From a111c966a65e4b5d9c6fd2d8459978c1407077d5 Mon Sep 17 00:00:00 2001 From: Daisuke Nishimura Date: Wed, 27 Apr 2011 15:26:48 -0700 Subject: [PATCH] memcg: update documentation to describe usage_in_bytes 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 Acked-by: KAMEZAWA Hiroyuki Acked-by: Michal Hocko Cc: Balbir Singh Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/cgroups/memory.txt | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index b6ed61c95856..7c163477fcd8 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -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. -- 2.30.2