fd9:0008]
3 2 -> Hauppauge HVR850 (au0828) [2040:7240] 3 2 -> Hauppauge HVR850 (au0828) [2040:7240]
4 3 -> DViCO FusionHDTV USB (au0828) [0fe9:d620] 4 3 -> DViCO FusionHDTV USB (au0828) [0fe9:d620]
5 4 -> Hauppauge HVR950Q rev xxF8 (au0828) [2040:7201,2040:7211,2040:7281] 5 4 -> Hauppauge HVR950Q rev xxF8 (au0828) [2040:7201,2040:7211,2040:7281]
diff --git a/Documentation/video4linux/CARDLIST.tuner b/Documentation/video4linux/CARDLIST.tuner
index 30bbdda68d03..691d2f37dc57 100644
--- a/Documentation/video4linux/CARDLIST.tuner
+++ b/Documentation/video4linux/CARDLIST.tuner
@@ -75,3 +75,4 @@ tuner=73 - Samsung TCPG 6121P30A
75tuner=75 - Philips TEA5761 FM Radio 75tuner=75 - Philips TEA5761 FM Radio
76tuner=76 - Xceive 5000 tuner 76tuner=76 - Xceive 5000 tuner
77tuner=77 - TCL tuner MF02GIP-5N-E 77tuner=77 - TCL tuner MF02GIP-5N-E
78tuner=78 - Philips FMD1216MEX MK3 Hybrid Tuner
diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt
new file mode 100644
index 000000000000..125eed560e5a
--- /dev/null
+++ b/Documentation/vm/unevictable-lru.txt
@@ -0,0 +1,615 @@
1
2This document describes the Linux memory management "Unevictable LRU"
3infrastructure and the use of this infrastructure to manage several types
4of "unevictable" pages. The document attempts to provide the overall
5rationale behind this mechanism and the rationale for some of the design
6decisions that drove the implementation. The latter design rationale is
7discussed in the context of an implementation description. Admittedly, one
8can obtain the implementation details--the "what does it do?"--by reading the
9code. One hopes that the descriptions below add value by provide the answer
10to "why does it do that?".
11
12Unevictable LRU Infrastructure:
13
14The Unevictable LRU adds an additional LRU list to track unevictable pages
15and to hide these pages from vmscan. This mechanism is based on a patch by
16Larry Woodman of Red Hat to address several scalability problems with page
17reclaim in Linux. The problems have been observed at customer sites on large
18memory x86_64 systems. For example, a non-numal x86_64 platform with 128GB
19of main memory will have over 32 million 4k pages in a single zone. When a
20large fraction of these pages are not evictable for any reason [see below],
21vmscan will spend a lot of time scanning the LRU lists looking for the small
22fraction of pages that are evictable. This can result in a situation where
23all cpus are spending 100% of their time in vmscan for hours or days on end,
24with the system completely unresponsive.
25
26The Unevictable LRU infrastructure addresses the following classes of
27unevictable pages:
28
29+ page owned by ramfs
30+ page mapped into SHM_LOCKed shared memory regions
31+ page mapped into VM_LOCKED [mlock()ed] vmas
32
33The infrastructure might be able to handle other conditions that make pages
34unevictable, either by definition or by circumstance, in the future.
35
36
37The Unevictable LRU List
38
39The Unevictable LRU infrastructure consists of an additional, per-zone, LRU list
40called the "unevictable" list and an associated page flag, PG_unevictable, to
41indicate that the page is being managed on the unevictable list. The
42PG_unevictable flag is analogous to, and mutually exclusive with, the PG_active
43flag in that it indicates on which LRU list a page resides when PG_lru is set.
44The unevictable LRU list is source configurable based on the UNEVICTABLE_LRU
45Kconfig option.
46
47The Unevictable LRU infrastructure maintains unevictable pages on an additional
48LRU list for a few reasons:
49
501) We get to "treat unevictable pages just like we treat other pages in the
51 system, which means we get to use the same code to manipulate them, the
52 same code to isolate them (for migrate, etc.), the same code to keep track
53 of the statistics, etc..." [Rik van Riel]
54
552) We want to be able to migrate unevictable pages between nodes--for memory
56 defragmentation, workload management and memory hotplug. The linux kernel
57 can only migrate pages that it can successfully isolate from the lru lists.
