3 files changed, 139 insertions, 6 deletions

diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index bcf1a00b06a1..638bf17ff869 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -442,7 +442,7 @@ You can attach the current shell task by echoing 0:
 You can use the cgroup.procs file instead of the tasks file to move all
 threads in a threadgroup at once. Echoing the PID of any task in a
 threadgroup to cgroup.procs causes all tasks in that threadgroup to be
-be attached to the cgroup. Writing 0 to cgroup.procs moves all tasks
+attached to the cgroup. Writing 0 to cgroup.procs moves all tasks
 in the writing task's threadgroup.
 
 Note: Since every task is always a member of exactly one cgroup in each
@@ -580,6 +580,7 @@ propagation along the hierarchy. See the comment on
 cgroup_for_each_descendant_pre() for details.
 
 void css_offline(struct cgroup *cgrp);
+(cgroup_mutex held by caller)
 
 This is the counterpart of css_online() and called iff css_online()
 has succeeded on @cgrp. This signifies the beginning of the end of
diff --git a/Documentation/cgroups/devices.txt b/Documentation/cgroups/devices.txt
index 16624a7f8222..3c1095ca02ea 100644
--- a/Documentation/cgroups/devices.txt
+++ b/Documentation/cgroups/devices.txt
@@ -13,9 +13,7 @@ either an integer or * for all.  Access is a composition of r
 The root device cgroup starts with rwm to 'all'.  A child device
 cgroup gets a copy of the parent.  Administrators can then remove
 devices from the whitelist or add new entries.  A child cgroup can
-never receive a device access which is denied by its parent.  However
-when a device access is removed from a parent it will not also be
-removed from the child(ren).
+never receive a device access which is denied by its parent.
 
 2. User Interface
 
@@ -50,3 +48,69 @@ task to a new cgroup.  (Again we'll probably want to change that).
 
 A cgroup may not be granted more permissions than the cgroup's
 parent has.
+
+4. Hierarchy
+
+device cgroups maintain hierarchy by making sure a cgroup never has more
+access permissions than its parent.  Every time an entry is written to
+a cgroup's devices.deny file, all its children will have that entry removed
+from their whitelist and all the locally set whitelist entries will be
+re-evaluated.  In case one of the locally set whitelist entries would provide
+more access than the cgroup's parent, it'll be removed from the whitelist.
+
+Example:
+      A
+     / \
+        B
+
+    group        behavior       exceptions
+    A            allow          "b 8:* rwm", "c 116:1 rw"
+    B            deny           "c 1:3 rwm", "c 116:2 rwm", "b 3:* rwm"
+
+If a device is denied in group A:
+        # echo "c 116:* r" > A/devices.deny
+it'll propagate down and after revalidating B's entries, the whitelist entry
+"c 116:2 rwm" will be removed:
+
+    group        whitelist entries                        denied devices
+    A            all                                      "b 8:* rwm", "c 116:* rw"
+    B            "c 1:3 rwm", "b 3:* rwm"                 all the rest
+
+In case parent's exceptions change and local exceptions are not allowed
+anymore, they'll be deleted.
+
+Notice that new whitelist entries will not be propagated:
+      A
+     / \
+        B
+
+    group        whitelist entries                        denied devices
+    A            "c 1:3 rwm", "c 1:5 r"                   all the rest
+    B            "c 1:3 rwm", "c 1:5 r"                   all the rest
+
+when adding "c *:3 rwm":
+        # echo "c *:3 rwm" >A/devices.allow
+
+the result:
+    group        whitelist entries                        denied devices
+    A            "c *:3 rwm", "c 1:5 r"                   all the rest
+    B            "c 1:3 rwm", "c 1:5 r"                   all the rest
+
+but now it'll be possible to add new entries to B:
+        # echo "c 2:3 rwm" >B/devices.allow
+        # echo "c 50:3 r" >B/devices.allow
+or even
+        # echo "c *:3 rwm" >B/devices.allow
+
+Allowing or denying all by writing 'a' to devices.allow or devices.deny will
+not be possible once the device cgroups has children.
+
+4.1 Hierarchy (internal implementation)
+
+device cgroups is implemented internally using a behavior (ALLOW, DENY) and a
+list of exceptions.  The internal state is controlled using the same user
+interface to preserve compatibility with the previous whitelist-only
+implementation.  Removal or addition of exceptions that will reduce the access
+to devices will be propagated down the hierarchy.
+For every propagated exception, the effective rules will be re-evaluated based
+on current parent's access rules.
diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index 8b8c28b9864c..09027a9fece5 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -40,6 +40,7 @@ Features:
  - soft limit
  - moving (recharging) account at moving a task is selectable.
  - usage threshold notifier
+ - memory pressure notifier
  - oom-killer disable knob and oom-notifier
  - Root cgroup has no limit controls.
 
