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

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Date:	Fri,  9 Mar 2012 17:46:11 -0500
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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: Re: [PATCH] memcg: revert fix to mapcount check for this release

On Fri, Mar 09, 2012 at 01:37:32PM -0800, Hugh Dickins wrote:
> 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.

Agreed. We should rethink whole design rather than detail.

> 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>

Reviewed-by: Naoya Horiguchi <n-horiguchi@...jp.nec.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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