linux-kernel - Re: [patch 10/10] mm: workingset: keep shadow entries in check

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Date:	Mon, 3 Jun 2013 19:10:31 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	linux-mm@...ck.org, Andi Kleen <andi@...stfloor.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Thelen <gthelen@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan.kim@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Michel Lespinasse <walken@...gle.com>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Roman Gushchin <klamm@...dex-team.ru>,
	metin d <metdos@...oo.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [patch 10/10] mm: workingset: keep shadow entries in check

On Mon, Jun 03, 2013 at 11:01:54AM -0400, Johannes Weiner wrote:
> On Mon, Jun 03, 2013 at 10:22:09AM +0200, Peter Zijlstra wrote:
> > On Thu, May 30, 2013 at 02:04:06PM -0400, Johannes Weiner wrote:
> > > 2. a list of files that contain shadow entries is maintained.  If the
> > >    global number of shadows exceeds a certain threshold, a shrinker is
> > >    activated that reclaims old entries from the mappings.  This is
> > >    heavy-handed but it should not be a common case and is only there
> > >    to protect from accidentally/maliciously induced OOM kills.
> > 
> > Grrr.. another global files list. We've been trying rather hard to get
> > rid of the first one :/
> > 
> > I see why you want it but ugh.
> 
> I'll try to make it per-SB like the inode list.  It probably won't be
> per-SB shrinkers because of the global nature of the shadow limit, but
> at least per-SB inode lists should be doable.

per have per-cpu-per-sb lists, see file_sb_list_{add,del} and
do_file_list_for_each_entry()

> > I have similar worries for your global time counter, large machines
> > might thrash on that one cacheline.
> 
> Fair enough.
> 
> So I'm trying the following idea: instead of the global time counter,
> have per-zone time counters and store the zone along with those local
> timestamps in the shadow entries (nid | zid | time).  On refault, we
> can calculate the zone-local distance first and then use the inverse
> of the zone's eviction proportion to scale it to a global distance.

The thinking is since that's the same granularity as the zone lock,
you're likely to at least trash the zone lock in equal measure?
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