From: Oliver Neukum <oliver@neukum.org>
To: Arjan van de Ven <arjan@infradead.org>
Subject: Re: [2.6 patch] i386: always use 4k stacks
Date: Fri, 16 Dec 2005 20:14:35 +0100
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Cc: Brian Gerst <bgerst@didntduck.org>, linux-kernel@vger.kernel.org
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Am Freitag, 16. Dezember 2005 20:02 schrieb Arjan van de Ven:
> 
> > 
> > So what about arches where single-page stacks aren't viable (for example 
> > x86_64)?  Are we just screwed?
> 
> 
> x86 is specially handicapped due to the fact that the stacks need to be
> in the lowmem zone. Even if you have 8Gb ram, the lowmem zone is still
> 800Mb and a bit, and this gets to be under a high pressure, like
> hyper-fragmentation. Same for bounce buffers etc etc.
> 
> note that the order thing is by far not the only advantage, pure memory
> usage alone and cache locality also are wins. The memory usage halves
> for kernel stacks after all (which means you can do more threads in
> java, or use the memory for disk cache ;)

1. Cache usage depends on actual stack usage. How much you allocate
doesn't matter
2. You are surely getting a cache effect by using interrupt stacks. Which
is larger?
3. When you use kmalloc instead of the stack you are reducing locality.

	Regards
		Oliver
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