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

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Message-ID: <Pine.LNX.4.64.0705081920250.17931@schroedinger.engr.sgi.com>
Date:	Tue, 8 May 2007 19:24:07 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Matt Mackall <mpm@...enic.com>
cc:	akpm@...ux-foundation.org, Nick Piggin <nickpiggin@...oo.com.au>,
	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

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.

> average due to power of two cache sizes. So in both cases, less
> overhead than SLAB and different-sized objects can be comingled. SLUB
> would be awfully hard-pressed to have lower space overhead.

Its simple and easy to do and it was done in SLUB.
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