58 If we were to maintain pages elsewise than on an lru-like list, where they
59 can be found by isolate_lru_page(), we would prevent their migration, unless
60 we reworked migration code to find the unevictable pages.
61
62
63The unevictable LRU list does not differentiate between file backed and swap
64backed [anon] pages. This differentiation is only important while the pages
65are, in fact, evictable.
66
67The unevictable LRU list benefits from the "arrayification" of the per-zone
68LRU lists and statistics originally proposed and posted by Christoph Lameter.
69
70The unevictable list does not use the lru pagevec mechanism. Rather,
71unevictable pages are placed directly on the page's zone's unevictable
72list under the zone lru_lock. The reason for this is to prevent stranding
73of pages on the unevictable list when one task has the page isolated from the
74lru and other tasks are changing the "evictability" state of the page.
75
76
77Unevictable LRU and Memory Controller Interaction
78
79The memory controller data structure automatically gets a per zone unevictable
80lru list as a result of the "arrayification" of the per-zone LRU lists. The
81memory controller tracks the movement of pages to and from the unevictable list.
82When a memory control group comes under memory pressure, the controller will
83not attempt to reclaim pages on the unevictable list. This has a couple of
84effects. Because the pages are "hidden" from reclaim on the unevictable list,
85the reclaim process can be more efficient, dealing only with pages that have
86a chance of being reclaimed. On the other hand, if too many of the pages
87charged to the control group are unevictable, the evictable portion of the
88working set of the tasks in the control group may not fit into the available
89memory. This can cause the control group to thrash or to oom-kill tasks.
90
91
92Unevictable LRU: Detecting Unevictable Pages
93
94The function page_evictable(page, vma) in vmscan.c determines whether a
95page is evictable or not. For ramfs pages and pages in SHM_LOCKed regions,
96page_evictable() tests a new address space flag, AS_UNEVICTABLE, in the page's
97address space using a wrapper function. Wrapper functions are used to set,
98clear and test the flag to reduce the requirement for #ifdef's throughout the
99source code. AS_UNEVICTABLE is set on ramfs inode/mapping when it is created.
100This flag remains for the life of the inode.
101
102For shared memory regions, AS_UNEVICTABLE is set when an application
103successfully SHM_LOCKs the region and is removed when the region is
104SHM_UNLOCKed. Note that shmctl(SHM_LOCK, ...) does not populate the page
105tables for the region as does, for example, mlock(). So, we make no special
106effort to push any pages in the SHM_LOCKed region to the unevictable list.
107Vmscan will do this when/if it encounters the pages during reclaim. On
108SHM_UNLOCK, shmctl() scans the pages in the region and "rescues" them from the
109unevictable list if no other condition keeps them unevictable. If a SHM_LOCKed
110region is destroyed, the pages are also "rescued" from the unevictable list in
111the process of freeing them.
112
113page_evictable() detects mlock()ed pages by testing an additional page flag,
114PG_mlocked via the PageMlocked() wrapper. If the page is NOT mlocked, and a
115non-NULL vma is supplied, page_evictable() will check whether the vma is
116VM_LOCKED via is_mlocked_vma(). is_mlocked_vma() will SetPageMlocked() and
117update the appropriate statistics if the vma is VM_LOCKED. This method allows
118efficient "culling" of pages in the fault path that are being faulted in to
119VM_LOCKED vmas.
120
121
122Unevictable Pages and Vmscan [shrink_*_list()]
123
124If unevictable pages are culled in the fault path, or moved to the unevictable
125list at mlock() or mmap() time, vmscan will never encounter the pages until
126they have become evictable again, for example, via munlock() and have been
127"rescued" from the unevictable list. However, there may be situations where we
128decide, for the sake of expediency, to leave a unevictable page on one of the
129regular active/inactive LRU lists for vmscan to deal with. Vmscan checks for
130such pages in all of the shrink_{active|inactive|page}_list() functions and
131will "cull" such pages that it encounters--that is, it diverts those pages to
132the unevictable list for the zone being scanned.
133
134There may be situations where a page is mapped into a VM_LOCKED vma, but the
135page is not marked as PageMlocked. Such pages will make it all the way to
136shrink_page_list() where they will be detected when vmscan walks the reverse
137map in try_to_unmap(). If try_to_unmap() returns SWAP_MLOCK, shrink_page_list()
138will cull the page at that point.
