linux-kernel - Re: [PATCH] Implement slub fastpath in terms of freebase and freeoffset

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Message-ID: <Pine.LNX.4.64.0802291155480.11292@schroedinger.engr.sgi.com>
Date:	Fri, 29 Feb 2008 11:57:16 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	Eric Dumazet <dada1@...mosbay.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Torsten Kaiser <just.for.lkml@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Implement slub fastpath in terms of freebase and freeoffset

On Fri, 29 Feb 2008, Mathieu Desnoyers wrote:

> > Then we do not need the page->end field anymore right? I will try 
> > to rediff your patch against current slab-mm and see how we can proceed 
> > from there.
> 
> I guess you could replace page->end with the (expensive)
> page_address(page) + 1 in new_slab.
> 
> You would also have to change slab_address() to use
> page_address(page). Since this is used by check_valid_pointer, I am not
> sure it's a good idea to use this slow operation there.
> 
> Or maybe you have a different alternative in mind ?

page->end was introduced to have a unique pointer for each slab. The 
counter that you introduces can take over that role. So we could use a 
NULL pointer again as the end of the objects? Or some constant?

I am going to revert the change that introduced page->end for 2.6.25 since 
it seems that the new fastpath does not need this. It was specific to the 
old fastpath.

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