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

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Message-ID: <alpine.DEB.2.02.1402031610090.10778@chino.kir.corp.google.com>
Date:	Mon, 3 Feb 2014 17:20:46 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....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: [patch] mm, compaction: avoid isolating pinned pages fix

On Tue, 4 Feb 2014, Joonsoo Kim wrote:

> I think that you need more code to skip this type of page correctly.
> Without page_mapped() check, this code makes migratable pages be skipped,
> since if page_mapped() case, page_count() may be more than zero.
> 
> So I think that you need following change.
> 
> (!page_mapping(page) && !page_mapped(page) && page_count(page))
> 

These pages returned by get_user_pages() will have a mapcount of 1 so this 
wouldn't actually fix the massive lock contention.  page_mapping() is only 
going to be NULL for pages off the lru like these are for 
PAGE_MAPPING_ANON.
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