139
140Note that for anonymous pages, shrink_page_list() attempts to add the page to
141the swap cache before it tries to unmap the page. To avoid this unnecessary
142consumption of swap space, shrink_page_list() calls try_to_munlock() to check
143whether any VM_LOCKED vmas map the page without attempting to unmap the page.
144If try_to_munlock() returns SWAP_MLOCK, shrink_page_list() will cull the page
145without consuming swap space. try_to_munlock() will be described below.
146
147To "cull" an unevictable page, vmscan simply puts the page back on the lru
148list using putback_lru_page()--the inverse operation to isolate_lru_page()--
149after dropping the page lock. Because the condition which makes the page
150unevictable may change once the page is unlocked, putback_lru_page() will
151recheck the unevictable state of a page that it places on the unevictable lru
152list. If the page has become unevictable, putback_lru_page() removes it from
153the list and retries, including the page_unevictable() test. Because such a
154race is a rare event and movement of pages onto the unevictable list should be
155rare, these extra evictabilty checks should not occur in the majority of calls
156to putback_lru_page().
157
158
159Mlocked Page: Prior Work
160
161The "Unevictable Mlocked Pages" infrastructure is based on work originally
162posted by Nick Piggin in an RFC patch entitled "mm: mlocked pages off LRU".
163Nick posted his patch as an alternative to a patch posted by Christoph
164Lameter to achieve the same objective--hiding mlocked pages from vmscan.
165In Nick's patch, he used one of the struct page lru list link fields as a count
166of VM_LOCKED vmas that map the page. This use of the link field for a count
167prevented the management of the pages on an LRU list. Thus, mlocked pages were
168not migratable as isolate_lru_page() could not find them and the lru list link
169field was not available to the migration subsystem. Nick resolved this by
170putting mlocked pages back on the lru list before attempting to isolate them,
171thus abandoning the count of VM_LOCKED vmas. When Nick's patch was integrated
172with the Unevictable LRU work, the count was replaced by walking the reverse
173map to determine whether any VM_LOCKED vmas mapped the page. More on this
174below.
175
176
177Mlocked Pages: Basic Management
178
179Mlocked pages--pages mapped into a VM_LOCKED vma--represent one class of
180unevictable pages. When such a page has been "noticed" by the memory
181management subsystem, the page is marked with the PG_mlocked [PageMlocked()]
182flag. A PageMlocked() page will be placed on the unevictable LRU list when
183it is added to the LRU. Pages can be "noticed" by memory management in
184several places:
185
1861) in the mlock()/mlockall() system call handlers.
1872) in the mmap() system call handler when mmap()ing a region with the
188 MAP_LOCKED flag, or mmap()ing a region in a task that has called
189 mlockall() with the MCL_FUTURE flag. Both of these conditions result
190 in the VM_LOCKED flag being set for the vma.
1913) in the fault path, if mlocked pages are "culled" in the fault path,
192 and when a VM_LOCKED stack segment is expanded.
1934) as mentioned above, in vmscan:shrink_page_list() with attempting to
194 reclaim a page in a VM_LOCKED vma--via try_to_unmap() or try_to_munlock().
195
196Mlocked pages become unlocked and rescued from the unevictable list when:
197
1981) mapped in a range unlocked via the munlock()/munlockall() system calls.
1992) munmapped() out of the last VM_LOCKED vma that maps the page, including
200 unmapping at task exit.
2013) when the page is truncated from the last VM_LOCKED vma of an mmap()ed file.
2024) before a page is COWed in a VM_LOCKED vma.
203
204
205Mlocked Pages: mlock()/mlockall() System Call Handling
206
207Both [do_]mlock() and [do_]mlockall() system call handlers call mlock_fixup()
208for each vma in the range specified by the call. In the case of mlockall(),
209this is the entire active address space of the task. Note that mlock_fixup()
210is used for both mlock()ing and munlock()ing a range of memory. A call to
211mlock() an already VM_LOCKED vma, or to munlock() a vma that is not VM_LOCKED
212is treated as a no-op--mlock_fixup() simply returns.
213
214If the vma passes some filtering described in "Mlocked Pages: Filtering Vmas"
215below, mlock_fixup() will attempt to merge the vma with its neighbors or split
216off a subset of the vma if the range does not cover the entire vma. Once the
217vma has been merged or split or neither, mlock_fixup() will call
218__mlock_vma_pages_range() to fault in the pages via get_user_pages() and
219to mark the pages as mlocked via mlock_vma_page().
