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authorLi Zefan <lizf@cn.fujitsu.com>2009-01-15 16:50:59 -0500
committerLinus Torvalds <torvalds@linux-foundation.org>2009-01-15 19:39:37 -0500
commit45ce80fb6b6f9594d1396d44dd7e7c02d596fef8 (patch)
tree2409270f7073c08329ac01c82df0509a264af48c /Documentation/cgroups
parent23964d2d02984d44aeb2d84d7ffb3359e728df43 (diff)
cgroups: consolidate cgroup documents
Move Documentation/cpusets.txt and Documentation/controllers/* to Documentation/cgroups/ Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com> Acked-by: Paul Menage <menage@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/cgroups')
-rw-r--r--Documentation/cgroups/cgroups.txt5
-rw-r--r--Documentation/cgroups/cpuacct.txt32
-rw-r--r--Documentation/cgroups/cpusets.txt808
-rw-r--r--Documentation/cgroups/devices.txt52
-rw-r--r--Documentation/cgroups/memcg_test.txt342
-rw-r--r--Documentation/cgroups/memory.txt399
-rw-r--r--Documentation/cgroups/resource_counter.txt181
7 files changed, 1817 insertions, 2 deletions
diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index e33ee74eee77..d9e5d6f41b92 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -1,7 +1,8 @@
1 CGROUPS 1 CGROUPS
2 ------- 2 -------
3 3
4Written by Paul Menage <menage@google.com> based on Documentation/cpusets.txt 4Written by Paul Menage <menage@google.com> based on
5Documentation/cgroups/cpusets.txt
5 6
6Original copyright statements from cpusets.txt: 7Original copyright statements from cpusets.txt:
7Portions Copyright (C) 2004 BULL SA. 8Portions Copyright (C) 2004 BULL SA.
@@ -68,7 +69,7 @@ On their own, the only use for cgroups is for simple job
68tracking. The intention is that other subsystems hook into the generic 69tracking. The intention is that other subsystems hook into the generic
69cgroup support to provide new attributes for cgroups, such as 70cgroup support to provide new attributes for cgroups, such as
70accounting/limiting the resources which processes in a cgroup can 71accounting/limiting the resources which processes in a cgroup can
71access. For example, cpusets (see Documentation/cpusets.txt) allows 72access. For example, cpusets (see Documentation/cgroups/cpusets.txt) allows
72you to associate a set of CPUs and a set of memory nodes with the 73you to associate a set of CPUs and a set of memory nodes with the
73tasks in each cgroup. 74tasks in each cgroup.
74 75
diff --git a/Documentation/cgroups/cpuacct.txt b/Documentation/cgroups/cpuacct.txt
new file mode 100644
index 000000000000..bb775fbe43d7
--- /dev/null
+++ b/Documentation/cgroups/cpuacct.txt
@@ -0,0 +1,32 @@
1CPU Accounting Controller
2-------------------------
3
4The CPU accounting controller is used to group tasks using cgroups and
5account the CPU usage of these groups of tasks.
6
7The CPU accounting controller supports multi-hierarchy groups. An accounting
8group accumulates the CPU usage of all of its child groups and the tasks
9directly present in its group.
10
11Accounting groups can be created by first mounting the cgroup filesystem.
12
13# mkdir /cgroups
14# mount -t cgroup -ocpuacct none /cgroups
15
16With the above step, the initial or the parent accounting group
17becomes visible at /cgroups. At bootup, this group includes all the
18tasks in the system. /cgroups/tasks lists the tasks in this cgroup.
19/cgroups/cpuacct.usage gives the CPU time (in nanoseconds) obtained by
20this group which is essentially the CPU time obtained by all the tasks
21in the system.
22
23New accounting groups can be created under the parent group /cgroups.
24
25# cd /cgroups
26# mkdir g1
27# echo $$ > g1
28
29The above steps create a new group g1 and move the current shell
30process (bash) into it. CPU time consumed by this bash and its children
31can be obtained from g1/cpuacct.usage and the same is accumulated in
32/cgroups/cpuacct.usage also.
diff --git a/Documentation/cgroups/cpusets.txt b/Documentation/cgroups/cpusets.txt
new file mode 100644
index 000000000000..5c86c258c791
--- /dev/null
+++ b/Documentation/cgroups/cpusets.txt
@@ -0,0 +1,808 @@
1 CPUSETS
2 -------
3
4Copyright (C) 2004 BULL SA.
5Written by Simon.Derr@bull.net
6
7Portions Copyright (c) 2004-2006 Silicon Graphics, Inc.
8Modified by Paul Jackson <pj@sgi.com>
9Modified by Christoph Lameter <clameter@sgi.com>
10Modified by Paul Menage <menage@google.com>
11Modified by Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
12
13CONTENTS:
14=========
15
161. Cpusets
17 1.1 What are cpusets ?
18 1.2 Why are cpusets needed ?
19 1.3 How are cpusets implemented ?
20 1.4 What are exclusive cpusets ?
21 1.5 What is memory_pressure ?
22 1.6 What is memory spread ?
23 1.7 What is sched_load_balance ?
24 1.8 What is sched_relax_domain_level ?
25 1.9 How do I use cpusets ?
262. Usage Examples and Syntax
27 2.1 Basic Usage
28 2.2 Adding/removing cpus
29 2.3 Setting flags
30 2.4 Attaching processes
313. Questions
324. Contact
33
341. Cpusets
35==========
36
371.1 What are cpusets ?
38----------------------
39
40Cpusets provide a mechanism for assigning a set of CPUs and Memory
41Nodes to a set of tasks. In this document "Memory Node" refers to
42an on-line node that contains memory.
43
44Cpusets constrain the CPU and Memory placement of tasks to only
45the resources within a tasks current cpuset. They form a nested
46hierarchy visible in a virtual file system. These are the essential
47hooks, beyond what is already present, required to manage dynamic
48job placement on large systems.
49
50Cpusets use the generic cgroup subsystem described in
51Documentation/cgroups/cgroups.txt.
52
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
55set_mempolicy(2) system calls to include Memory Nodes in its memory
56policy, are both filtered through that tasks cpuset, filtering out any
57CPUs or Memory Nodes not in that cpuset. The scheduler will not
58schedule a task on a CPU that is not allowed in its cpus_allowed
59vector, and the kernel page allocator will not allocate a page on a
60node that is not allowed in the requesting tasks mems_allowed vector.
61
62User level code may create and destroy cpusets by name in the cgroup
63virtual file system, manage the attributes and permissions of these
64cpusets and which CPUs and Memory Nodes are assigned to each cpuset,
65specify and query to which cpuset a task is assigned, and list the
66task pids assigned to a cpuset.
67
68
691.2 Why are cpusets needed ?
70----------------------------
71
72The management of large computer systems, with many processors (CPUs),
73complex memory cache hierarchies and multiple Memory Nodes having
74non-uniform access times (NUMA) presents additional challenges for
75the efficient scheduling and memory placement of processes.
76
77Frequently more modest sized systems can be operated with adequate
78efficiency just by letting the operating system automatically share
79the available CPU and Memory resources amongst the requesting tasks.
80
81But larger systems, which benefit more from careful processor and
82memory placement to reduce memory access times and contention,
83and which typically represent a larger investment for the customer,
84can benefit from explicitly placing jobs on properly sized subsets of
85the system.
86
87This can be especially valuable on:
88
89 * Web Servers running multiple instances of the same web application,
90 * Servers running different applications (for instance, a web server
91 and a database), or
92 * NUMA systems running large HPC applications with demanding
93 performance characteristics.
94
95These subsets, or "soft partitions" must be able to be dynamically
96adjusted, as the job mix changes, without impacting other concurrently
97executing jobs. The location of the running jobs pages may also be moved
98when the memory locations are changed.
99
100The kernel cpuset patch provides the minimum essential kernel
101mechanisms required to efficiently implement such subsets. It
102leverages existing CPU and Memory Placement facilities in the Linux
103kernel to avoid any additional impact on the critical scheduler or
104memory allocator code.
105
106
1071.3 How are cpusets implemented ?
108---------------------------------
109
110Cpusets provide a Linux kernel mechanism to constrain which CPUs and
111Memory Nodes are used by a process or set of processes.
112
113The Linux kernel already has a pair of mechanisms to specify on which
114CPUs a task may be scheduled (sched_setaffinity) and on which Memory
115Nodes it may obtain memory (mbind, set_mempolicy).
116
117Cpusets extends these two mechanisms as follows:
118
119 - Cpusets are sets of allowed CPUs and Memory Nodes, known to the
120 kernel.
121 - Each task in the system is attached to a cpuset, via a pointer
122 in the task structure to a reference counted cgroup structure.
123 - Calls to sched_setaffinity are filtered to just those CPUs
124 allowed in that tasks cpuset.
125 - Calls to mbind and set_mempolicy are filtered to just
126 those Memory Nodes allowed in that tasks cpuset.
127 - The root cpuset contains all the systems CPUs and Memory
128 Nodes.
129 - For any cpuset, one can define child cpusets containing a subset
130 of the parents CPU and Memory Node resources.
131 - The hierarchy of cpusets can be mounted at /dev/cpuset, for
132 browsing and manipulation from user space.
133 - A cpuset may be marked exclusive, which ensures that no other
134 cpuset (except direct ancestors and descendents) may contain
135 any overlapping CPUs or Memory Nodes.
