linux-kernel - Re: [-mm][PATCH 8/10] fix shmem page migration incorrectness on memcgroup

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Date:	Fri, 27 Jun 2008 16:57:56 +0900
From:	"MinChan Kim" <minchan.kim@...il.com>
To:	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>
Cc:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Lee Schermerhorn" <Lee.Schermerhorn@...com>,
	"Rik van Riel" <riel@...hat.com>,
	"Daisuke Nishimura" <nishimura@....nes.nec.co.jp>
Subject: Re: [-mm][PATCH 8/10] fix shmem page migration incorrectness on memcgroup

On Fri, Jun 27, 2008 at 2:41 PM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>> > mem_cgroup_uncharge() against old page is done after radix-tree-replacement.
>> > And there were special handling to ingore swap-cache page. But, shmem can
>> > be swap-cache and file-cache at the same time. Chekcing PageSwapCache() is
>> > not correct here. Check PageAnon() instead.
>>
>> When/How shmem can be both swap-cache and file-cache ?
>> I can't understand that situation.
>
> Hi
>
> see,
>
> shmem_writepage()
>   -> add_to_swap_cache()
>      -> SetPageSwapCache()
>
>
> BTW: his file-cache mean !Anon, not mean !SwapBacked.

Hi KOSAKI-san.
Thanks for explaining.

In the migrate_page_move_mapping, the page was already locked in unmap_and_move.
Also, we have a lock for that page for calling shmem_writepage.

So I think race problem between shmem_writepage and
migrate_page_move_mapping don't occur.
But I am not sure I am right.

If I am wrong, could you tell me when race problem happen ? :)


>
>



-- 
Kinds regards,
MinChan Kim
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