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From: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Date: Mon, 9 Jan 2012 11:49:14 -0500
Message-ID: <CAHGf_=ovR8Mwagaa2PpjEfjKpuqjvPdWX5Uy=Tyi2+B480WUBA@mail.gmail.com>
Subject: Re: [PATCH] mm: vmscan: recompute page status when putting back
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To: Hillf Danton <dhillf@gmail.com>
Cc: linux-mm@kvack.org, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, David Rientjes <rientjes@google.com>, Andrew Morton <akpm@linux-foundation.org>, LKML <linux-kernel@vger.kernel.org>

> If unlikely the given page is isolated from lru list again, its status is
> recomputed before putting back to lru list, since the comment says page's
> status can change while we move it among lru.
>
>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Hillf Danton <dhillf@gmail.com>
> ---
>
> --- a/mm/vmscan.c =A0 =A0 =A0 Thu Dec 29 20:20:16 2011
> +++ b/mm/vmscan.c =A0 =A0 =A0 Fri Jan =A06 21:31:56 2012
> @@ -633,12 +633,14 @@ int remove_mapping(struct address_space
> =A0void putback_lru_page(struct page *page)
> =A0{
> =A0 =A0 =A0 =A0int lru;
> - =A0 =A0 =A0 int active =3D !!TestClearPageActive(page);
> - =A0 =A0 =A0 int was_unevictable =3D PageUnevictable(page);
> + =A0 =A0 =A0 int active;
> + =A0 =A0 =A0 int was_unevictable;
>
> =A0 =A0 =A0 =A0VM_BUG_ON(PageLRU(page));
>
> =A0redo:
> + =A0 =A0 =A0 active =3D !!TestClearPageActive(page);
> + =A0 =A0 =A0 was_unevictable =3D PageUnevictable(page);
> =A0 =A0 =A0 =A0ClearPageUnevictable(page);

When and How do this race happen?

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