linux-kernel - Re: + fix-spellings-of-slab-allocator-section-in-init-kconfig.patch added to -mm tree

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Date:	Wed, 09 May 2007 12:43:11 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Christoph Lameter <clameter@....com>
CC:	Matt Mackall <mpm@...enic.com>, akpm@...ux-foundation.org,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org
Subject: Re: + fix-spellings-of-slab-allocator-section-in-init-kconfig.patch
 added to -mm tree

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.
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