memcg: fix behavior of mem_cgroup_resize_limit()

Commit 22a668d7c3ef ("memcg: fix behavior under memory.limit equals to
memsw.limit") introduced "memsw_is_minimum" flag, which becomes true
when mem_limit == memsw_limit.  The flag is checked at the beginning of
reclaim, and "noswap" is set if the flag is true, because using swap is
meaningless in this case.

This works well in most cases, but when we try to shrink mem_limit,
which is the same as memsw_limit now, we might fail to shrink mem_limit
because swap doesn't used.

This patch fixes this behavior by:
 - check MEM_CGROUP_RECLAIM_SHRINK at the begining of reclaim
 - If it is set, don't set "noswap" flag even if memsw_is_minimum is true.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <bsingharora@gmail.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Ying Han <yinghan@google.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c0b065ec1571990fd90efe1af42d1a65457f68cb..dfeca594fd7a22e54548ed2269f7383f7a3eaf9f 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1653,7 +1653,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
        excess = res_counter_soft_limit_excess(&root_mem->res) >> PAGE_SHIFT;
 
        /* If memsw_is_minimum==1, swap-out is of-no-use. */
-       if (!check_soft && root_mem->memsw_is_minimum)
+       if (!check_soft && !shrink && root_mem->memsw_is_minimum)
                noswap = true;
 
        while (1) {