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Date: Mon, 9 Jul 2007 14:04:24 +0300
From: "Pekka Enberg" <penberg@cs.helsinki.fi>
To: "Nick Piggin" <nickpiggin@yahoo.com.au>
Subject: Re: [patch 09/10] Remove the SLOB allocator for 2.6.23
Cc: "Andrew Morton" <akpm@linux-foundation.org>, "Ingo Molnar" <mingo@elte.hu>,
       "Christoph Lameter" <clameter@sgi.com>, linux-kernel@vger.kernel.org,
       linux-mm@vger.kernel.org, suresh.b.siddha@intel.com,
       corey.d.gough@intel.com, "Matt Mackall" <mpm@selenic.com>,
       "Denis Vlasenko" <vda.linux@googlemail.com>,
       "Erik Andersen" <andersen@codepoet.org>
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Hi Nick,

On 7/9/07, Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> SLOB contains several significant O(1) and also O(n) memory savings that
> are so far impossible-by-design for SLUB. They are: slab external
> fragmentation is significantly reduced; kmalloc internal fragmentation is
> significantly reduced; order of magnitude smaller kmem_cache data type;
> order of magnitude less code...

I assume with "slab external fragmentation" you mean allocating a
whole page for a slab when there are not enough objects to fill the
whole thing thus wasting memory? We could try to combat that by
packing multiple variable-sized slabs within a single page. Also,
adding some non-power-of-two kmalloc caches might help with internal
fragmentation.

In any case, SLUB needs some serious tuning for smaller machines
before we can get rid of SLOB.