220
221Note that the vma being mlocked might be mapped with PROT_NONE. In this case,
222get_user_pages() will be unable to fault in the pages. That's OK. If pages
223do end up getting faulted into this VM_LOCKED vma, we'll handle them in the
224fault path or in vmscan.
225
226Also note that a page returned by get_user_pages() could be truncated or
227migrated out from under us, while we're trying to mlock it. To detect
228this, __mlock_vma_pages_range() tests the page_mapping after acquiring
229the page lock. If the page is still associated with its mapping, we'll
230go ahead and call mlock_vma_page(). If the mapping is gone, we just
231unlock the page and move on. Worse case, this results in page mapped
232in a VM_LOCKED vma remaining on a normal LRU list without being
233PageMlocked(). Again, vmscan will detect and cull such pages.
234
235mlock_vma_page(), called with the page locked [N.B., not "mlocked"], will
236TestSetPageMlocked() for each page returned by get_user_pages(). We use
237TestSetPageMlocked() because the page might already be mlocked by another
238task/vma and we don't want to do extra work. We especially do not want to
239count an mlocked page more than once in the statistics. If the page was
240already mlocked, mlock_vma_page() is done.
241
242If the page was NOT already mlocked, mlock_vma_page() attempts to isolate the
243page from the LRU, as it is likely on the appropriate active or inactive list
244at that time. If the isolate_lru_page() succeeds, mlock_vma_page() will
245putback the page--putback_lru_page()--which will notice that the page is now
246mlocked and divert the page to the zone's unevictable LRU list. If
247mlock_vma_page() is unable to isolate the page from the LRU, vmscan will handle
248it later if/when it attempts to reclaim the page.
249
250
251Mlocked Pages: Filtering Special Vmas
252
253mlock_fixup() filters several classes of "special" vmas:
254
2551) vmas with VM_IO|VM_PFNMAP set are skipped entirely. The pages behind
256 these mappings are inherently pinned, so we don't need to mark them as
257 mlocked. In any case, most of the pages have no struct page in which to
258 so mark the page. Because of this, get_user_pages() will fail for these
259 vmas, so there is no sense in attempting to visit them.
260
2612) vmas mapping hugetlbfs page are already effectively pinned into memory.
262 We don't need nor want to mlock() these pages. However, to preserve the
263 prior behavior of mlock()--before the unevictable/mlock changes--mlock_fixup()
264 will call make_pages_present() in the hugetlbfs vma range to allocate the
265 huge pages and populate the ptes.
266
2673) vmas with VM_DONTEXPAND|VM_RESERVED are generally user space mappings of
268 kernel pages, such as the vdso page, relay channel pages, etc. These pages
269 are inherently unevictable and are not managed on the LRU lists.
270 mlock_fixup() treats these vmas the same as hugetlbfs vmas. It calls
271 make_pages_present() to populate the ptes.
272
273Note that for all of these special vmas, mlock_fixup() does not set the
274VM_LOCKED flag. Therefore, we won't have to deal with them later during
275munlock() or munmap()--for example, at task exit. Neither does mlock_fixup()
276account these vmas against the task's "locked_vm".
277
278Mlocked Pages: Downgrading the Mmap Semaphore.
279
280mlock_fixup() must be called with the mmap semaphore held for write, because
281it may have to merge or split vmas. However, mlocking a large region of
282memory can take a long time--especially if vmscan must reclaim pages to
283satisfy the regions requirements. Faulting in a large region with the mmap
284semaphore held for write can hold off other faults on the address space, in
285the case of a multi-threaded task. It can also hold off scans of the task's
286address space via /proc. While testing under heavy load, it was observed that
287the ps(1) command could be held off for many minutes while a large segment was
288mlock()ed down.
289
290To address this issue, and to make the system more responsive during mlock()ing
291of large segments, mlock_fixup() downgrades the mmap semaphore to read mode
292during the call to __mlock_vma_pages_range(). This works fine. However, the
293callers of mlock_fixup() expect the semaphore to be returned in write mode.
294So, mlock_fixup() "upgrades" the semphore to write mode. Linux does not
295support an atomic upgrade_sem() call, so mlock_fixup() must drop the semaphore
296and reacquire it in write mode. In a multi-threaded task, it is possible for
297the task memory map to change while the semaphore is dropped. Therefore,
298mlock_fixup() looks up the vma at the range start address after reacquiring
299the semaphore in write mode and verifies that it still covers the original
300range. If not, mlock_fixup() returns an error [-EAGAIN]. All callers of
301mlock_fixup() have been changed to deal with this new error condition.
