linux-kernel - Re: [patch] mm, compaction: avoid isolating pinned pages fix

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Message-ID: <20140204021533.GA14924@lge.com>
Date:	Tue, 4 Feb 2014 11:15:33 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch] mm, compaction: avoid isolating pinned pages fix

On Mon, Feb 03, 2014 at 06:00:56PM -0800, David Rientjes wrote:
> On Tue, 4 Feb 2014, Joonsoo Kim wrote:
> 
> > Okay. It can't fix your situation. Anyway, *normal* anon pages may be mapped
> > and have positive page_count(), so your code such as
> > '!page_mapping(page) && page_count(page)' makes compaction skip these *normal*
> > anon pages and this is incorrect behaviour.
> > 
> 
> So how does that work with migrate_page_move_mapping() which demands 
> page_count(page) == 1 and the get_page_unless_zero() in 
> __isolate_lru_page()?

Before doing migrate_page_move_mapping(), try_to_unmap() is called so that all
mapping is unmapped. Then, remained page_count() is 1 which is grabbed by
__isolate_lru_page(). Am I missing something?

Thanks.
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