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Date: Wed, 16 May 2007 13:59:04 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
cc: Matt Mackall <mpm@selenic.com>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, Thomas Graf <tgraf@suug.ch>,
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       Andrew Morton <akpm@linux-foundation.org>,
       Daniel Phillips <phillips@google.com>,
       Pekka Enberg <penberg@cs.helsinki.fi>
Subject: Re: [PATCH 0/5] make slab gfp fair
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On Wed, 16 May 2007, Peter Zijlstra wrote:

> > I do not see any distinction between DMA and regular memory. If we need 
> > DMA memory to complete the transaction then this wont work?
> 
> If network relies on slabs that are cpuset constrained and the page
> allocator reserves do not match that, then yes, it goes bang.

So if I put a 32 bit network card in a 64 bit system -> bang?

> > Is there some indicator somewhere that indicates that we are in trouble? I 
> > just see the ranks.
> 
> Yes, and page->rank will only ever be 0 if the page was allocated with
> ALLOC_NO_WATERMARKS, and that only ever happens if we're in dire
> straights and entitled to it.
> 
> Otherwise it'll be ALLOC_WMARK_MIN or somesuch.

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.