linux-kernel - Re: [PATCH] vmscan: add barrier to prevent evictable page in unevictable list

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Message-ID: <4E828AFC.7070405@jp.fujitsu.com>
Date:	Wed, 28 Sep 2011 11:48:28 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	minchan.kim@...il.com
CC:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, jweiner@...hat.com, mel@....ul.ie,
	riel@...hat.com, lee.schermerhorn@...com
Subject: Re: [PATCH] vmscan: add barrier to prevent evictable page in unevictable
 list

(2011/09/28 11:25), Minchan Kim wrote:
> On Wed, Sep 28, 2011 at 11:21:58AM +0900, KOSAKI Motohiro wrote:
>> (2011/09/28 10:45), Minchan Kim wrote:
>>> When racing between putback_lru_page and shmem_unlock happens,
>>> progrom execution order is as follows, but clear_bit in processor #1
>>> could be reordered right before spin_unlock of processor #1.
>>> Then, the page would be stranded on the unevictable list.
>>>
>>> spin_lock
>>> SetPageLRU
>>> spin_unlock
>>>                                 clear_bit(AS_UNEVICTABLE)
>>>                                 spin_lock
>>>                                 if PageLRU()
>>>                                         if !test_bit(AS_UNEVICTABLE)
>>>                                         	move evictable list
>>> smp_mb
>>> if !test_bit(AS_UNEVICTABLE)
>>>         move evictable list
>>>                                 spin_unlock
>>>
>>> But, pagevec_lookup in scan_mapping_unevictable_pages has rcu_read_[un]lock so
>>> it could protect reordering before reaching test_bit(AS_UNEVICTABLE) on processor #1
>>> so this problem never happens. But it's a unexpected side effect and we should
>>> solve this problem properly.
>>
>> Do we still need this after Hannes removes scan_mapping_unevictable_pages?
>  
> Hi KOSAKI,
> 
> What Hannes removes is scan_zone_unevictable_pages not scan_mapping_unevictable_pages.
> 

Oops, you are right.



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