linux-kernel - Re: [PATCH 09/10] Change table chaining layout

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Message-ID: <471D3C26.3020807@garzik.org>
Date:	Mon, 22 Oct 2007 20:11:18 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Matt Mackall <mpm@...enic.com>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	mingo@...e.hu, Linux/m68k <linux-m68k@...r.kernel.org>
Subject: Re: [PATCH 09/10] Change table chaining layout

Matt Mackall wrote:
> On Mon, Oct 22, 2007 at 11:52:51PM +0100, Alan Cox wrote:
>> On Mon, 22 Oct 2007 16:47:07 -0500
>> Matt Mackall <mpm@...enic.com> wrote:
>>
>>> On Mon, Oct 22, 2007 at 05:21:30PM -0400, Jeff Garzik wrote:
>>>> Alan Cox wrote:
>>>>> Why can't we just make the list one item longer than the entry count and
>>>>> stick a NULL on the end of it like normal people ?
>>>> Certainly seems safer than the current "let's run off the end of the 
>>>> list if anything bad happens" setup...  And I do not think allocating 
>>>> n+1 scatterlist entries will have much of a negative impact.
>>> It'll mean m-1 scatterlists fit on a slab.
>> Is that really a credible space issue ?
> 
> Yes. Especially if m is 2 or 1. A scatterlist on 64-bit x86 looks like
> it takes 32 bytes, which means 128 elements fit on a page. One more
> spills - ouch!

  ...and its trivial to reduce that number to 127 without noticeable 
effect, really.

	Jeff



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