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

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Message-Id: <20070709095116.c2ea700f.akpm@linux-foundation.org>
Date:	Mon, 9 Jul 2007 09:51:16 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, linux-mm@...r.kernel.org,
	suresh.b.siddha@...el.com, corey.d.gough@...el.com,
	Pekka Enberg <penberg@...helsinki.fi>,
	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

On Mon, 9 Jul 2007 09:06:46 -0700 (PDT) Christoph Lameter <clameter@....com> wrote:

> But yes the power of 
> two caches are a necessary design feature of SLAB/SLUB that allows O(1) 
> operations of kmalloc slabs which in turns causes memory wastage because 
> of rounding of the alloc to the next power of two.

I've frequently wondered why we don't just create more caches for kmalloc:
make it denser than each-power-of-2-plus-a-few-others-in-between.

I assume the tradeoff here is better packing versus having a ridiculous
number of caches.  Is there any other cost?

Because even having 1024 caches wouldn't consume a terrible amount of
memory and I bet it would result in aggregate savings.

Of course, a scheme which creates kmalloc caches on-demand would be better,
but that would kill our compile-time cache selection, I suspect.
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