memcg: make oom less frequently

In previous implementation, mem_cgroup_try_charge checked the return
value of mem_cgroup_try_to_free_pages, and just retried if some pages
had been reclaimed.
But now, try_charge(and mem_cgroup_hierarchical_reclaim called from it)
only checks whether the usage is less than the limit.

This patch tries to change the behavior as before to cause oom less
frequently.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
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 322625f..fb62b43 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -773,10 +773,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
         * but there might be left over accounting, even after children
         * have left.
         */
-       ret = try_to_free_mem_cgroup_pages(root_mem, gfp_mask, noswap,
+       ret += try_to_free_mem_cgroup_pages(root_mem, gfp_mask, noswap,
                                           get_swappiness(root_mem));
        if (mem_cgroup_check_under_limit(root_mem))
-               return 0;
+               return 1;       /* indicate reclaim has succeeded */
        if (!root_mem->use_hierarchy)
                return ret;
 
@@ -787,10 +787,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
                        next_mem = mem_cgroup_get_next_node(root_mem);
                        continue;
                }
-               ret = try_to_free_mem_cgroup_pages(next_mem, gfp_mask, noswap,
+               ret += try_to_free_mem_cgroup_pages(next_mem, gfp_mask, noswap,
                                                   get_swappiness(next_mem));
                if (mem_cgroup_check_under_limit(root_mem))
-                       return 0;
+                       return 1;       /* indicate reclaim has succeeded */
                next_mem = mem_cgroup_get_next_node(root_mem);
        }
        return ret;
@@ -875,6 +875,8 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
 
                ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, gfp_mask,
                                                        noswap);
+               if (ret)
+                       continue;
 
                /*
                 * try_to_free_mem_cgroup_pages() might not give us a full