302
303Note: when munlocking a region, all of the pages should already be resident--
304unless we have racing threads mlocking() and munlocking() regions. So,
305unlocking should not have to wait for page allocations nor faults of any kind.
306Therefore mlock_fixup() does not downgrade the semaphore for munlock().
307
308
309Mlocked Pages: munlock()/munlockall() System Call Handling
310
311The munlock() and munlockall() system calls are handled by the same functions--
312do_mlock[all]()--as the mlock() and mlockall() system calls with the unlock
313vs lock operation indicated by an argument. So, these system calls are also
314handled by mlock_fixup(). Again, if called for an already munlock()ed vma,
315mlock_fixup() simply returns. Because of the vma filtering discussed above,
316VM_LOCKED will not be set in any "special" vmas. So, these vmas will be
317ignored for munlock.
318
319If the vma is VM_LOCKED, mlock_fixup() again attempts to merge or split off
320the specified range. The range is then munlocked via the function
321__mlock_vma_pages_range()--the same function used to mlock a vma range--
322passing a flag to indicate that munlock() is being performed.
323
324Because the vma access protections could have been changed to PROT_NONE after
325faulting in and mlocking some pages, get_user_pages() was unreliable for visiting
326these pages for munlocking. Because we don't want to leave pages mlocked(),
327get_user_pages() was enhanced to accept a flag to ignore the permissions when
328fetching the pages--all of which should be resident as a result of previous
329mlock()ing.
330
331For munlock(), __mlock_vma_pages_range() unlocks individual pages by calling
332munlock_vma_page(). munlock_vma_page() unconditionally clears the PG_mlocked
333flag using TestClearPageMlocked(). As with mlock_vma_page(), munlock_vma_page()
334use the Test*PageMlocked() function to handle the case where the page might
335have already been unlocked by another task. If the page was mlocked,
336munlock_vma_page() updates that zone statistics for the number of mlocked
337pages. Note, however, that at this point we haven't checked whether the page
338is mapped by other VM_LOCKED vmas.
339
340We can't call try_to_munlock(), the function that walks the reverse map to check
341for other VM_LOCKED vmas, without first isolating the page from the LRU.
342try_to_munlock() is a variant of try_to_unmap() and thus requires that the page
343not be on an lru list. [More on these below.] However, the call to
344isolate_lru_page() could fail, in which case we couldn't try_to_munlock().
345So, we go ahead and clear PG_mlocked up front, as this might be the only chance
346we have. If we can successfully isolate the page, we go ahead and
347try_to_munlock(), which will restore the PG_mlocked flag and update the zone
348page statistics if it finds another vma holding the page mlocked. If we fail
349to isolate the page, we'll have left a potentially mlocked page on the LRU.
350This is fine, because we'll catch it later when/if vmscan tries to reclaim the
351page. This should be relatively rare.
352
353Mlocked Pages: Migrating Them...
354
355A page that is being migrated has been isolated from the lru lists and is
356held locked across unmapping of the page, updating the page's mapping
357[address_space] entry and copying the contents and state, until the
358page table entry has been replaced with an entry that refers to the new
359page. Linux supports migration of mlocked pages and other unevictable
360pages. This involves simply moving the PageMlocked and PageUnevictable states
361from the old page to the new page.
362
363Note that page migration can race with mlocking or munlocking of the same
364page. This has been discussed from the mlock/munlock perspective in the
365respective sections above. Both processes [migration, m[un]locking], hold
366the page locked. This provides the first level of synchronization. Page
367migration zeros out the page_mapping of the old page before unlocking it,
368so m[un]lock can skip these pages by testing the page mapping under page
369lock.
370
371When completing page migration, we place the new and old pages back onto the
372lru after dropping the page lock. The "unneeded" page--old page on success,
373new page on failure--will be freed when the reference count held by the
374migration process is released. To ensure that we don't strand pages on the
375unevictable list because of a race between munlock and migration, page
376migration uses the putback_lru_page() function to add migrated pages back to
377the lru.
