linux-kernel - [patch rfc] memcg: remove NULL check from lookup_page

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Message-ID: <20110203141230.GG2286@cmpxchg.org>
Date:	Thu, 3 Feb 2011 15:12:30 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [patch rfc] memcg: remove NULL check from lookup_page_cgroup() result

The page_cgroup array is set up before even fork is initialized.  I
seriously doubt that this code executes before the array is alloc'd.

Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 mm/memcontrol.c |    5 +----
 1 files changed, 1 insertions(+), 4 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a145c9e..6abaa10 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2343,10 +2343,7 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
 	}
 
 	pc = lookup_page_cgroup(page);
-	/* can happen at boot */
-	if (unlikely(!pc))
-		return 0;
-	prefetchw(pc);
+	BUG_ON(!pc); /* XXX: remove this and move pc lookup into commit */
 
 	ret = __mem_cgroup_try_charge(mm, gfp_mask, &mem, oom, page_size);
 	if (ret || !mem)
-- 
1.7.4
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