linux-kernel - [patch] memcg: fix unit mismatch in memcg oom limit calculation

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Message-ID: <20101109110521.GS23393@cmpxchg.org>
Date:	Tue, 9 Nov 2010 12:05:21 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	David Rientjes <rientjes@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <balbir@...ibm.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Greg Thelen <gthelen@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [patch] memcg: fix unit mismatch in memcg oom limit calculation

Adding the number of swap pages to the byte limit of a memory control
group makes no sense.  Convert the pages to bytes before adding them.

The only user of this code is the OOM killer, and the way it is used
means that the error results in a higher OOM badness value.  Since the
cgroup limit is the same for all tasks in the cgroup, the error should
have no practical impact at the moment.

But let's not wait for future or changing users to trip over it.

Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 mm/memcontrol.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1552,8 +1552,9 @@ u64 mem_cgroup_get_limit(struct mem_cgro
 	u64 limit;
 	u64 memsw;
 
-	limit = res_counter_read_u64(&memcg->res, RES_LIMIT) +
-			total_swap_pages;
+	limit = res_counter_read_u64(&memcg->res, RES_LIMIT);
+	limit += total_swap_pages << PAGE_SHIFT;
+
 	memsw = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
 	/*
 	 * If memsw is finite and limits the amount of swap space available
--
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