linux-kernel - Re: [PATCH 0/5] make slab gfp fair

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Message-Id: <1179350433.2912.66.camel@lappy>
Date:	Wed, 16 May 2007 23:20:33 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Christoph Lameter <clameter@....com>
Cc:	Matt Mackall <mpm@...enic.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Thomas Graf <tgraf@...g.ch>,
	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Phillips <phillips@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 0/5] make slab gfp fair

On Wed, 2007-05-16 at 14:13 -0700, Christoph Lameter wrote:
> On Wed, 16 May 2007, Peter Zijlstra wrote:
> > > How we know that we are out of trouble? Just try another alloc and see? If 
> > > that is the case then we may be failing allocations after the memory 
> > > situation has cleared up.
> > No, no, for each regular allocation we retry to populate ->cpu_slab with
> > a new slab. If that works we're out of the woods and the ->reserve_slab
> > is cleaned up.
> 
> Hmmm.. so we could simplify the scheme by storing the last rank 
> somewheres.

Not sure how that would help..

> If the alloc has less priority and we can extend the slab then
> clear up the situation.
> 
> If we cannot extend the slab then the alloc must fail.

That is exactly what is done; and as mpm remarked the other day, its a
binary system; we don't need full gfp fairness just ALLOC_NO_WATERMARKS.

And that is already found in ->reserve_slab; if present the last
allocation needed it; if not the last allocation was good.

> Could you put the rank into the page flags? On 64 bit at least there 
> should be enough space.

Current I stick the newly allocated page's rank in page->rank (yet
another overload of page->index). I've not yet seen the need to keep it
around longer.

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