linux-kernel - Re: [PATCH 02/10] mm: system wide ALLOC_NO

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Date:	Mon, 06 Aug 2007 21:31:30 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Christoph Lameter <clameter@....com>
Cc:	Daniel Phillips <phillips@...nq.net>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Phillips <phillips@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Matt Mackall <mpm@...enic.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Steve Dickson <SteveD@...hat.com>
Subject: Re: [PATCH 02/10] mm: system wide ALLOC_NO_WATERMARK

On Mon, 2007-08-06 at 12:11 -0700, Christoph Lameter wrote:
> On Mon, 6 Aug 2007, Peter Zijlstra wrote:
> 
> > > > Shudder. That can just be a desaster for NUMA. Both performance wise
> > > > and logic wise. One cpuset being low on memory should not affect
> > > > applications in other cpusets.
> > 
> > Do note that these are only PF_MEMALLOC allocations that will break the
> > cpuset. And one can argue that these are not application allocation but
> > system allocations.
> 
> This is global, global locking etc etc. On a large NUMA system this will 
> cause significant delays. One fears that a livelock may result.

The only new lock is in SLUB, and I'm not aware of any regular
PF_MEMALLOC paths using slab allocations, but I'll instrument the
regular reclaim path to verify this.

The functionality this is aimed at is swap over network, and I doubt
you'll be enabling that on these machines.


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