136 - You can list all the tasks (by pid) attached to any cpuset.
137
138The implementation of cpusets requires a few, simple hooks
139into the rest of the kernel, none in performance critical paths:
140
141 - in init/main.c, to initialize the root cpuset at system boot.
142 - in fork and exit, to attach and detach a task from its cpuset.
143 - in sched_setaffinity, to mask the requested CPUs by what's
144 allowed in that tasks cpuset.
145 - in sched.c migrate_all_tasks(), to keep migrating tasks within
146 the CPUs allowed by their cpuset, if possible.
147 - in the mbind and set_mempolicy system calls, to mask the requested
148 Memory Nodes by what's allowed in that tasks cpuset.
149 - in page_alloc.c, to restrict memory to allowed nodes.
150 - in vmscan.c, to restrict page recovery to the current cpuset.
151
152You should mount the "cgroup" filesystem type in order to enable
153browsing and modifying the cpusets presently known to the kernel. No
154new system calls are added for cpusets - all support for querying and
155modifying cpusets is via this cpuset file system.
156
157The /proc/<pid>/status file for each task has four added lines,
158displaying the tasks cpus_allowed (on which CPUs it may be scheduled)
159and mems_allowed (on which Memory Nodes it may obtain memory),
160in the two formats seen in the following example:
161
162 Cpus_allowed: ffffffff,ffffffff,ffffffff,ffffffff
163 Cpus_allowed_list: 0-127
164 Mems_allowed: ffffffff,ffffffff
165 Mems_allowed_list: 0-63
166
167Each cpuset is represented by a directory in the cgroup file system
168containing (on top of the standard cgroup files) the following
169files describing that cpuset:
170
171 - cpus: list of CPUs in that cpuset
172 - mems: list of Memory Nodes in that cpuset
173 - memory_migrate flag: if set, move pages to cpusets nodes
174 - cpu_exclusive flag: is cpu placement exclusive?
175 - mem_exclusive flag: is memory placement exclusive?
176 - mem_hardwall flag: is memory allocation hardwalled
177 - memory_pressure: measure of how much paging pressure in cpuset
178
179In addition, the root cpuset only has the following file:
180 - memory_pressure_enabled flag: compute memory_pressure?
181
182New cpusets are created using the mkdir system call or shell
183command. The properties of a cpuset, such as its flags, allowed
184CPUs and Memory Nodes, and attached tasks, are modified by writing
185to the appropriate file in that cpusets directory, as listed above.
186
187The named hierarchical structure of nested cpusets allows partitioning
188a large system into nested, dynamically changeable, "soft-partitions".
189
190The attachment of each task, automatically inherited at fork by any
191children of that task, to a cpuset allows organizing the work load
192on a system into related sets of tasks such that each set is constrained
193to using the CPUs and Memory Nodes of a particular cpuset. A task
194may be re-attached to any other cpuset, if allowed by the permissions
195on the necessary cpuset file system directories.
196
197Such management of a system "in the large" integrates smoothly with
198the detailed placement done on individual tasks and memory regions
199using the sched_setaffinity, mbind and set_mempolicy system calls.
200
201The following rules apply to each cpuset:
202
203 - Its CPUs and Memory Nodes must be a subset of its parents.
204 - It can't be marked exclusive unless its parent is.
205 - If its cpu or memory is exclusive, they may not overlap any sibling.
206
207These rules, and the natural hierarchy of cpusets, enable efficient
208enforcement of the exclusive guarantee, without having to scan all
209cpusets every time any of them change to ensure nothing overlaps a
210exclusive cpuset. Also, the use of a Linux virtual file system (vfs)
211to represent the cpuset hierarchy provides for a familiar permission
212and name space for cpusets, with a minimum of additional kernel code.
213
214The cpus and mems files in the root (top_cpuset) cpuset are
215read-only. The cpus file automatically tracks the value of
216cpu_online_map using a CPU hotplug notifier, and the mems file
217automatically tracks the value of node_states[N_HIGH_MEMORY]--i.e.,
218nodes with memory--using the cpuset_track_online_nodes() hook.
219
220
2211.4 What are exclusive cpusets ?
222--------------------------------
223
224If a cpuset is cpu or mem exclusive, no other cpuset, other than
225a direct ancestor or descendent, may share any of the same CPUs or
226Memory Nodes.
227
228A cpuset that is mem_exclusive *or* mem_hardwall is "hardwalled",
229i.e. it restricts kernel allocations for page, buffer and other data
230commonly shared by the kernel across multiple users. All cpusets,
231whether hardwalled or not, restrict allocations of memory for user
232space. This enables configuring a system so that several independent
233jobs can share common kernel data, such as file system pages, while
234isolating each job's user allocation in its own cpuset. To do this,
235construct a large mem_exclusive cpuset to hold all the jobs, and
236construct child, non-mem_exclusive cpusets for each individual job.
237Only a small amount of typical kernel memory, such as requests from
238interrupt handlers, is allowed to be taken outside even a
239mem_exclusive cpuset.
240
241
2421.5 What is memory_pressure ?
243-----------------------------
244The memory_pressure of a cpuset provides a simple per-cpuset metric
245of the rate that the tasks in a cpuset are attempting to free up in
246use memory on the nodes of the cpuset to satisfy additional memory
247requests.
248
249This enables batch managers monitoring jobs running in dedicated
250cpusets to efficiently detect what level of memory pressure that job
251is causing.
252
253This is useful both on tightly managed systems running a wide mix of
254submitted jobs, which may choose to terminate or re-prioritize jobs that
255are trying to use more memory than allowed on the nodes assigned them,
256and with tightly coupled, long running, massively parallel scientific
257computing jobs that will dramatically fail to meet required performance
258goals if they start to use more memory than allowed to them.
259
260This mechanism provides a very economical way for the batch manager
261to monitor a cpuset for signs of memory pressure. It's up to the
262batch manager or other user code to decide what to do about it and
263take action.
264
265==> Unless this feature is enabled by writing "1" to the special file
266 /dev/cpuset/memory_pressure_enabled, the hook in the rebalance
267 code of __alloc_pages() for this metric reduces to simply noticing
268 that the cpuset_memory_pressure_enabled flag is zero. So only
269 systems that enable this feature will compute the metric.
270
271Why a per-cpuset, running average:
272
273 Because this meter is per-cpuset, rather than per-task or mm,
274 the system load imposed by a batch scheduler monitoring this
275 metric is sharply reduced on large systems, because a scan of
276 the tasklist can be avoided on each set of queries.
277
278 Because this meter is a running average, instead of an accumulating
279 counter, a batch scheduler can detect memory pressure with a
280 single read, instead of having to read and accumulate results
281 for a period of time.
282
283 Because this meter is per-cpuset rather than per-task or mm,
284 the batch scheduler can obtain the key information, memory
285 pressure in a cpuset, with a single read, rather than having to
286 query and accumulate results over all the (dynamically changing)
287 set of tasks in the cpuset.
288
289A per-cpuset simple digital filter (requires a spinlock and 3 words
290of data per-cpuset) is kept, and updated by any task attached to that
291cpuset, if it enters the synchronous (direct) page reclaim code.
292
293A per-cpuset file provides an integer number representing the recent
294(half-life of 10 seconds) rate of direct page reclaims caused by
295the tasks in the cpuset, in units of reclaims attempted per second,
296times 1000.
297
298
2991.6 What is memory spread ?
300---------------------------
301There are two boolean flag files per cpuset that control where the
302kernel allocates pages for the file system buffers and related in
303kernel data structures. They are called 'memory_spread_page' and
304'memory_spread_slab'.
305
306If the per-cpuset boolean flag file 'memory_spread_page' is set, then
307the kernel will spread the file system buffers (page cache) evenly
308over all the nodes that the faulting task is allowed to use, instead
309of preferring to put those pages on the node where the task is running.
310
311If the per-cpuset boolean flag file 'memory_spread_slab' is set,
312then the kernel will spread some file system related slab caches,
313such as for inodes and dentries evenly over all the nodes that the
314faulting task is allowed to use, instead of preferring to put those
315pages on the node where the task is running.
316
317The setting of these flags does not affect anonymous data segment or
318stack segment pages of a task.
319
320By default, both kinds of memory spreading are off, and memory
321pages are allocated on the node local to where the task is running,
322except perhaps as modified by the tasks NUMA mempolicy or cpuset
323configuration, so long as sufficient free memory pages are available.
324
325When new cpusets are created, they inherit the memory spread settings
326of their parent.
327
328Setting memory spreading causes allocations for the affected page
329or slab caches to ignore the tasks NUMA mempolicy and be spread
330instead. Tasks using mbind() or set_mempolicy() calls to set NUMA
331mempolicies will not notice any change in these calls as a result of
332their containing tasks memory spread settings. If memory spreading
333is turned off, then the currently specified NUMA mempolicy once again
334applies to memory page allocations.
335
336Both 'memory_spread_page' and 'memory_spread_slab' are boolean flag
337files. By default they contain "0", meaning that the feature is off
338for that cpuset. If a "1" is written to that file, then that turns
339the named feature on.
340
341The implementation is simple.