378
379
380Mlocked Pages: mmap(MAP_LOCKED) System Call Handling
381
382In addition the the mlock()/mlockall() system calls, an application can request
383that a region of memory be mlocked using the MAP_LOCKED flag with the mmap()
384call. Furthermore, any mmap() call or brk() call that expands the heap by a
385task that has previously called mlockall() with the MCL_FUTURE flag will result
386in the newly mapped memory being mlocked. Before the unevictable/mlock changes,
387the kernel simply called make_pages_present() to allocate pages and populate
388the page table.
389
390To mlock a range of memory under the unevictable/mlock infrastructure, the
391mmap() handler and task address space expansion functions call
392mlock_vma_pages_range() specifying the vma and the address range to mlock.
393mlock_vma_pages_range() filters vmas like mlock_fixup(), as described above in
394"Mlocked Pages: Filtering Vmas". It will clear the VM_LOCKED flag, which will
395have already been set by the caller, in filtered vmas. Thus these vma's need
396not be visited for munlock when the region is unmapped.
397
398For "normal" vmas, mlock_vma_pages_range() calls __mlock_vma_pages_range() to
399fault/allocate the pages and mlock them. Again, like mlock_fixup(),
400mlock_vma_pages_range() downgrades the mmap semaphore to read mode before
401attempting to fault/allocate and mlock the pages; and "upgrades" the semaphore
402back to write mode before returning.
403
404The callers of mlock_vma_pages_range() will have already added the memory
405range to be mlocked to the task's "locked_vm". To account for filtered vmas,
406mlock_vma_pages_range() returns the number of pages NOT mlocked. All of the
407callers then subtract a non-negative return value from the task's locked_vm.
408A negative return value represent an error--for example, from get_user_pages()
409attempting to fault in a vma with PROT_NONE access. In this case, we leave
410the memory range accounted as locked_vm, as the protections could be changed
411later and pages allocated into that region.
412
413
414Mlocked Pages: munmap()/exit()/exec() System Call Handling
415
416When unmapping an mlocked region of memory, whether by an explicit call to
417munmap() or via an internal unmap from exit() or exec() processing, we must
418munlock the pages if we're removing the last VM_LOCKED vma that maps the pages.
419Before the unevictable/mlock changes, mlocking did not mark the pages in any way,
420so unmapping them required no processing.
421
422To munlock a range of memory under the unevictable/mlock infrastructure, the
423munmap() hander and task address space tear down function call
424munlock_vma_pages_all(). The name reflects the observation that one always
425specifies the entire vma range when munlock()ing during unmap of a region.
426Because of the vma filtering when mlocking() regions, only "normal" vmas that
427actually contain mlocked pages will be passed to munlock_vma_pages_all().
428
429munlock_vma_pages_all() clears the VM_LOCKED vma flag and, like mlock_fixup()
430for the munlock case, calls __munlock_vma_pages_range() to walk the page table
431for the vma's memory range and munlock_vma_page() each resident page mapped by
432the vma. This effectively munlocks the page, only if this is the last
433VM_LOCKED vma that maps the page.
434
435
436Mlocked Page: try_to_unmap()
437
438[Note: the code changes represented by this section are really quite small
439compared to the text to describe what happening and why, and to discuss the
440implications.]
441
442Pages can, of course, be mapped into multiple vmas. Some of these vmas may
443have VM_LOCKED flag set. It is possible for a page mapped into one or more
444VM_LOCKED vmas not to have the PG_mlocked flag set and therefore reside on one
445of the active or inactive LRU lists. This could happen if, for example, a
446task in the process of munlock()ing the page could not isolate the page from
447the LRU. As a result, vmscan/shrink_page_list() might encounter such a page
448as described in "Unevictable Pages and Vmscan [shrink_*_list()]". To
449handle this situation, try_to_unmap() has been enhanced to check for VM_LOCKED
450vmas while it is walking a page's reverse map.
451
452try_to_unmap() is always called, by either vmscan for reclaim or for page
453migration, with the argument page locked and isolated from the LRU. BUG_ON()
454assertions enforce this requirement. Separate functions handle anonymous and
455mapped file pages, as these types of pages have different reverse map
456mechanisms.
