[PATCH 4/4] memcg: make oom less frequently

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

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.

ChangeLog: RFC->v1
- removed RETRIES_MAX.

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>
---
 mm/memcontrol.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 322625f..fb62b43 100644
--- 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

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