342
343Setting the flag 'memory_spread_page' turns on a per-process flag
344PF_SPREAD_PAGE for each task that is in that cpuset or subsequently
345joins that cpuset. The page allocation calls for the page cache
346is modified to perform an inline check for this PF_SPREAD_PAGE task
347flag, and if set, a call to a new routine cpuset_mem_spread_node()
348returns the node to prefer for the allocation.
349
350Similarly, setting 'memory_spread_slab' turns on the flag
351PF_SPREAD_SLAB, and appropriately marked slab caches will allocate
352pages from the node returned by cpuset_mem_spread_node().
353
354The cpuset_mem_spread_node() routine is also simple. It uses the
355value of a per-task rotor cpuset_mem_spread_rotor to select the next
356node in the current tasks mems_allowed to prefer for the allocation.
357
358This memory placement policy is also known (in other contexts) as
359round-robin or interleave.
360
361This policy can provide substantial improvements for jobs that need
362to place thread local data on the corresponding node, but that need
363to access large file system data sets that need to be spread across
364the several nodes in the jobs cpuset in order to fit. Without this
365policy, especially for jobs that might have one thread reading in the
366data set, the memory allocation across the nodes in the jobs cpuset
367can become very uneven.
368
3691.7 What is sched_load_balance ?
370--------------------------------
371
372The kernel scheduler (kernel/sched.c) automatically load balances
373tasks. If one CPU is underutilized, kernel code running on that
374CPU will look for tasks on other more overloaded CPUs and move those
375tasks to itself, within the constraints of such placement mechanisms
376as cpusets and sched_setaffinity.
377
378The algorithmic cost of load balancing and its impact on key shared
379kernel data structures such as the task list increases more than
380linearly with the number of CPUs being balanced. So the scheduler
381has support to partition the systems CPUs into a number of sched
382domains such that it only load balances within each sched domain.
383Each sched domain covers some subset of the CPUs in the system;
384no two sched domains overlap; some CPUs might not be in any sched
385domain and hence won't be load balanced.
386
387Put simply, it costs less to balance between two smaller sched domains
388than one big one, but doing so means that overloads in one of the
389two domains won't be load balanced to the other one.
390
391By default, there is one sched domain covering all CPUs, except those
392marked isolated using the kernel boot time "isolcpus=" argument.
393
394This default load balancing across all CPUs is not well suited for
395the following two situations:
396 1) On large systems, load balancing across many CPUs is expensive.
397 If the system is managed using cpusets to place independent jobs
398 on separate sets of CPUs, full load balancing is unnecessary.
399 2) Systems supporting realtime on some CPUs need to minimize
400 system overhead on those CPUs, including avoiding task load
401 balancing if that is not needed.
402
403When the per-cpuset flag "sched_load_balance" is enabled (the default
404setting), it requests that all the CPUs in that cpusets allowed 'cpus'
405be contained in a single sched domain, ensuring that load balancing
406can move a task (not otherwised pinned, as by sched_setaffinity)
407from any CPU in that cpuset to any other.
408
409When the per-cpuset flag "sched_load_balance" is disabled, then the
410scheduler will avoid load balancing across the CPUs in that cpuset,
411--except-- in so far as is necessary because some overlapping cpuset
412has "sched_load_balance" enabled.
413
414So, for example, if the top cpuset has the flag "sched_load_balance"
415enabled, then the scheduler will have one sched domain covering all
416CPUs, and the setting of the "sched_load_balance" flag in any other
417cpusets won't matter, as we're already fully load balancing.
418
419Therefore in the above two situations, the top cpuset flag
420"sched_load_balance" should be disabled, and only some of the smaller,
421child cpusets have this flag enabled.
422
423When doing this, you don't usually want to leave any unpinned tasks in
424the top cpuset that might use non-trivial amounts of CPU, as such tasks
425may be artificially constrained to some subset of CPUs, depending on
426the particulars of this flag setting in descendent cpusets. Even if
427such a task could use spare CPU cycles in some other CPUs, the kernel
428scheduler might not consider the possibility of load balancing that
429task to that underused CPU.
430
431Of course, tasks pinned to a particular CPU can be left in a cpuset
432that disables "sched_load_balance" as those tasks aren't going anywhere
433else anyway.
434
435There is an impedance mismatch here, between cpusets and sched domains.
436Cpusets are hierarchical and nest. Sched domains are flat; they don't
437overlap and each CPU is in at most one sched domain.
438
439It is necessary for sched domains to be flat because load balancing
440across partially overlapping sets of CPUs would risk unstable dynamics
441that would be beyond our understanding. So if each of two partially
442overlapping cpusets enables the flag 'sched_load_balance', then we
443form a single sched domain that is a superset of both. We won't move
444a task to a CPU outside it cpuset, but the scheduler load balancing
445code might waste some compute cycles considering that possibility.
446
447This mismatch is why there is not a simple one-to-one relation
448between which cpusets have the flag "sched_load_balance" enabled,
449and the sched domain configuration. If a cpuset enables the flag, it
450will get balancing across all its CPUs, but if it disables the flag,
451it will only be assured of no load balancing if no other overlapping
452cpuset enables the flag.
453
454If two cpusets have partially overlapping 'cpus' allowed, and only
455one of them has this flag enabled, then the other may find its
456tasks only partially load balanced, just on the overlapping CPUs.
457This is just the general case of the top_cpuset example given a few
458paragraphs above. In the general case, as in the top cpuset case,
459don't leave tasks that might use non-trivial amounts of CPU in
460such partially load balanced cpusets, as they may be artificially
461constrained to some subset of the CPUs allowed to them, for lack of
462load balancing to the other CPUs.
463
4641.7.1 sched_load_balance implementation details.
465------------------------------------------------
466
467The per-cpuset flag 'sched_load_balance' defaults to enabled (contrary
468to most cpuset flags.) When enabled for a cpuset, the kernel will
469ensure that it can load balance across all the CPUs in that cpuset
470(makes sure that all the CPUs in the cpus_allowed of that cpuset are
471in the same sched domain.)
472
473If two overlapping cpusets both have 'sched_load_balance' enabled,
474then they will be (must be) both in the same sched domain.
475
476If, as is the default, the top cpuset has 'sched_load_balance' enabled,
477then by the above that means there is a single sched domain covering
478the whole system, regardless of any other cpuset settings.
479
480The kernel commits to user space that it will avoid load balancing
481where it can. It will pick as fine a granularity partition of sched
482domains as it can while still providing load balancing for any set
483of CPUs allowed to a cpuset having 'sched_load_balance' enabled.
484
485The internal kernel cpuset to scheduler interface passes from the
486cpuset code to the scheduler code a partition of the load balanced
487CPUs in the system. This partition is a set of subsets (represented
488as an array of cpumask_t) of CPUs, pairwise disjoint, that cover all
489the CPUs that must be load balanced.
490
491Whenever the 'sched_load_balance' flag changes, or CPUs come or go
492from a cpuset with this flag enabled, or a cpuset with this flag
493enabled is removed, the cpuset code builds a new such partition and
494passes it to the scheduler sched domain setup code, to have the sched
495domains rebuilt as necessary.
496
497This partition exactly defines what sched domains the scheduler should
498setup - one sched domain for each element (cpumask_t) in the partition.
499
500The scheduler remembers the currently active sched domain partitions.
501When the scheduler routine partition_sched_domains() is invoked from
502the cpuset code to update these sched domains, it compares the new
503partition requested with the current, and updates its sched domains,
504removing the old and adding the new, for each change.
505
506
5071.8 What is sched_relax_domain_level ?
508--------------------------------------
509
510In sched domain, the scheduler migrates tasks in 2 ways; periodic load
511balance on tick, and at time of some schedule events.
512
513When a task is woken up, scheduler try to move the task on idle CPU.
514For example, if a task A running on CPU X activates another task B
515on the same CPU X, and if CPU Y is X's sibling and performing idle,
516then scheduler migrate task B to CPU Y so that task B can start on
517CPU Y without waiting task A on CPU X.
518
519And if a CPU run out of tasks in its runqueue, the CPU try to pull
520extra tasks from other busy CPUs to help them before it is going to
521be idle.
522
523Of course it takes some searching cost to find movable tasks and/or
524idle CPUs, the scheduler might not search all CPUs in the domain
525everytime. In fact, in some architectures, the searching ranges on
526events are limited in the same socket or node where the CPU locates,
527while the load balance on tick searchs all.
528
529For example, assume CPU Z is relatively far from CPU X. Even if CPU Z
530is idle while CPU X and the siblings are busy, scheduler can't migrate
531woken task B from X to Z since it is out of its searching range.
532As the result, task B on CPU X need to wait task A or wait load balance
533on the next tick. For some applications in special situation, waiting
5341 tick may be too long.
535
536The 'sched_relax_domain_level' file allows you to request changing
537this searching range as you like. This file takes int value which
538indicates size of searching range in levels ideally as follows,
539otherwise initial value -1 that indicates the cpuset has no request.
540
541 -1 : no request. use system default or follow request of others.
542 0 : no search.
543 1 : search siblings (hyperthreads in a core).
544 2 : search cores in a package.
545 3 : search cpus in a node [= system wide on non-NUMA system]
546 ( 4 : search nodes in a chunk of node [on NUMA system] )
547 ( 5 : search system wide [on NUMA system] )
548
549The system default is architecture dependent. The system default
550can be changed using the relax_domain_level= boot parameter.
