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Date: Mon, 14 May 2007 13:06:02 -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>,
       David Miller <davem@davemloft.net>,
       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 Mon, 14 May 2007, Peter Zijlstra wrote:

> > Hmmm.. Maybe we could do that.... But what I had in mind was simply to 
> > set a page flag (DebugSlab()) if you know in alloc_slab that the slab 
> > should be only used for emergency allocation. If DebugSlab is set then the
> > fastpath will not be called. You can trap all allocation attempts and 
> > insert whatever fancy logic you want in the debug path since its not 
> > performance critical.
> 
> I might have missed some detail when I looked at SLUB, but I did not see
> how setting SlabDebug would trap subsequent allocations to that slab.

Ok its not evident in slab_alloc. But if SlabDebug is set then 
page->lockless_list is always NULL and we always fall back to 
__slab_alloc. There we check for SlabDebug and go to the debug: label. 
There you can insert any fancy processing you want.