linux-kernel - [PATCH] memcg: revert fix to mapcount check for this release

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Date:	Fri, 9 Mar 2012 13:37:32 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hillf Danton <dhillf@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH] memcg: revert fix to mapcount check for this release

Respectfully revert commit e6ca7b89dc76 "memcg: fix mapcount check
in move charge code for anonymous page" for the 3.3 release, so that
it behaves exactly like releases 2.6.35 through 3.2 in this respect.

Horiguchi-san's commit is correct in itself, 1 makes much more sense
than 2 in that check; but it does not go far enough - swapcount
should be considered too - if we really want such a check at all.

We appear to have reached agreement now, and expect that 3.4 will
remove the mapcount check, but had better not make 3.3 different.

Signed-off-by: Hugh Dickins <hughd@...gle.com>
---

 mm/memcontrol.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 3.3-rc6+/mm/memcontrol.c	2012-03-05 22:03:45.940000832 -0800
+++ linux/mm/memcontrol.c	2012-03-09 13:06:41.716250093 -0800
@@ -5075,7 +5075,7 @@ static struct page *mc_handle_present_pt
 		return NULL;
 	if (PageAnon(page)) {
 		/* we don't move shared anon */
-		if (!move_anon() || page_mapcount(page) > 1)
+		if (!move_anon() || page_mapcount(page) > 2)
 			return NULL;
 	} else if (!move_file())
 		/* we ignore mapcount for file pages */
--
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