551
552This file is per-cpuset and affect the sched domain where the cpuset
553belongs to. Therefore if the flag 'sched_load_balance' of a cpuset
554is disabled, then 'sched_relax_domain_level' have no effect since
555there is no sched domain belonging the cpuset.
556
557If multiple cpusets are overlapping and hence they form a single sched
558domain, the largest value among those is used. Be careful, if one
559requests 0 and others are -1 then 0 is used.
560
561Note that modifying this file will have both good and bad effects,
562and whether it is acceptable or not will be depend on your situation.
563Don't modify this file if you are not sure.
564
565If your situation is:
566 - The migration costs between each cpu can be assumed considerably
567 small(for you) due to your special application's behavior or
568 special hardware support for CPU cache etc.
569 - The searching cost doesn't have impact(for you) or you can make
570 the searching cost enough small by managing cpuset to compact etc.
571 - The latency is required even it sacrifices cache hit rate etc.
572then increasing 'sched_relax_domain_level' would benefit you.
573
574
5751.9 How do I use cpusets ?
576--------------------------
577
578In order to minimize the impact of cpusets on critical kernel
579code, such as the scheduler, and due to the fact that the kernel
580does not support one task updating the memory placement of another
581task directly, the impact on a task of changing its cpuset CPU
582or Memory Node placement, or of changing to which cpuset a task
583is attached, is subtle.
584
585If a cpuset has its Memory Nodes modified, then for each task attached
586to that cpuset, the next time that the kernel attempts to allocate
587a page of memory for that task, the kernel will notice the change
588in the tasks cpuset, and update its per-task memory placement to
589remain within the new cpusets memory placement. If the task was using
590mempolicy MPOL_BIND, and the nodes to which it was bound overlap with
591its new cpuset, then the task will continue to use whatever subset
592of MPOL_BIND nodes are still allowed in the new cpuset. If the task
593was using MPOL_BIND and now none of its MPOL_BIND nodes are allowed
594in the new cpuset, then the task will be essentially treated as if it
595was MPOL_BIND bound to the new cpuset (even though its numa placement,
596as queried by get_mempolicy(), doesn't change). If a task is moved
597from one cpuset to another, then the kernel will adjust the tasks
598memory placement, as above, the next time that the kernel attempts
599to allocate a page of memory for that task.
600
601If a cpuset has its 'cpus' modified, then each task in that cpuset
602will have its allowed CPU placement changed immediately. Similarly,
603if a tasks pid is written to a cpusets 'tasks' file, in either its
604current cpuset or another cpuset, then its allowed CPU placement is
605changed immediately. If such a task had been bound to some subset
606of its cpuset using the sched_setaffinity() call, the task will be
607allowed to run on any CPU allowed in its new cpuset, negating the
608affect of the prior sched_setaffinity() call.
609
610In summary, the memory placement of a task whose cpuset is changed is
611updated by the kernel, on the next allocation of a page for that task,
612but the processor placement is not updated, until that tasks pid is
613rewritten to the 'tasks' file of its cpuset. This is done to avoid
614impacting the scheduler code in the kernel with a check for changes
615in a tasks processor placement.
616
617Normally, once a page is allocated (given a physical page
618of main memory) then that page stays on whatever node it
619was allocated, so long as it remains allocated, even if the
620cpusets memory placement policy 'mems' subsequently changes.
621If the cpuset flag file 'memory_migrate' is set true, then when
622tasks are attached to that cpuset, any pages that task had
623allocated to it on nodes in its previous cpuset are migrated
624to the tasks new cpuset. The relative placement of the page within
625the cpuset is preserved during these migration operations if possible.
626For example if the page was on the second valid node of the prior cpuset
627then the page will be placed on the second valid node of the new cpuset.
628
629Also if 'memory_migrate' is set true, then if that cpusets
630'mems' file is modified, pages allocated to tasks in that
631cpuset, that were on nodes in the previous setting of 'mems',
632will be moved to nodes in the new setting of 'mems.'
633Pages that were not in the tasks prior cpuset, or in the cpusets
634prior 'mems' setting, will not be moved.
635
636There is an exception to the above. If hotplug functionality is used
637to remove all the CPUs that are currently assigned to a cpuset,
638then all the tasks in that cpuset will be moved to the nearest ancestor
639with non-empty cpus. But the moving of some (or all) tasks might fail if
640cpuset is bound with another cgroup subsystem which has some restrictions
641on task attaching. In this failing case, those tasks will stay
642in the original cpuset, and the kernel will automatically update
643their cpus_allowed to allow all online CPUs. When memory hotplug
644functionality for removing Memory Nodes is available, a similar exception
645is expected to apply there as well. In general, the kernel prefers to
646violate cpuset placement, over starving a task that has had all
647its allowed CPUs or Memory Nodes taken offline.
648
649There is a second exception to the above. GFP_ATOMIC requests are
650kernel internal allocations that must be satisfied, immediately.
651The kernel may drop some request, in rare cases even panic, if a
652GFP_ATOMIC alloc fails. If the request cannot be satisfied within
653the current tasks cpuset, then we relax the cpuset, and look for
654memory anywhere we can find it. It's better to violate the cpuset
655than stress the kernel.
656
657To start a new job that is to be contained within a cpuset, the steps are:
658
659 1) mkdir /dev/cpuset
660 2) mount -t cgroup -ocpuset cpuset /dev/cpuset
661 3) Create the new cpuset by doing mkdir's and write's (or echo's) in
662 the /dev/cpuset virtual file system.
663 4) Start a task that will be the "founding father" of the new job.
664 5) Attach that task to the new cpuset by writing its pid to the
665 /dev/cpuset tasks file for that cpuset.
666 6) fork, exec or clone the job tasks from this founding father task.
667
668For example, the following sequence of commands will setup a cpuset
669named "Charlie", containing just CPUs 2 and 3, and Memory Node 1,
670and then start a subshell 'sh' in that cpuset:
671
672 mount -t cgroup -ocpuset cpuset /dev/cpuset
673 cd /dev/cpuset
674 mkdir Charlie
675 cd Charlie
676 /bin/echo 2-3 > cpus
677 /bin/echo 1 > mems
678 /bin/echo $$ > tasks
679 sh
680 # The subshell 'sh' is now running in cpuset Charlie
681 # The next line should display '/Charlie'
682 cat /proc/self/cpuset
683
684In the future, a C library interface to cpusets will likely be
685available. For now, the only way to query or modify cpusets is
686via the cpuset file system, using the various cd, mkdir, echo, cat,
687rmdir commands from the shell, or their equivalent from C.
688
689The sched_setaffinity calls can also be done at the shell prompt using
690SGI's runon or Robert Love's taskset. The mbind and set_mempolicy
691calls can be done at the shell prompt using the numactl command
692(part of Andi Kleen's numa package).
693
6942. Usage Examples and Syntax
695============================
696
6972.1 Basic Usage
698---------------
699
700Creating, modifying, using the cpusets can be done through the cpuset
701virtual filesystem.
702
703To mount it, type:
704# mount -t cgroup -o cpuset cpuset /dev/cpuset
705
706Then under /dev/cpuset you can find a tree that corresponds to the
707tree of the cpusets in the system. For instance, /dev/cpuset
708is the cpuset that holds the whole system.
709
710If you want to create a new cpuset under /dev/cpuset:
711# cd /dev/cpuset
712# mkdir my_cpuset
713
714Now you want to do something with this cpuset.
715# cd my_cpuset
716
717In this directory you can find several files:
718# ls
719cpu_exclusive memory_migrate mems tasks
720cpus memory_pressure notify_on_release
721mem_exclusive memory_spread_page sched_load_balance
722mem_hardwall memory_spread_slab sched_relax_domain_level
723
724Reading them will give you information about the state of this cpuset:
725the CPUs and Memory Nodes it can use, the processes that are using
726it, its properties. By writing to these files you can manipulate
727the cpuset.
728
729Set some flags:
730# /bin/echo 1 > cpu_exclusive
731
732Add some cpus:
733# /bin/echo 0-7 > cpus
734
735Add some mems:
736# /bin/echo 0-7 > mems
737
738Now attach your shell to this cpuset:
739# /bin/echo $$ > tasks
740
741You can also create cpusets inside your cpuset by using mkdir in this
742directory.
743# mkdir my_sub_cs
744
745To remove a cpuset, just use rmdir:
746# rmdir my_sub_cs
747This will fail if the cpuset is in use (has cpusets inside, or has
748processes attached).
749
750Note that for legacy reasons, the "cpuset" filesystem exists as a
751wrapper around the cgroup filesystem.
752
753The command
754
755mount -t cpuset X /dev/cpuset
756
757is equivalent to
758
759mount -t cgroup -ocpuset X /dev/cpuset
760echo "/sbin/cpuset_release_agent" > /dev/cpuset/release_agent
761
7622.2 Adding/removing cpus
763------------------------
764
765This is the syntax to use when writing in the cpus or mems files
766in cpuset directories:
767
768# /bin/echo 1-4 > cpus -> set cpus list to cpus 1,2,3,4
769# /bin/echo 1,2,3,4 > cpus -> set cpus list to cpus 1,2,3,4
770
7712.3 Setting flags
772-----------------
773
774The syntax is very simple:
775
776# /bin/echo 1 > cpu_exclusive -> set flag 'cpu_exclusive'
777# /bin/echo 0 > cpu_exclusive -> unset flag 'cpu_exclusive'
778
7792.4 Attaching processes
780-----------------------
781
782# /bin/echo PID > tasks
783
784Note that it is PID, not PIDs. You can only attach ONE task at a time.
