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Date: Fri, 4 May 2007 12:59:44 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
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To: Pekka Enberg <penberg@cs.helsinki.fi>
cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, netdev@vger.kernel.org,
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       Mike Christie <michaelc@cs.wisc.edu>,
       Andrew Morton <akpm@linux-foundation.org>,
       Daniel Phillips <phillips@google.com>
Subject: Re: [PATCH 08/40] mm: kmem_cache_objsize
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On Fri, 4 May 2007, Pekka Enberg wrote:

> Christoph Lameter wrote:
> > On Fri, 4 May 2007, Pekka Enberg wrote:
> > 
> > > Again, slab has no way of actually estimating how many pages you need for
> > > a
> > > given number of objects. So we end up calculating some upper bound which
> > > doesn't belong in mm/slab.c. I am perfectly okay with:
> > 
> > It can give a worst case number and that is what he wants.
> 
> Sure. But he can calculate that elsewhere instead of bringing it in mm/slab.c
> where it's no use for anyone else...

He is not able to calculate it just using the object size since he does 
not know where the slab put the slab management structure. And in case of 
SLUB there is no slab management structure... Which means he would have to 
special case based on the slab allocator selected.