linux-kernel - Re: [patch 04/10] mm: shmem: save one radix tree lookup when truncating swapped pages

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Message-ID: <20140212111103.GR6732@suse.de>
Date:	Wed, 12 Feb 2014 11:11:03 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Bob Liu <bob.liu@...cle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Dave Chinner <david@...morbit.com>,
	Greg Thelen <gthelen@...gle.com>,
	Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Luigi Semenzato <semenzato@...gle.com>,
	Metin Doslu <metin@...usdata.com>,
	Michel Lespinasse <walken@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Ozgun Erdogan <ozgun@...usdata.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Roman Gushchin <klamm@...dex-team.ru>,
	Ryan Mallon <rmallon@...il.com>, Tejun Heo <tj@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 04/10] mm: shmem: save one radix tree lookup when
 truncating swapped pages

On Mon, Feb 03, 2014 at 07:53:36PM -0500, Johannes Weiner wrote:
> Page cache radix tree slots are usually stabilized by the page lock,
> but shmem's swap cookies have no such thing.  Because the overall
> truncation loop is lockless, the swap entry is currently confirmed by
> a tree lookup and then deleted by another tree lookup under the same
> tree lock region.
> 
> Use radix_tree_delete_item() instead, which does the verification and
> deletion with only one lookup.  This also allows removing the
> delete-only special case from shmem_radix_tree_replace().
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Reviewed-by: Minchan Kim <minchan@...nel.org>
> Reviewed-by: Rik van Riel <riel@...hat.com>

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs
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