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References: <20110928081452.GC23535@redhat.com> <1317290085-3804-1-git-send-email-minchan.kim@gmail.com>
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Date: Thu, 29 Sep 2011 21:50:02 +0900
Message-ID: <CAHGf_=rH4QThPidf9TD_d1qt3QJ-_mAJnH+XmP+ZJ0pOjpOTTQ@mail.gmail.com>
Subject: Re: [PATCH v2] vmscan: add barrier to prevent evictable page in
 unevictable list
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To: Minchan Kim <minchan.kim@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-mm <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>, Johannes Weiner <jweiner@redhat.com>, Mel Gorman <mel@csn.ul.ie>, Rik van Riel <riel@redhat.com>, Lee Schermerhorn <lee.schermerhorn@hp.com>

2011/9/29 Minchan Kim <minchan.kim@gmail.com>:
> When racing between putback_lru_page and shmem_lock with lock=3D0 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
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0clear_bit(=
AS_UNEVICTABLE)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0spin_lock
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if PageLRU=
()
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0if !test_bit(AS_UNEVICTABLE)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 =A0move evictable list
> smp_mb
> if !test_bit(AS_UNEVICTABLE)
> =A0 =A0 =A0 =A0move evictable list
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0spin_unloc=
k
>
> But, pagevec_lookup in scan_mapping_unevictable_pages has rcu_read_[un]lo=
ck so
> it could protect reordering before reaching test_bit(AS_UNEVICTABLE) on p=
rocessor #1
> so this problem never happens. But it's a unexpected side effect and we s=
hould
> solve this problem properly.
>
> This patch adds a barrier after mapping_clear_unevictable.
>
> side-note: I didn't meet this problem but just found during review.
>
> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Cc: Mel Gorman <mel@csn.ul.ie>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
> Acked-by: Johannes Weiner <jweiner@redhat.com>
> Signed-off-by: Minchan Kim <minchan.kim@gmail.com>

  Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

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