457
458 try_to_unmap_anon()
459
460To unmap anonymous pages, each vma in the list anchored in the anon_vma must be
461visited--at least until a VM_LOCKED vma is encountered. If the page is being
462unmapped for migration, VM_LOCKED vmas do not stop the process because mlocked
463pages are migratable. However, for reclaim, if the page is mapped into a
464VM_LOCKED vma, the scan stops. try_to_unmap() attempts to acquire the mmap
465semphore of the mm_struct to which the vma belongs in read mode. If this is
466successful, try_to_unmap() will mlock the page via mlock_vma_page()--we
467wouldn't have gotten to try_to_unmap() if the page were already mlocked--and
468will return SWAP_MLOCK, indicating that the page is unevictable. If the
469mmap semaphore cannot be acquired, we are not sure whether the page is really
470unevictable or not. In this case, try_to_unmap() will return SWAP_AGAIN.
471
472 try_to_unmap_file() -- linear mappings
473
474Unmapping of a mapped file page works the same, except that the scan visits
475all vmas that maps the page's index/page offset in the page's mapping's
476reverse map priority search tree. It must also visit each vma in the page's
477mapping's non-linear list, if the list is non-empty. As for anonymous pages,
478on encountering a VM_LOCKED vma for a mapped file page, try_to_unmap() will
479attempt to acquire the associated mm_struct's mmap semaphore to mlock the page,
480returning SWAP_MLOCK if this is successful, and SWAP_AGAIN, if not.
481
482 try_to_unmap_file() -- non-linear mappings
483
484If a page's mapping contains a non-empty non-linear mapping vma list, then
485try_to_un{map|lock}() must also visit each vma in that list to determine
486whether the page is mapped in a VM_LOCKED vma. Again, the scan must visit
487all vmas in the non-linear list to ensure that the pages is not/should not be
488mlocked. If a VM_LOCKED vma is found in the list, the scan could terminate.
489However, there is no easy way to determine whether the page is actually mapped
490in a given vma--either for unmapping or testing whether the VM_LOCKED vma
491actually pins the page.
492
493So, try_to_unmap_file() handles non-linear mappings by scanning a certain
494number of pages--a "cluster"--in each non-linear vma associated with the page's
495mapping, for each file mapped page that vmscan tries to unmap. If this happens
496to unmap the page we're trying to unmap, try_to_unmap() will notice this on
497return--(page_mapcount(page) == 0)--and return SWAP_SUCCESS. Otherwise, it
498will return SWAP_AGAIN, causing vmscan to recirculate this page. We take
499advantage of the cluster scan in try_to_unmap_cluster() as follows:
500
501For each non-linear vma, try_to_unmap_cluster() attempts to acquire the mmap
502semaphore of the associated mm_struct for read without blocking. If this
503attempt is successful and the vma is VM_LOCKED, try_to_unmap_cluster() will
504retain the mmap semaphore for the scan; otherwise it drops it here. Then,
505for each page in the cluster, if we're holding the mmap semaphore for a locked
506vma, try_to_unmap_cluster() calls mlock_vma_page() to mlock the page. This
507call is a no-op if the page is already locked, but will mlock any pages in
508the non-linear mapping that happen to be unlocked. If one of the pages so
509mlocked is the page passed in to try_to_unmap(), try_to_unmap_cluster() will
510return SWAP_MLOCK, rather than the default SWAP_AGAIN. This will allow vmscan
511to cull the page, rather than recirculating it on the inactive list. Again,
512if try_to_unmap_cluster() cannot acquire the vma's mmap sem, it returns
513SWAP_AGAIN, indicating that the page is mapped by a VM_LOCKED vma, but
514couldn't be mlocked.
515
516
517Mlocked pages: try_to_munlock() Reverse Map Scan
518
519TODO/FIXME: a better name might be page_mlocked()--analogous to the
520page_referenced() reverse map walker--especially if we continue to call this
521from shrink_page_list(). See related TODO/FIXME below.
522
523When munlock_vma_page()--see "Mlocked Pages: munlock()/munlockall() System
524Call Handling" above--tries to munlock a page, or when shrink_page_list()
525encounters an anonymous page that is not yet in the swap cache, they need to
526determine whether or not the page is mapped by any VM_LOCKED vma, without
527actually attempting to unmap all ptes from the page. For this purpose, the
528unevictable/mlock infrastructure introduced a variant of try_to_unmap() called
529try_to_munlock().
530
531try_to_munlock() calls the same functions as try_to_unmap() for anonymous and
532mapped file pages with an additional argument specifing unlock versus unmap
533processing. Again, these functions walk the respective reverse maps looking
534for VM_LOCKED vmas. When such a vma is found for anonymous pages and file
535pages mapped in linear VMAs, as in the try_to_unmap() case, the functions
536attempt to acquire the associated mmap semphore, mlock the page via
537mlock_vma_page() and return SWAP_MLOCK. This effectively undoes the
538pre-clearing of the page's PG_mlocked done by munlock_vma_page() and informs
539shrink_page_list() that the anonymous page should be culled rather than added
540to the swap cache in preparation for a try_to_unmap() that will almost
541certainly fail.
