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Date: Fri, 4 May 2007 09:23:04 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
cc: Pekka Enberg <penberg@cs.helsinki.fi>, linux-kernel@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, Peter Zijlstra wrote:

> On Fri, 2007-05-04 at 09:09 -0700, Christoph Lameter wrote:
> > On Fri, 4 May 2007, Pekka Enberg wrote:
> > 
> > > On 5/4/07, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> > > > Expost buffer_size in order to allow fair estimates on the actual space
> > > > used/needed.
> > 
> > We already have ksize?
> 
> ksize gives the internal size, whereas these give the external size.
> 
> I need to know how much space I need to reserve, hence I need the
> external size; whereas normally you want to know how much space you have
> available, which is what ksize gives.
> 
> Didn't we have this discussion last time?

I was cced on that as far as I can tell.

The name objsize suggests the size of the object not the slab size.
If you want this then maybe call it kmem_cache_slab_size. SLUB 
distinguishes between obj_size which is the size of the struct that is 
used and slab_size which is the size of the object after alignment, adding 
debug information etc etc. See also slabinfo.c for a way to calculate 
theses sizes from user space.

If we really drop SLAB then we wont need this. SLUBs data structures are 
not opaque.