785If you have several tasks to attach, you have to do it one after another:
786
787# /bin/echo PID1 > tasks
788# /bin/echo PID2 > tasks
789 ...
790# /bin/echo PIDn > tasks
791
792
7933. Questions
794============
795
796Q: what's up with this '/bin/echo' ?
797A: bash's builtin 'echo' command does not check calls to write() against
798 errors. If you use it in the cpuset file system, you won't be
799 able to tell whether a command succeeded or failed.
800
801Q: When I attach processes, only the first of the line gets really attached !
802A: We can only return one error code per call to write(). So you should also
803 put only ONE pid.
804
8054. Contact
806==========
807
808Web: http://www.bullopensource.org/cpuset
diff --git a/Documentation/cgroups/devices.txt b/Documentation/cgroups/devices.txt
new file mode 100644
index 000000000000..7cc6e6a60672
--- /dev/null
+++ b/Documentation/cgroups/devices.txt
@@ -0,0 +1,52 @@
1Device Whitelist Controller
2
31. Description:
4
5Implement a cgroup to track and enforce open and mknod restrictions
6on device files. A device cgroup associates a device access
7whitelist with each cgroup. A whitelist entry has 4 fields.
8'type' is a (all), c (char), or b (block). 'all' means it applies
9to all types and all major and minor numbers. Major and minor are
10either an integer or * for all. Access is a composition of r
11(read), w (write), and m (mknod).
12
13The root device cgroup starts with rwm to 'all'. A child device
14cgroup gets a copy of the parent. Administrators can then remove
15devices from the whitelist or add new entries. A child cgroup can
16never receive a device access which is denied by its parent. However
17when a device access is removed from a parent it will not also be
18removed from the child(ren).
19
202. User Interface
21
22An entry is added using devices.allow, and removed using
23devices.deny. For instance
24
25 echo 'c 1:3 mr' > /cgroups/1/devices.allow
26
27allows cgroup 1 to read and mknod the device usually known as
28/dev/null. Doing
29
30 echo a > /cgroups/1/devices.deny
31
32will remove the default 'a *:* rwm' entry. Doing
33
34 echo a > /cgroups/1/devices.allow
35
36will add the 'a *:* rwm' entry to the whitelist.
37
383. Security
39
40Any task can move itself between cgroups. This clearly won't
41suffice, but we can decide the best way to adequately restrict
42movement as people get some experience with this. We may just want
43to require CAP_SYS_ADMIN, which at least is a separate bit from
44CAP_MKNOD. We may want to just refuse moving to a cgroup which
45isn't a descendent of the current one. Or we may want to use
46CAP_MAC_ADMIN, since we really are trying to lock down root.
47
48CAP_SYS_ADMIN is needed to modify the whitelist or move another
49task to a new cgroup. (Again we'll probably want to change that).
50
51A cgroup may not be granted more permissions than the cgroup's
52parent has.
diff --git a/Documentation/cgroups/memcg_test.txt b/Documentation/cgroups/memcg_test.txt
new file mode 100644
index 000000000000..19533f93b7a2
--- /dev/null
+++ b/Documentation/cgroups/memcg_test.txt
@@ -0,0 +1,342 @@
1Memory Resource Controller(Memcg) Implementation Memo.
2Last Updated: 2008/12/15
3Base Kernel Version: based on 2.6.28-rc8-mm.
4
5Because VM is getting complex (one of reasons is memcg...), memcg's behavior
6is complex. This is a document for memcg's internal behavior.
7Please note that implementation details can be changed.
8
9(*) Topics on API should be in Documentation/cgroups/memory.txt)
10
110. How to record usage ?
12 2 objects are used.
13
14 page_cgroup ....an object per page.
15 Allocated at boot or memory hotplug. Freed at memory hot removal.
16
17 swap_cgroup ... an entry per swp_entry.
18 Allocated at swapon(). Freed at swapoff().
19
20 The page_cgroup has USED bit and double count against a page_cgroup never
21 occurs. swap_cgroup is used only when a charged page is swapped-out.
22
231. Charge
24
25 a page/swp_entry may be charged (usage += PAGE_SIZE) at
26
27 mem_cgroup_newpage_charge()
28 Called at new page fault and Copy-On-Write.
29
30 mem_cgroup_try_charge_swapin()
31 Called at do_swap_page() (page fault on swap entry) and swapoff.
32 Followed by charge-commit-cancel protocol. (With swap accounting)
33 At commit, a charge recorded in swap_cgroup is removed.
34
35 mem_cgroup_cache_charge()
36 Called at add_to_page_cache()
37
38 mem_cgroup_cache_charge_swapin()
39 Called at shmem's swapin.
40
41 mem_cgroup_prepare_migration()
42 Called before migration. "extra" charge is done and followed by
43 charge-commit-cancel protocol.
44 At commit, charge against oldpage or newpage will be committed.
45
462. Uncharge
47 a page/swp_entry may be uncharged (usage -= PAGE_SIZE) by
48
49 mem_cgroup_uncharge_page()
50 Called when an anonymous page is fully unmapped. I.e., mapcount goes
51 to 0. If the page is SwapCache, uncharge is delayed until
52 mem_cgroup_uncharge_swapcache().
53
54 mem_cgroup_uncharge_cache_page()
55 Called when a page-cache is deleted from radix-tree. If the page is
56 SwapCache, uncharge is delayed until mem_cgroup_uncharge_swapcache().
57
58 mem_cgroup_uncharge_swapcache()
59 Called when SwapCache is removed from radix-tree. The charge itself
60 is moved to swap_cgroup. (If mem+swap controller is disabled, no
61 charge to swap occurs.)
62
63 mem_cgroup_uncharge_swap()
64 Called when swp_entry's refcnt goes down to 0. A charge against swap
65 disappears.
66
67 mem_cgroup_end_migration(old, new)
68 At success of migration old is uncharged (if necessary), a charge
69 to new page is committed. At failure, charge to old page is committed.
70
713. charge-commit-cancel
72 In some case, we can't know this "charge" is valid or not at charging
73 (because of races).
74 To handle such case, there are charge-commit-cancel functions.
75 mem_cgroup_try_charge_XXX
76 mem_cgroup_commit_charge_XXX
77 mem_cgroup_cancel_charge_XXX
78 these are used in swap-in and migration.
79
80 At try_charge(), there are no flags to say "this page is charged".
81 at this point, usage += PAGE_SIZE.
82
83 At commit(), the function checks the page should be charged or not
84 and set flags or avoid charging.(usage -= PAGE_SIZE)
85
86 At cancel(), simply usage -= PAGE_SIZE.
87
88Under below explanation, we assume CONFIG_MEM_RES_CTRL_SWAP=y.
89
904. Anonymous
91 Anonymous page is newly allocated at
92 - page fault into MAP_ANONYMOUS mapping.
93 - Copy-On-Write.
94 It is charged right after it's allocated before doing any page table
95 related operations. Of course, it's uncharged when another page is used
96 for the fault address.
97
98 At freeing anonymous page (by exit() or munmap()), zap_pte() is called
99 and pages for ptes are freed one by one.(see mm/memory.c). Uncharges
100 are done at page_remove_rmap() when page_mapcount() goes down to 0.
101
102 Another page freeing is by page-reclaim (vmscan.c) and anonymous
103 pages are swapped out. In this case, the page is marked as
104 PageSwapCache(). uncharge() routine doesn't uncharge the page marked
105 as SwapCache(). It's delayed until __delete_from_swap_cache().
106
107 4.1 Swap-in.
108 At swap-in, the page is taken from swap-cache. There are 2 cases.
109
110 (a) If the SwapCache is newly allocated and read, it has no charges.
111 (b) If the SwapCache has been mapped by processes, it has been
112 charged already.
113
114 This swap-in is one of the most complicated work. In do_swap_page(),
115 following events occur when pte is unchanged.
116
117 (1) the page (SwapCache) is looked up.
118 (2) lock_page()
119 (3) try_charge_swapin()
120 (4) reuse_swap_page() (may call delete_swap_cache())
121 (5) commit_charge_swapin()
122 (6) swap_free().
123
124 Considering following situation for example.
125
126 (A) The page has not been charged before (2) and reuse_swap_page()
127 doesn't call delete_from_swap_cache().
128 (B) The page has not been charged before (2) and reuse_swap_page()
129 calls delete_from_swap_cache().
130 (C) The page has been charged before (2) and reuse_swap_page() doesn't
131 call delete_from_swap_cache().
132 (D) The page has been charged before (2) and reuse_swap_page() calls
133 delete_from_swap_cache().
134
135 memory.usage/memsw.usage changes to this page/swp_entry will be
136 Case (A) (B) (C) (D)
137 Event
138 Before (2) 0/ 1 0/ 1 1/ 1 1/ 1
139 ===========================================
140 (3) +1/+1 +1/+1 +1/+1 +1/+1
141 (4) - 0/ 0 - -1/ 0
142 (5) 0/-1 0/ 0 -1/-1 0/ 0
143 (6) - 0/-1 - 0/-1
144 ===========================================
145 Result 1/ 1 1/ 1 1/ 1 1/ 1
146
147 In any cases, charges to this page should be 1/ 1.
148
149 4.2 Swap-out.
