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

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Date:	Wed, 28 Sep 2011 11:25:10 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.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

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.

-- 
Kinds regards,
Minchan Kim
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