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memcg: update documentation to describe usage_in_bytes

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Since 569b846d ("memcg: coalesce uncharge during unmap/truncate"), we do
batched (delayed) uncharge at truncation/unmap.  And since cdec2e42(memcg:
coalesce charging via percpu storage), we have percpu cache for
res_counter.

These changes improved performance of memory cgroup very much, but made
res_counter->usage usually have a bigger value than the actual value of
memory usage.  So, *.usage_in_bytes, which show res_counter->usage, are
not desirable for precise values of memory(and swap) usage anymore.

Instead of removing these files completely(because we cannot know
res_counter->usage without them), this patch updates the meaning of those
files.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Daisuke Nishimura 2011-04-27 15:26:48 -07:00 committed by Linus Torvalds
parent 98909cf0d1
commit a111c966a6
1 changed files with 13 additions and 2 deletions
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15
Documentation/cgroups/memory.txt
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@ -52,8 +52,10 @@ Brief summary of control files.
tasks # attach a task(thread) and show list of threads
cgroup.procs # show list of processes
cgroup.event_control # an interface for event_fd()
memory.usage_in_bytes # show current memory(RSS+Cache) usage.
memory.memsw.usage_in_bytes # show current memory+Swap usage
memory.usage_in_bytes # show current res_counter usage for memory
(See 5.5 for details)
memory.memsw.usage_in_bytes # show current res_counter usage for memory+Swap
(See 5.5 for details)
memory.limit_in_bytes # set/show limit of memory usage
memory.memsw.limit_in_bytes # set/show limit of memory+Swap usage
memory.failcnt # show the number of memory usage hits limits
@ -453,6 +455,15 @@ memory under it will be reclaimed.
You can reset failcnt by writing 0 to failcnt file.
# echo 0 > .../memory.failcnt
5.5 usage_in_bytes
For efficiency, as other kernel components, memory cgroup uses some optimization
to avoid unnecessary cacheline false sharing. usage_in_bytes is affected by the
method and doesn't show 'exact' value of memory(and swap) usage, it's an fuzz
value for efficient access. (Of course, when necessary, it's synchronized.)
If you want to know more exact memory usage, you should use RSS+CACHE(+SWAP)
value in memory.stat(see 5.2).
6. Hierarchy support
The memory controller supports a deep hierarchy and hierarchical accounting.