150 At swap-out, typical state transition is below.
151
152 (a) add to swap cache. (marked as SwapCache)
153 swp_entry's refcnt += 1.
154 (b) fully unmapped.
155 swp_entry's refcnt += # of ptes.
156 (c) write back to swap.
157 (d) delete from swap cache. (remove from SwapCache)
158 swp_entry's refcnt -= 1.
159
160
161 At (b), the page is marked as SwapCache and not uncharged.
162 At (d), the page is removed from SwapCache and a charge in page_cgroup
163 is moved to swap_cgroup.
164
165 Finally, at task exit,
166 (e) zap_pte() is called and swp_entry's refcnt -=1 -> 0.
167 Here, a charge in swap_cgroup disappears.
168
1695. Page Cache
170 Page Cache is charged at
171 - add_to_page_cache_locked().
172
173 uncharged at
174 - __remove_from_page_cache().
175
176 The logic is very clear. (About migration, see below)
177 Note: __remove_from_page_cache() is called by remove_from_page_cache()
178 and __remove_mapping().
179
1806. Shmem(tmpfs) Page Cache
181 Memcg's charge/uncharge have special handlers of shmem. The best way
182 to understand shmem's page state transition is to read mm/shmem.c.
183 But brief explanation of the behavior of memcg around shmem will be
184 helpful to understand the logic.
185
186 Shmem's page (just leaf page, not direct/indirect block) can be on
187 - radix-tree of shmem's inode.
188 - SwapCache.
189 - Both on radix-tree and SwapCache. This happens at swap-in
190 and swap-out,
191
192 It's charged when...
193 - A new page is added to shmem's radix-tree.
194 - A swp page is read. (move a charge from swap_cgroup to page_cgroup)
195 It's uncharged when
196 - A page is removed from radix-tree and not SwapCache.
197 - When SwapCache is removed, a charge is moved to swap_cgroup.
198 - When swp_entry's refcnt goes down to 0, a charge in swap_cgroup
199 disappears.
200
2017. Page Migration
202 One of the most complicated functions is page-migration-handler.
203 Memcg has 2 routines. Assume that we are migrating a page's contents
204 from OLDPAGE to NEWPAGE.
205
206 Usual migration logic is..
207 (a) remove the page from LRU.
208 (b) allocate NEWPAGE (migration target)
209 (c) lock by lock_page().
210 (d) unmap all mappings.
211 (e-1) If necessary, replace entry in radix-tree.
212 (e-2) move contents of a page.
213 (f) map all mappings again.
214 (g) pushback the page to LRU.
215 (-) OLDPAGE will be freed.
216
217 Before (g), memcg should complete all necessary charge/uncharge to
218 NEWPAGE/OLDPAGE.
219
220 The point is....
221 - If OLDPAGE is anonymous, all charges will be dropped at (d) because
222 try_to_unmap() drops all mapcount and the page will not be
223 SwapCache.
224
225 - If OLDPAGE is SwapCache, charges will be kept at (g) because
226 __delete_from_swap_cache() isn't called at (e-1)
227
228 - If OLDPAGE is page-cache, charges will be kept at (g) because
229 remove_from_swap_cache() isn't called at (e-1)
230
231 memcg provides following hooks.
232
233 - mem_cgroup_prepare_migration(OLDPAGE)
234 Called after (b) to account a charge (usage += PAGE_SIZE) against
235 memcg which OLDPAGE belongs to.
236
237 - mem_cgroup_end_migration(OLDPAGE, NEWPAGE)
238 Called after (f) before (g).
239 If OLDPAGE is used, commit OLDPAGE again. If OLDPAGE is already
240 charged, a charge by prepare_migration() is automatically canceled.
241 If NEWPAGE is used, commit NEWPAGE and uncharge OLDPAGE.
242
243 But zap_pte() (by exit or munmap) can be called while migration,
244 we have to check if OLDPAGE/NEWPAGE is a valid page after commit().
245
2468. LRU
247 Each memcg has its own private LRU. Now, it's handling is under global
248 VM's control (means that it's handled under global zone->lru_lock).
249 Almost all routines around memcg's LRU is called by global LRU's
250 list management functions under zone->lru_lock().
251
252 A special function is mem_cgroup_isolate_pages(). This scans
253 memcg's private LRU and call __isolate_lru_page() to extract a page
254 from LRU.
255 (By __isolate_lru_page(), the page is removed from both of global and
256 private LRU.)
257
258
2599. Typical Tests.
260
261 Tests for racy cases.
262
263 9.1 Small limit to memcg.
264 When you do test to do racy case, it's good test to set memcg's limit
265 to be very small rather than GB. Many races found in the test under
266 xKB or xxMB limits.
267 (Memory behavior under GB and Memory behavior under MB shows very
268 different situation.)
269
270 9.2 Shmem
271 Historically, memcg's shmem handling was poor and we saw some amount
272 of troubles here. This is because shmem is page-cache but can be
273 SwapCache. Test with shmem/tmpfs is always good test.
274
275 9.3 Migration
276 For NUMA, migration is an another special case. To do easy test, cpuset
277 is useful. Following is a sample script to do migration.
278
279 mount -t cgroup -o cpuset none /opt/cpuset
280
281 mkdir /opt/cpuset/01
282 echo 1 > /opt/cpuset/01/cpuset.cpus
283 echo 0 > /opt/cpuset/01/cpuset.mems
284 echo 1 > /opt/cpuset/01/cpuset.memory_migrate
285 mkdir /opt/cpuset/02
286 echo 1 > /opt/cpuset/02/cpuset.cpus
287 echo 1 > /opt/cpuset/02/cpuset.mems
288 echo 1 > /opt/cpuset/02/cpuset.memory_migrate
289
290 In above set, when you moves a task from 01 to 02, page migration to
291 node 0 to node 1 will occur. Following is a script to migrate all
292 under cpuset.
293 --
294 move_task()
295 {
296 for pid in $1
297 do
298 /bin/echo $pid >$2/tasks 2>/dev/null
299 echo -n $pid
300 echo -n " "
301 done
302 echo END
303 }
304
305 G1_TASK=`cat ${G1}/tasks`
306 G2_TASK=`cat ${G2}/tasks`
307 move_task "${G1_TASK}" ${G2} &
308 --
309 9.4 Memory hotplug.
310 memory hotplug test is one of good test.
311 to offline memory, do following.
312 # echo offline > /sys/devices/system/memory/memoryXXX/state
313 (XXX is the place of memory)
314 This is an easy way to test page migration, too.
315
316 9.5 mkdir/rmdir
317 When using hierarchy, mkdir/rmdir test should be done.
318 Use tests like the following.
319
320 echo 1 >/opt/cgroup/01/memory/use_hierarchy
321 mkdir /opt/cgroup/01/child_a
322 mkdir /opt/cgroup/01/child_b
323
324 set limit to 01.
325 add limit to 01/child_b
326 run jobs under child_a and child_b
327
328 create/delete following groups at random while jobs are running.
329 /opt/cgroup/01/child_a/child_aa
330 /opt/cgroup/01/child_b/child_bb
331 /opt/cgroup/01/child_c
332
333 running new jobs in new group is also good.
334
335 9.6 Mount with other subsystems.
336 Mounting with other subsystems is a good test because there is a
337 race and lock dependency with other cgroup subsystems.
338
339 example)
340 # mount -t cgroup none /cgroup -t cpuset,memory,cpu,devices
341
342 and do task move, mkdir, rmdir etc...under this.
diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
new file mode 100644
index 000000000000..e1501964df1e
--- /dev/null
+++ b/Documentation/cgroups/memory.txt
@@ -0,0 +1,399 @@
1Memory Resource Controller
2
3NOTE: The Memory Resource Controller has been generically been referred
4to as the memory controller in this document. Do not confuse memory controller
5used here with the memory controller that is used in hardware.
6
7Salient features
8
9a. Enable control of both RSS (mapped) and Page Cache (unmapped) pages
10b. The infrastructure allows easy addition of other types of memory to control
11c. Provides *zero overhead* for non memory controller users
12d. Provides a double LRU: global memory pressure causes reclaim from the
13 global LRU; a cgroup on hitting a limit, reclaims from the per
14 cgroup LRU
15
16NOTE: Swap Cache (unmapped) is not accounted now.
17
18Benefits and Purpose of the memory controller
19
20The memory controller isolates the memory behaviour of a group of tasks
21from the rest of the system. The article on LWN [12] mentions some probable
22uses of the memory controller. The memory controller can be used to
23
24a. Isolate an application or a group of applications
25 Memory hungry applications can be isolated and limited to a smaller
26 amount of memory.
27b. Create a cgroup with limited amount of memory, this can be used
28 as a good alternative to booting with mem=XXXX.
29c. Virtualization solutions can control the amount of memory they want
30 to assign to a virtual machine instance.
31d. A CD/DVD burner could control the amount of memory used by the
32 rest of the system to ensure that burning does not fail due to lack
33 of available memory.
34e. There are several other use cases, find one or use the controller just
35 for fun (to learn and hack on the VM subsystem).
