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Subject[PATCH v4 25/25] Documentation: add documentation for slab tracker for memcg
In a separate patch, to aid reviewers.

Signed-off-by: Glauber Costa <>
CC: Christoph Lameter <>
CC: Pekka Enberg <>
CC: Michal Hocko <>
CC: Kamezawa Hiroyuki <>
CC: Johannes Weiner <>
CC: Suleiman Souhlal <>
CC: Randy Dunlap <>
Documentation/cgroups/memory.txt | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)

diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index 9b1067a..9ea82b5 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -74,6 +74,12 @@ Brief summary of control files.
memory.kmem.tcp.limit_in_bytes # set/show hard limit for tcp buf memory
memory.kmem.tcp.usage_in_bytes # show current tcp buf memory allocation

+ memory.kmem.limit_in_bytes # set/show hard limit for general kmem memory
+ memory.kmem.usage_in_bytes # show current general kmem memory allocation
+ memory.kmem.failcnt # show current number of kmem limit hits
+ memory.kmem.max_usage_in_bytes # show max kmem usage
+ memory.kmem.slabinfo # show cgroup-specific slab usage information
1. History

The memory controller has a long history. A request for comments for the memory
@@ -270,6 +276,14 @@ cgroup may or may not be accounted.
Currently no soft limit is implemented for kernel memory. It is future work
to trigger slab reclaim when those limits are reached.

+Kernel memory is not accounted until it is limited. Users that want to just
+track kernel memory usage can set the limit value to a big enough value so
+the limit is guaranteed to never hit. A kernel memory limit bigger than the
+current memory limit will have this effect as well.
+This guarantes that this extension is backwards compatible to any previous
+memory cgroup version.
2.7.1 Current Kernel Memory resources accounted

* sockets memory pressure: some sockets protocols have memory pressure
@@ -278,6 +292,24 @@ per cgroup, instead of globally.

* tcp memory pressure: sockets memory pressure for the tcp protocol.

+* slab/kmalloc:
+When slab memory is tracked (memory.kmem.limit_in_bytes != -1ULL), both
+memory.kmem.usage_in_bytes and memory.usage_in_bytes are updated. When
+memory.kmem.limit_in_bytes is left alone, no tracking of slab caches takes
+Because a slab page is shared among many tasks, it is not possible to take
+any meaningful action upon task migration. Slabs created in a cgroup stay
+around until the cgroup is destructed. Information about the slabs used
+by the cgroup is displayed in the cgroup file memory.kmem.slabinfo. The format
+of this file is and should remain compatible with /proc/slabinfo.
+Upon cgroup destruction, slabs that holds no live references are destructed.
+Workers are fired to destroy the remaining caches as they objects are freed.
+Memory used by dead caches are shown in the proc file /proc/dead_slabinfo
3. User Interface

0. Configuration
@@ -286,6 +318,7 @@ a. Enable CONFIG_CGROUPS
d. Enable CONFIG_CGROUP_MEM_RES_CTLR_SWAP (to use swap extension)
+d. Enable CONFIG_CGROUP_MEM_RES_CTLR_KMEM (to use experimental kmem extension)

1. Prepare the cgroups (see cgroups.txt, Why are cgroups needed?)
# mount -t tmpfs none /sys/fs/cgroup

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