Date: Fri, 5 Mar 2004 12:41:19 -0800
From: Andrew Morton <akpm@osdl.org>
To: Andrea Arcangeli <andrea@suse.de>
Cc: mbligh@aracnet.com, mingo@elte.hu, peter@mysql.com, riel@redhat.com,
       linux-kernel@vger.kernel.org
Subject: Re: 2.4.23aa2 (bugfixes and important VM improvements for the high
 end)
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Andrea Arcangeli <andrea@suse.de> wrote:
>
> > > The main thing you didn't mention is the overhead in the per-cpu data
>  > > structures, that alone generates an overhead of several dozen mbytes
>  > > only in the page allocator, without accounting the slab caches,
>  > > pagetable caches etc.. putting an high limit to the per-cpu caches
>  > > should make a 32-way 32G work fine with 3:1 too though. 8-way is
>  > > fine with 32G currently.
>  > 
>  > Humpf. Do you have a hard figure on how much it actually is per cpu?
> 
>  not a definitive one, but it's sure more than 2m per cpu, could be 3m
>  per cpu.

It'll average out to 68 pages per cpu.  (4 in ZONE_DMA, 64 in ZONE_NORMAL).

That's eight megs on 32-way.  Maybe it can be trimmed back a bit, but on
32-way you probably want the locking amortisation more than the 8 megs.

The settings we have in there are still pretty much guesswork.  I don't
think anyone has done any serious tuning on them.  Any differences are
likely to be small.


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