36
371. History
38
39The memory controller has a long history. A request for comments for the memory
40controller was posted by Balbir Singh [1]. At the time the RFC was posted
41there were several implementations for memory control. The goal of the
42RFC was to build consensus and agreement for the minimal features required
43for memory control. The first RSS controller was posted by Balbir Singh[2]
44in Feb 2007. Pavel Emelianov [3][4][5] has since posted three versions of the
45RSS controller. At OLS, at the resource management BoF, everyone suggested
46that we handle both page cache and RSS together. Another request was raised
47to allow user space handling of OOM. The current memory controller is
48at version 6; it combines both mapped (RSS) and unmapped Page
49Cache Control [11].
50
512. Memory Control
52
53Memory is a unique resource in the sense that it is present in a limited
54amount. If a task requires a lot of CPU processing, the task can spread
55its processing over a period of hours, days, months or years, but with
56memory, the same physical memory needs to be reused to accomplish the task.
57
58The memory controller implementation has been divided into phases. These
59are:
60
611. Memory controller
622. mlock(2) controller
633. Kernel user memory accounting and slab control
644. user mappings length controller
65
66The memory controller is the first controller developed.
67
682.1. Design
69
70The core of the design is a counter called the res_counter. The res_counter
71tracks the current memory usage and limit of the group of processes associated
72with the controller. Each cgroup has a memory controller specific data
73structure (mem_cgroup) associated with it.
74
752.2. Accounting
76
77 +--------------------+
78 | mem_cgroup |
79 | (res_counter) |
80 +--------------------+
81 / ^ \
82 / | \
83 +---------------+ | +---------------+
84 | mm_struct | |.... | mm_struct |
85 | | | | |
86 +---------------+ | +---------------+
87 |
88 + --------------+
89 |
90 +---------------+ +------+--------+
91 | page +----------> page_cgroup|
92 | | | |
93 +---------------+ +---------------+
94
95 (Figure 1: Hierarchy of Accounting)
96
97
98Figure 1 shows the important aspects of the controller
99
1001. Accounting happens per cgroup
1012. Each mm_struct knows about which cgroup it belongs to
1023. Each page has a pointer to the page_cgroup, which in turn knows the
103 cgroup it belongs to
104
105The accounting is done as follows: mem_cgroup_charge() is invoked to setup
106the necessary data structures and check if the cgroup that is being charged
107is over its limit. If it is then reclaim is invoked on the cgroup.
108More details can be found in the reclaim section of this document.
109If everything goes well, a page meta-data-structure called page_cgroup is
110allocated and associated with the page. This routine also adds the page to
111the per cgroup LRU.
112
1132.2.1 Accounting details
114
115All mapped anon pages (RSS) and cache pages (Page Cache) are accounted.
116(some pages which never be reclaimable and will not be on global LRU
117 are not accounted. we just accounts pages under usual vm management.)
118
119RSS pages are accounted at page_fault unless they've already been accounted
120for earlier. A file page will be accounted for as Page Cache when it's
121inserted into inode (radix-tree). While it's mapped into the page tables of
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.
131
1322.3 Shared Page Accounting
133
134Shared pages are accounted on the basis of the first touch approach. The
135cgroup that first touches a page is accounted for the page. The principle
136behind this approach is that a cgroup that aggressively uses a shared
137page will eventually get charged for it (once it is uncharged from
138the cgroup that brought it in -- this will happen on memory pressure).
139
140Exception: If CONFIG_CGROUP_CGROUP_MEM_RES_CTLR_SWAP is not used..
141When you do swapoff and make swapped-out pages of shmem(tmpfs) to
142be backed into memory in force, charges for pages are accounted against the
143caller of swapoff rather than the users of shmem.
144
145
1462.4 Swap Extension (CONFIG_CGROUP_MEM_RES_CTLR_SWAP)
147Swap Extension allows you to record charge for swap. A swapped-in page is
148charged back to original page allocator if possible.
149
150When swap is accounted, following files are added.
151 - memory.memsw.usage_in_bytes.
152 - memory.memsw.limit_in_bytes.
153
154usage of mem+swap is limited by memsw.limit_in_bytes.
155
156Note: why 'mem+swap' rather than swap.
157The global LRU(kswapd) can swap out arbitrary pages. Swap-out means
158to move account from memory to swap...there is no change in usage of
159mem+swap.
160
161In other words, when we want to limit the usage of swap without affecting
162global LRU, mem+swap limit is better than just limiting swap from OS point
163of view.
164
1652.5 Reclaim
166
167Each cgroup maintains a per cgroup LRU that consists of an active
168and inactive list. When a cgroup goes over its limit, we first try
169to reclaim memory from the cgroup so as to make space for the new
170pages that the cgroup has touched. If the reclaim is unsuccessful,
171an OOM routine is invoked to select and kill the bulkiest task in the
172cgroup.
173
174The reclaim algorithm has not been modified for cgroups, except that
175pages that are selected for reclaiming come from the per cgroup LRU
176list.
177
1782. Locking
179
180The memory controller uses the following hierarchy
181
1821. zone->lru_lock is used for selecting pages to be isolated
1832. mem->per_zone->lru_lock protects the per cgroup LRU (per zone)
1843. lock_page_cgroup() is used to protect page->page_cgroup
185
1863. User Interface
187
1880. Configuration
189
190a. Enable CONFIG_CGROUPS
191b. Enable CONFIG_RESOURCE_COUNTERS
192c. Enable CONFIG_CGROUP_MEM_RES_CTLR
193
1941. Prepare the cgroups
195# mkdir -p /cgroups
196# mount -t cgroup none /cgroups -o memory
197
1982. Make the new group and move bash into it
199# mkdir /cgroups/0
200# echo $$ > /cgroups/0/tasks
201
202Since now we're in the 0 cgroup,
203We can alter the memory limit:
204# echo 4M > /cgroups/0/memory.limit_in_bytes
205
206NOTE: We can use a suffix (k, K, m, M, g or G) to indicate values in kilo,
207mega or gigabytes.
208
209# cat /cgroups/0/memory.limit_in_bytes
2104194304
211
212NOTE: The interface has now changed to display the usage in bytes
213instead of pages
214
215We can check the usage:
216# cat /cgroups/0/memory.usage_in_bytes
2171216512
218
219A successful write to this file does not guarantee a successful set of
220this limit to the value written into the file. This can be due to a
221number of factors, such as rounding up to page boundaries or the total
222availability of memory on the system. The user is required to re-read
223this file after a write to guarantee the value committed by the kernel.
224
225# echo 1 > memory.limit_in_bytes
226# cat memory.limit_in_bytes
2274096
228
229The memory.failcnt field gives the number of times that the cgroup limit was
230exceeded.
231
232The memory.stat file gives accounting information. Now, the number of
233caches, RSS and Active pages/Inactive pages are shown.
234
2354. Testing
236
237Balbir posted lmbench, AIM9, LTP and vmmstress results [10] and [11].
238Apart from that v6 has been tested with several applications and regular
239daily use. The controller has also been tested on the PPC64, x86_64 and
240UML platforms.
241
2424.1 Troubleshooting
243
244Sometimes a user might find that the application under a cgroup is
245terminated. There are several causes for this:
246
2471. The cgroup limit is too low (just too low to do anything useful)
2482. The user is using anonymous memory and swap is turned off or too low
249
250A sync followed by echo 1 > /proc/sys/vm/drop_caches will help get rid of
251some of the pages cached in the cgroup (page cache pages).
252
2534.2 Task migration
254
255When a task migrates from one cgroup to another, it's charge is not
256carried forward. The pages allocated from the original cgroup still
257remain charged to it, the charge is dropped when the page is freed or
258reclaimed.
259
2604.3 Removing a cgroup
261
262A cgroup can be removed by rmdir, but as discussed in sections 4.1 and 4.2, a
263cgroup might have some charge associated with it, even though all
264tasks have migrated away from it.
265Such charges are freed(at default) or moved to its parent. When moved,
266both of RSS and CACHES are moved to parent.
267If both of them are busy, rmdir() returns -EBUSY. See 5.1 Also.
268
269Charges recorded in swap information is not updated at removal of cgroup.
270Recorded information is discarded and a cgroup which uses swap (swapcache)
271will be charged as a new owner of it.
272
273
2745. Misc. interfaces.
275
2765.1 force_empty
277 memory.force_empty interface is provided to make cgroup's memory usage empty.
278 You can use this interface only when the cgroup has no tasks.
279 When writing anything to this
280
281 # echo 0 > memory.force_empty
282
283 Almost all pages tracked by this memcg will be unmapped and freed. Some of
284 pages cannot be freed because it's locked or in-use. Such pages are moved
285 to parent and this cgroup will be empty. But this may return -EBUSY in
286 some too busy case.
287
288 Typical use case of this interface is that calling this before rmdir().
289 Because rmdir() moves all pages to parent, some out-of-use page caches can be
290 moved to the parent. If you want to avoid that, force_empty will be useful.
291
2925.2 stat file
293 memory.stat file includes following statistics (now)
294 cache - # of pages from page-cache and shmem.
295 rss - # of pages from anonymous memory.
296 pgpgin - # of event of charging
297 pgpgout - # of event of uncharging
298 active_anon - # of pages on active lru of anon, shmem.
