Date: Thu, 08 Apr 2004 16:42:37 -0700
From: "Martin J. Bligh" <mbligh@aracnet.com>
To: Andrea Arcangeli <andrea@suse.de>
cc: linux-kernel@vger.kernel.org
Subject: Re: -mmX 4G patches feedback [numbers: how much performance impact]
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--On Friday, April 09, 2004 01:22:15 +0200 Andrea Arcangeli <andrea@suse.de> wrote:

> On Thu, Apr 08, 2004 at 04:14:08PM -0700, Martin J. Bligh wrote:
>> Me confused. Are you saying it's worse compared to pte_highmem? or to 
>> shoving ptes in lowmem?
> 
> worse than pte_highmem if booting with mem=800m
> 
>> Ah. You're worried about the distro situation, where PTE_HIGHMEM would
>> be turned on for a non-highmem machine, right? Makes more sense I guess.
> 
> it's not just a distro situation, it's about not having to recompile the
> kernel for every machine I own, even gentoo has an option to have a
> compile server in the network that build packages and you install the
> binaries from it, so there must be some value in being able to share a
> binary on more than one machine (this is especially true for me since I
> upgrade kernel quite fast).
> 
> it's not just about non-highmem machines, on 1G/2G boxes the probability
> that pte-highmem cause you any slowdown is an order of magnitude smaller
> than on a 32G machine (where ptes should never hit lowmem or it means my
> classzone lowmem_reserve_ratio algorithms have not yet been ported to 2.6)
> with your model you'd have no way to boost when you are lucky to get a
> lowmem page.

OK, I think I understand your concern now - I was being slow ;-)
I guess there are a few more PTEs to set up on exec, you're right.
I still think it's faster than pte_highmem, which was a static config 
option anyway (so it's better in all cases than pte_highmem, when enabled)
but still not perfect. Hmm. I'll go think about it ;-)

m.

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