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Date: Fri, 10 Jan 2014 18:09:25 -0500
From: Rik van Riel <riel@redhat.com>
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To: Johannes Weiner <hannes@cmpxchg.org>,
        Andrew Morton <akpm@linux-foundation.org>
CC: Andi Kleen <andi@firstfloor.org>, Andrea Arcangeli <aarcange@redhat.com>,
        Bob Liu <bob.liu@oracle.com>, Christoph Hellwig <hch@infradead.org>,
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        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Luigi Semenzato <semenzato@google.com>, Mel Gorman <mgorman@suse.de>,
        Metin Doslu <metin@citusdata.com>,
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        linux-kernel@vger.kernel.org
Subject: Re: [patch 9/9] mm: keep page cache radix tree nodes in check
References: <1389377443-11755-1-git-send-email-hannes@cmpxchg.org> <1389377443-11755-10-git-send-email-hannes@cmpxchg.org>
In-Reply-To: <1389377443-11755-10-git-send-email-hannes@cmpxchg.org>
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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@cmpxchg.org>

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

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