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 12:02:29 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	David Miller <davem@...emloft.net>
CC:	clameter@....com, mpm@...enic.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: + fix-spellings-of-slab-allocator-section-in-init-kconfig.patch
 added to -mm tree

David Miller wrote:
> From: Christoph Lameter <clameter@....com>
> Date: Tue, 8 May 2007 18:32:35 -0700 (PDT)
> 
> 
>>That SLUB cannot do. And I do not believe you. SLOB must have some way to 
>>distinguish the objects and their sizes since kfree does not include size 
>>information. You can mix slabs of different size on the same page without 
>>metadata. Magic?
>>
>>So how does kfree then know how to free the object? There must be some way 
>>where you get the metainformation. What is the point of your 8 byte 
>>metadata that keeps getting inserted? That does not consume memory on a 
>>page?
> 
> 
> SLOB uses metadata, but that metadata seemingly only needs to be
> uptodate in freed objects.
> 
> SLOB seems to look at the descriptor in the previous blob to figure
> out how big the being-freed blob is.  That's actually kind of clever
> :-)

You know how big the being-freed blob is because the kmem cache structure
contains that. The free metadata is just needed for free area management.

BTW, we _really_ should be doing RCU properly in slob, because you
technically can't noop RCU on UP (even though the current users may be
safe...).

Patch attached to do that.

-- 
SUSE Labs, Novell Inc.

View attachment "slob-add-rcu.patch" of type "text/plain" (2957 bytes)