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Date: Wed, 09 May 2007 12:43:11 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Christoph Lameter <clameter@sgi.com>
CC: Matt Mackall <mpm@selenic.com>, akpm@linux-foundation.org,
       David Miller <davem@davemloft.net>, linux-kernel@vger.kernel.org
Subject: Re: + fix-spellings-of-slab-allocator-section-in-init-kconfig.patch
 added to -mm tree
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Christoph Lameter wrote:
> On Tue, 8 May 2007, Matt Mackall wrote:
> 
> 
>>>>Yes. It can in fact put 512 8-byte objects in a 4k page. More
>>>
>>>So can SLUB.
>>
>>Not without at least a bit per-object of overhead. So you can either
>>fit 512 objects in 4160 bytes or 504 objects in 4k.
> 
> 
> Slub uses a linked list pointer in the page struct which is NULL if all 
> objects are allocated. There is no bit per object overhead.
> 
> 
>>For the kmalloc case, we do have an 8-byte header, which works out to
>>be about 1/8th of the slop that mainline kmalloc over SLAB has on
> 
> 
> Exactly. That overhead does not exist in SLUB. Thus SLOB is less efficient 
> than SLUB.

What you trade for that is that one page page can only serve one slab.
For small systems, I would not be surprised if that was less space
efficient, even just looking at kmalloc caches in isolation. Or do you
have numbers to support your conclusion?

-- 
SUSE Labs, Novell Inc.