542
543If try_to_unmap() is unable to acquire a VM_LOCKED vma's associated mmap
544semaphore, it will return SWAP_AGAIN. This will allow shrink_page_list()
545to recycle the page on the inactive list and hope that it has better luck
546with the page next time.
547
548For file pages mapped into non-linear vmas, the try_to_munlock() logic works
549slightly differently. On encountering a VM_LOCKED non-linear vma that might
550map the page, try_to_munlock() returns SWAP_AGAIN without actually mlocking
551the page. munlock_vma_page() will just leave the page unlocked and let
552vmscan deal with it--the usual fallback position.
553
554Note that try_to_munlock()'s reverse map walk must visit every vma in a pages'
555reverse map to determine that a page is NOT mapped into any VM_LOCKED vma.
556However, the scan can terminate when it encounters a VM_LOCKED vma and can
557successfully acquire the vma's mmap semphore for read and mlock the page.
558Although try_to_munlock() can be called many [very many!] times when
559munlock()ing a large region or tearing down a large address space that has been
560mlocked via mlockall(), overall this is a fairly rare event. In addition,
561although shrink_page_list() calls try_to_munlock() for every anonymous page that
562it handles that is not yet in the swap cache, on average anonymous pages will
563have very short reverse map lists.
564
565Mlocked Page: Page Reclaim in shrink_*_list()
566
567shrink_active_list() culls any obviously unevictable pages--i.e.,
568!page_evictable(page, NULL)--diverting these to the unevictable lru
569list. However, shrink_active_list() only sees unevictable pages that
570made it onto the active/inactive lru lists. Note that these pages do not
571have PageUnevictable set--otherwise, they would be on the unevictable list and
572shrink_active_list would never see them.
573
574Some examples of these unevictable pages on the LRU lists are:
575
5761) ramfs pages that have been placed on the lru lists when first allocated.
577
5782) SHM_LOCKed shared memory pages. shmctl(SHM_LOCK) does not attempt to
579 allocate or fault in the pages in the shared memory region. This happens
580 when an application accesses the page the first time after SHM_LOCKing
581 the segment.
582
5833) Mlocked pages that could not be isolated from the lru and moved to the
584 unevictable list in mlock_vma_page().
585
5863) Pages mapped into multiple VM_LOCKED vmas, but try_to_munlock() couldn't
587 acquire the vma's mmap semaphore to test the flags and set PageMlocked.
588 munlock_vma_page() was forced to let the page back on to the normal
589 LRU list for vmscan to handle.
590
591shrink_inactive_list() also culls any unevictable pages that it finds
592on the inactive lists, again diverting them to the appropriate zone's unevictable
593lru list. shrink_inactive_list() should only see SHM_LOCKed pages that became
594SHM_LOCKed after shrink_active_list() had moved them to the inactive list, or
595pages mapped into VM_LOCKED vmas that munlock_vma_page() couldn't isolate from
596the lru to recheck via try_to_munlock(). shrink_inactive_list() won't notice
597the latter, but will pass on to shrink_page_list().
598
599shrink_page_list() again culls obviously unevictable pages that it could
600encounter for similar reason to shrink_inactive_list(). As already discussed,
601shrink_page_list() proactively looks for anonymous pages that should have
602PG_mlocked set but don't--these would not be detected by page_evictable()--to
603avoid adding them to the swap cache unnecessarily. File pages mapped into
604VM_LOCKED vmas but without PG_mlocked set will make it all the way to
605try_to_unmap(). shrink_page_list() will divert them to the unevictable list when
606try_to_unmap() returns SWAP_MLOCK, as discussed above.
607
608TODO/FIXME: If we can enhance the swap cache to reliably remove entries
609with page_count(page) > 2, as long as all ptes are mapped to the page and
610not the swap entry, we can probably remove the call to try_to_munlock() in
611shrink_page_list() and just remove the page from the swap cache when
612try_to_unmap() returns SWAP_MLOCK. Currently, remove_exclusive_swap_page()
613doesn't seem to allow that.
614
615