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

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>

1 files changed, 19 insertions, 0 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a83e0395444b..6ceb6f2dbac2 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -177,6 +177,9 @@ struct mem_cgroup {
 
         unsigned int    swappiness;
 
+        /* set when res.limit == memsw.limit */
+        bool            memsw_is_minimum;
+
         /*
          * statistics. This must be placed at the end of memcg.
          */
@@ -847,6 +850,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
         int ret, total = 0;
         int loop = 0;
 
+        /* If memsw_is_minimum==1, swap-out is of-no-use. */
+        if (root_mem->memsw_is_minimum)
+                noswap = true;
+
         while (loop < 2) {
                 victim = mem_cgroup_select_victim(root_mem);
                 if (victim == root_mem)
@@ -1752,6 +1759,12 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
                         break;
                 }
                 ret = res_counter_set_limit(&memcg->res, val);
+                if (!ret) {
+                        if (memswlimit == val)
+                                memcg->memsw_is_minimum = true;
+                        else
+                                memcg->memsw_is_minimum = false;
+                }
                 mutex_unlock(&set_limit_mutex);
 
                 if (!ret)
@@ -1799,6 +1812,12 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
                         break;
                 }
                 ret = res_counter_set_limit(&memcg->memsw, val);
+                if (!ret) {
+                        if (memlimit == val)
+                                memcg->memsw_is_minimum = true;
+                        else
+                                memcg->memsw_is_minimum = false;
+                }
                 mutex_unlock(&set_limit_mutex);
 
                 if (!ret)