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Date: Mon, 3 Jun 2013 10:25:33 +0200
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [patch 10/10] mm: workingset: keep shadow entries in check
Message-ID: <20130603082533.GH5910@twins.programming.kicks-ass.net>
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 <1369937046-27666-11-git-send-email-hannes@cmpxchg.org>
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To: Johannes Weiner <hannes@cmpxchg.org>
Cc: linux-mm@kvack.org, Andi Kleen <andi@firstfloor.org>, Andrea Arcangeli <aarcange@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Greg Thelen <gthelen@google.com>, Christoph Hellwig <hch@infradead.org>, Hugh Dickins <hughd@google.com>, Jan Kara <jack@suse.cz>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Mel Gorman <mgorman@suse.de>, Minchan Kim <minchan.kim@gmail.com>, Rik van Riel <riel@redhat.com>, Michel Lespinasse <walken@google.com>, Seth Jennings <sjenning@linux.vnet.ibm.com>, Roman Gushchin <klamm@yandex-team.ru>, metin d <metdos@yahoo.com>, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org

On Thu, May 30, 2013 at 02:04:06PM -0400, 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.
> 

Can't we simply prune all refault entries that have a distance larger
than the memory size? Then we must assume that no refault entry means
its too old, which I think is a fair assumption.

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