linux-kernel - Re: [patch 9/9] mm: keep page cache radix tree nodes in check

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Date:	Fri, 10 Jan 2014 18:09:25 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	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>,
	Mel Gorman <mgorman@...e.de>,
	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>,
	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 9/9] mm: keep page cache radix tree nodes in check

On 01/10/2014 01:10 PM, Johannes Weiner wrote:
> Previously, page cache radix tree nodes were freed after reclaim
> emptied out their page pointers.  But now reclaim stores shadow
> entries in their place, which are only reclaimed when the inodes
> themselves are reclaimed.  This is problematic for bigger files that
> are still in use after they have a significant amount of their cache
> reclaimed, without any of those pages actually refaulting.  The shadow
> entries will just sit there and waste memory.  In the worst case, the
> shadow entries will accumulate until the machine runs out of memory.
> 
> To get this under control, the VM will track radix tree nodes
> exclusively containing shadow entries on a per-NUMA node list.
> Per-NUMA rather than global because we expect the radix tree nodes
> themselves to be allocated node-locally and we want to reduce
> cross-node references of otherwise independent cache workloads.  A
> simple shrinker will then reclaim these nodes on memory pressure.

> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Reviewed-by: Rik van Riel <riel@...hat.com>

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