@@ -65,6 +66,7 @@ Brief summary of control files.
  memory.stat                     # show various statistics
  memory.use_hierarchy            # set/show hierarchical account enabled
  memory.force_empty              # trigger forced move charge to parent
+ memory.pressure_level           # set memory pressure notifications
  memory.swappiness               # set/show swappiness parameter of vmscan
                                  (See sysctl's vm.swappiness)
  memory.move_charge_at_immigrate # set/show controls of moving charges
@@ -194,7 +196,7 @@ the cgroup that brought it in -- this will happen on memory pressure).
 But see section 8.2: when moving a task to another cgroup, its pages may
 be recharged to the new cgroup, if move_charge_at_immigrate has been chosen.
 
-Exception: If CONFIG_CGROUP_CGROUP_MEMCG_SWAP is not used.
+Exception: If CONFIG_MEMCG_SWAP is not used.
 When you do swapoff and make swapped-out pages of shmem(tmpfs) to
 be backed into memory in force, charges for pages are accounted against the
 caller of swapoff rather than the users of shmem.
@@ -762,7 +764,73 @@ At reading, current status of OOM is shown.
         under_oom        0 or 1 (if 1, the memory cgroup is under OOM, tasks may
                                  be stopped.)
 
-11. TODO
+11. Memory Pressure
+
+The pressure level notifications can be used to monitor the memory
+allocation cost; based on the pressure, applications can implement
+different strategies of managing their memory resources. The pressure
+levels are defined as following:
+
+The "low" level means that the system is reclaiming memory for new
+allocations. Monitoring this reclaiming activity might be useful for
+maintaining cache level. Upon notification, the program (typically
+"Activity Manager") might analyze vmstat and act in advance (i.e.
+prematurely shutdown unimportant services).
+
+The "medium" level means that the system is experiencing medium memory
+pressure, the system might be making swap, paging out active file caches,
+etc. Upon this event applications may decide to further analyze
+vmstat/zoneinfo/memcg or internal memory usage statistics and free any
+resources that can be easily reconstructed or re-read from a disk.
+
+The "critical" level means that the system is actively thrashing, it is
+about to out of memory (OOM) or even the in-kernel OOM killer is on its
+way to trigger. Applications should do whatever they can to help the
+system. It might be too late to consult with vmstat or any other
+statistics, so it's advisable to take an immediate action.
+
+The events are propagated upward until the event is handled, i.e. the
+events are not pass-through. Here is what this means: for example you have
+three cgroups: A->B->C. Now you set up an event listener on cgroups A, B
+and C, and suppose group C experiences some pressure. In this situation,
+only group C will receive the notification, i.e. groups A and B will not
+receive it. This is done to avoid excessive "broadcasting" of messages,
+which disturbs the system and which is especially bad if we are low on
+memory or thrashing. So, organize the cgroups wisely, or propagate the
+events manually (or, ask us to implement the pass-through events,
+explaining why would you need them.)
+
+The file memory.pressure_level is only used to setup an eventfd. To
+register a notification, an application must:
+
+- create an eventfd using eventfd(2);
+- open memory.pressure_level;
+- write string like "<event_fd> <fd of memory.pressure_level> <level>"
+  to cgroup.event_control.
+
+Application will be notified through eventfd when memory pressure is at
+the specific level (or higher). Read/write operations to
+memory.pressure_level are no implemented.
+
+Test:
+
+   Here is a small script example that makes a new cgroup, sets up a
+   memory limit, sets up a notification in the cgroup and then makes child
+   cgroup experience a critical pressure:
+
+   # cd /sys/fs/cgroup/memory/
+   # mkdir foo
+   # cd foo
+   # cgroup_event_listener memory.pressure_level low &
+   # echo 8000000 > memory.limit_in_bytes
+   # echo 8000000 > memory.memsw.limit_in_bytes
+   # echo $$ > tasks
+   # dd if=/dev/zero | read x
+
+   (Expect a bunch of notifications, and eventually, the oom-killer will
+   trigger.)
+
+12. TODO
 
 1. Add support for accounting huge pages (as a separate controller)
 2. Make per-cgroup scanner reclaim not-shared pages first