linux-kernel - Re: [patch 09/10] Remove the SLOB allocator for 2.6.23

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Message-ID: <84144f020707090404l657a62c7x89d7d06b3dd6c34b@mail.gmail.com>
Date:	Mon, 9 Jul 2007 14:04:24 +0300
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Nick Piggin" <nickpiggin@...oo.com.au>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Christoph Lameter" <clameter@....com>,
	linux-kernel@...r.kernel.org, linux-mm@...r.kernel.org,
	suresh.b.siddha@...el.com, corey.d.gough@...el.com,
	"Matt Mackall" <mpm@...enic.com>,
	"Denis Vlasenko" <vda.linux@...glemail.com>,
	"Erik Andersen" <andersen@...epoet.org>
Subject: Re: [patch 09/10] Remove the SLOB allocator for 2.6.23

Hi Nick,

On 7/9/07, Nick Piggin <nickpiggin@...oo.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.
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