[PATCH RFC] mm/memcg: recalculate chargeable space after waiting migrating charges

[Wanpeng Li <liwp.linux@gmail.com>]

From: Wanpeng Li <liwp@linux.vnet.ibm.com>

Function mem_cgroup_do_charge will call mem_cgroup_reclaim,
there are two break points in mem_cgroup_reclaim:
if (total && (flag & MEM_CGROUP_RECLAIM_SHIRINK))
	break;
if (mem_cgroup_margin(memcg))
	break;
so mem_cgroup_reclaim can't guarantee reclaim enough pages(nr_pages) 
which is requested from mem_cgroup_do_charge, if mem_cgroup_margin
(mem_over_limit) >= nr_pages is not true, the process will go to
mem_cgroup_wait_acct_move to wait doubly charge counted caused by
task move. But this time still can't guarantee enough pages(nr_pages) is
ready, directly return CHARGE_RETRY is incorret. We should add a check
to confirm enough pages is ready, otherwise go to oom.

Signed-off-by: Wanpeng Li <liwp.linux@gmail.com>
---
 mm/memcontrol.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f72b5e5..4ae3848 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2210,7 +2210,8 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	 * At task move, charge accounts can be doubly counted. So, it's
 	 * better to wait until the end of task_move if something is going on.
 	 */
-	if (mem_cgroup_wait_acct_move(mem_over_limit))
+	if (mem_cgroup_wait_acct_move(mem_over_limit)
+			&& mem_cgroup_margin(mem_over_limit) >= nr_pages)
 		return CHARGE_RETRY;
 
 	/* If we don't need to call oom-killer at el, return immediately */
-- 
1.7.5.4

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