linux-kernel - Re: [PATCH] vmscan: limit concurrent reclaimers in shrink

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Message-ID: <20091214161944.GB16474@basil.fritz.box>
Date:	Mon, 14 Dec 2009 17:19:44 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Larry Woodman <lwoodman@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Rik van Riel <riel@...hat.com>,
	kosaki.motohiro@...fujitsu.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	aarcange@...hat.com
Subject: Re: [PATCH] vmscan: limit concurrent reclaimers in shrink_zone

On Mon, Dec 14, 2009 at 09:23:19AM -0500, Larry Woodman wrote:
> On Mon, 2009-12-14 at 14:08 +0100, Andi Kleen wrote:
> > Rik van Riel <riel@...hat.com> writes:
> > 
> > > +max_zone_concurrent_reclaim:
> > > +
> > > +The number of processes that are allowed to simultaneously reclaim
> > > +memory from a particular memory zone.
> > > +
> > > +With certain workloads, hundreds of processes end up in the page
> > > +reclaim code simultaneously.  This can cause large slowdowns due
> > > +to lock contention, freeing of way too much memory and occasionally
> > > +false OOM kills.
> > > +
> > > +To avoid these problems, only allow a smaller number of processes
> > > +to reclaim pages from each memory zone simultaneously.
> > > +
> > > +The default value is 8.
> > 
> > I don't like the hardcoded number. Is the same number good for a 128MB
> > embedded system as for as 1TB server?  Seems doubtful.
> > 
> > This should be perhaps scaled with memory size and number of CPUs?
> 
> Remember this a per-zone number.

A zone could be 64MB or 32GB. And the system could have 1 or 1024 CPUs.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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