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memcg: fix behavior under memory.limit equals to memsw.limit

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A user can set memcg.limit_in_bytes == memcg.memsw.limit_in_bytes when the
user just want to limit the total size of applications, in other words,
not very interested in memory usage itself.  In this case, swap-out will
be done only by global-LRU.

But, under current implementation, memory.limit_in_bytes is checked at
first and try_to_free_page() may do swap-out.  But, that swap-out is
useless for memsw.limit_in_bytes and the thread may hit limit again.

This patch tries to fix the current behavior at memory.limit ==
memsw.limit case.  And documentation is updated to explain the behavior of
this special case.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
KAMEZAWA Hiroyuki
2009-06-17 16:27:19 -07:00
committed by Linus Torvalds
parent 8a9478ca7f
commit 22a668d7c3
2 changed files with 29 additions and 5 deletions
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15
Documentation/cgroups/memory.txt
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@@ -152,14 +152,19 @@ When swap is accounted, following files are added.
usage of mem+swap is limited by memsw.limit_in_bytes.
Note: why 'mem+swap' rather than swap.
* why 'mem+swap' rather than swap.
The global LRU(kswapd) can swap out arbitrary pages. Swap-out means
to move account from memory to swap...there is no change in usage of
mem+swap.
mem+swap. In other words, when we want to limit the usage of swap without
affecting global LRU, mem+swap limit is better than just limiting swap from
OS point of view.
In other words, when we want to limit the usage of swap without affecting
global LRU, mem+swap limit is better than just limiting swap from OS point
of view.
* What happens when a cgroup hits memory.memsw.limit_in_bytes
When a cgroup his memory.memsw.limit_in_bytes, it's useless to do swap-out
in this cgroup. Then, swap-out will not be done by cgroup routine and file
caches are dropped. But as mentioned above, global LRU can do swapout memory
from it for sanity of the system's memory management state. You can't forbid
it by cgroup.
2.5 Reclaim