299 inactive_anon - # of pages on active lru of anon, shmem
300 active_file - # of pages on active lru of file-cache
301 inactive_file - # of pages on inactive lru of file cache
302 unevictable - # of pages cannot be reclaimed.(mlocked etc)
303
304 Below is depend on CONFIG_DEBUG_VM.
305 inactive_ratio - VM inernal parameter. (see mm/page_alloc.c)
306 recent_rotated_anon - VM internal parameter. (see mm/vmscan.c)
307 recent_rotated_file - VM internal parameter. (see mm/vmscan.c)
308 recent_scanned_anon - VM internal parameter. (see mm/vmscan.c)
309 recent_scanned_file - VM internal parameter. (see mm/vmscan.c)
310
311 Memo:
312 recent_rotated means recent frequency of lru rotation.
313 recent_scanned means recent # of scans to lru.
314 showing for better debug please see the code for meanings.
315
316
3175.3 swappiness
318 Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only.
319
320 Following cgroup's swapiness can't be changed.
321 - root cgroup (uses /proc/sys/vm/swappiness).
322 - a cgroup which uses hierarchy and it has child cgroup.
323 - a cgroup which uses hierarchy and not the root of hierarchy.
324
325
3266. Hierarchy support
327
328The memory controller supports a deep hierarchy and hierarchical accounting.
329The hierarchy is created by creating the appropriate cgroups in the
330cgroup filesystem. Consider for example, the following cgroup filesystem
331hierarchy
332
333 root
334 / | \
335 / | \
336 a b c
337 | \
338 | \
339 d e
340
341In the diagram above, with hierarchical accounting enabled, all memory
342usage of e, is accounted to its ancestors up until the root (i.e, c and root),
343that has memory.use_hierarchy enabled. If one of the ancestors goes over its
344limit, the reclaim algorithm reclaims from the tasks in the ancestor and the
345children of the ancestor.
346
3476.1 Enabling hierarchical accounting and reclaim
348
349The memory controller by default disables the hierarchy feature. Support
350can be enabled by writing 1 to memory.use_hierarchy file of the root cgroup
351
352# echo 1 > memory.use_hierarchy
353
354The feature can be disabled by
355
356# echo 0 > memory.use_hierarchy
357
358NOTE1: Enabling/disabling will fail if the cgroup already has other
359cgroups created below it.
360
361NOTE2: This feature can be enabled/disabled per subtree.
362
3637. TODO
364
3651. Add support for accounting huge pages (as a separate controller)
3662. Make per-cgroup scanner reclaim not-shared pages first
3673. Teach controller to account for shared-pages
3684. Start reclamation in the background when the limit is
369 not yet hit but the usage is getting closer
370
371Summary
372
373Overall, the memory controller has been a stable controller and has been
374commented and discussed quite extensively in the community.
375
376References
377
3781. Singh, Balbir. RFC: Memory Controller, http://lwn.net/Articles/206697/
3792. Singh, Balbir. Memory Controller (RSS Control),
380 http://lwn.net/Articles/222762/
3813. Emelianov, Pavel. Resource controllers based on process cgroups
382 http://lkml.org/lkml/2007/3/6/198
3834. Emelianov, Pavel. RSS controller based on process cgroups (v2)
384 http://lkml.org/lkml/2007/4/9/78
3855. Emelianov, Pavel. RSS controller based on process cgroups (v3)
386 http://lkml.org/lkml/2007/5/30/244
3876. Menage, Paul. Control Groups v10, http://lwn.net/Articles/236032/
3887. Vaidyanathan, Srinivasan, Control Groups: Pagecache accounting and control
389 subsystem (v3), http://lwn.net/Articles/235534/
3908. Singh, Balbir. RSS controller v2 test results (lmbench),
391 http://lkml.org/lkml/2007/5/17/232
3929. Singh, Balbir. RSS controller v2 AIM9 results
393 http://lkml.org/lkml/2007/5/18/1
39410. Singh, Balbir. Memory controller v6 test results,
395 http://lkml.org/lkml/2007/8/19/36
39611. Singh, Balbir. Memory controller introduction (v6),
397 http://lkml.org/lkml/2007/8/17/69
39812. Corbet, Jonathan, Controlling memory use in cgroups,
399 http://lwn.net/Articles/243795/
diff --git a/Documentation/cgroups/resource_counter.txt b/Documentation/cgroups/resource_counter.txt
new file mode 100644
index 000000000000..f196ac1d7d25
--- /dev/null
+++ b/Documentation/cgroups/resource_counter.txt
@@ -0,0 +1,181 @@
1
2 The Resource Counter
3
4The resource counter, declared at include/linux/res_counter.h,
5is supposed to facilitate the resource management by controllers
6by providing common stuff for accounting.
7
8This "stuff" includes the res_counter structure and routines
9to work with it.
10
11
12
131. Crucial parts of the res_counter structure
14
15 a. unsigned long long usage
16
17 The usage value shows the amount of a resource that is consumed
18 by a group at a given time. The units of measurement should be
19 determined by the controller that uses this counter. E.g. it can
20 be bytes, items or any other unit the controller operates on.
21
22 b. unsigned long long max_usage
23
24 The maximal value of the usage over time.
25
26 This value is useful when gathering statistical information about
27 the particular group, as it shows the actual resource requirements
28 for a particular group, not just some usage snapshot.
29
30 c. unsigned long long limit
31
32 The maximal allowed amount of resource to consume by the group. In
33 case the group requests for more resources, so that the usage value
34 would exceed the limit, the resource allocation is rejected (see
35 the next section).
36
37 d. unsigned long long failcnt
38
39 The failcnt stands for "failures counter". This is the number of
40 resource allocation attempts that failed.
41
42 c. spinlock_t lock
43
44 Protects changes of the above values.
45
46
47
482. Basic accounting routines
49
50 a. void res_counter_init(struct res_counter *rc)
51
52 Initializes the resource counter. As usual, should be the first
53 routine called for a new counter.
54
55 b. int res_counter_charge[_locked]
56 (struct res_counter *rc, unsigned long val)
57
58 When a resource is about to be allocated it has to be accounted
59 with the appropriate resource counter (controller should determine
60 which one to use on its own). This operation is called "charging".
61
62 This is not very important which operation - resource allocation
63 or charging - is performed first, but
64 * if the allocation is performed first, this may create a
65 temporary resource over-usage by the time resource counter is
66 charged;
67 * if the charging is performed first, then it should be uncharged
68 on error path (if the one is called).
69
70 c. void res_counter_uncharge[_locked]
71 (struct res_counter *rc, unsigned long val)
72
73 When a resource is released (freed) it should be de-accounted
74 from the resource counter it was accounted to. This is called
75 "uncharging".
76
77 The _locked routines imply that the res_counter->lock is taken.
78
79
80 2.1 Other accounting routines
81
82 There are more routines that may help you with common needs, like
83 checking whether the limit is reached or resetting the max_usage
84 value. They are all declared in include/linux/res_counter.h.
85
86
87
883. Analyzing the resource counter registrations
89
90 a. If the failcnt value constantly grows, this means that the counter's
91 limit is too tight. Either the group is misbehaving and consumes too
92 many resources, or the configuration is not suitable for the group
93 and the limit should be increased.
94
95 b. The max_usage value can be used to quickly tune the group. One may
96 set the limits to maximal values and either load the container with
97 a common pattern or leave one for a while. After this the max_usage
98 value shows the amount of memory the container would require during
99 its common activity.
100
101 Setting the limit a bit above this value gives a pretty good
102 configuration that works in most of the cases.
103
104 c. If the max_usage is much less than the limit, but the failcnt value
105 is growing, then the group tries to allocate a big chunk of resource
106 at once.
107
108 d. If the max_usage is much less than the limit, but the failcnt value
109 is 0, then this group is given too high limit, that it does not
110 require. It is better to lower the limit a bit leaving more resource
111 for other groups.
112
113
114
1154. Communication with the control groups subsystem (cgroups)
116
117All the resource controllers that are using cgroups and resource counters
118should provide files (in the cgroup filesystem) to work with the resource
119counter fields. They are recommended to adhere to the following rules:
120
121 a. File names
122
123 Field name File name
124 ---------------------------------------------------
125 usage usage_in_<unit_of_measurement>
126 max_usage max_usage_in_<unit_of_measurement>
127 limit limit_in_<unit_of_measurement>
128 failcnt failcnt
129 lock no file :)
130
131 b. Reading from file should show the corresponding field value in the
132 appropriate format.
133
134 c. Writing to file
135
136 Field Expected behavior
137 ----------------------------------
138 usage prohibited
139 max_usage reset to usage
140 limit set the limit
141 failcnt reset to zero
142
143
144
1455. Usage example
146
147 a. Declare a task group (take a look at cgroups subsystem for this) and
148 fold a res_counter into it
149
150 struct my_group {
151 struct res_counter res;
152
153 <other fields>
154 }
155
156 b. Put hooks in resource allocation/release paths
157
158 int alloc_something(...)
159 {
160 if (res_counter_charge(res_counter_ptr, amount) < 0)
161 return -ENOMEM;
162
163 <allocate the resource and return to the caller>
164 }
165
166 void release_something(...)
167 {
168 res_counter_uncharge(res_counter_ptr, amount);
169
170 <release the resource>
171 }
172
173 In order to keep the usage value self-consistent, both the
174 "res_counter_ptr" and the "amount" in release_something() should be
175 the same as they were in the alloc_something() when the releasing
176 resource was allocated.
177
178 c. Provide the way to read res_counter values and set them (the cgroups
179 still can help with it).
180
181 c. Compile and run :)