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Subject: Re: Maybe a VM bug in 2.4.18-18 from RH 8.0?
From: Arjan van de Ven <arjanv@redhat.com>
To: Andrew Morton <akpm@digeo.com>
Cc: linux-kernel@vger.kernel.org
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On Sat, 2002-12-07 at 01:01, Andrew Morton wrote:
> William Lee Irwin III wrote:
> > 
> > ...
> > A 16KB or 64KB kernel allocation unit would then annihilate
> 
> You want to be careful about this:
> 
> 	CPU: L1 I cache: 16K, L1 D cache: 16K
> 
> Because instantiating a 16k page into user pagetables in
> one hit means that it must all be zeroed.  With these large
> pagesizes that means that the application is likely to get
> 100% L1 misses against the new page, whereas it currently
> gets 100% hits.

If you really want you can cheat that 100% statistic into something much
lower by zeroing the page from back to front (based on the exact
faulting address even, because you know THAT one will get used) and/or
zeroing the second half while bypassing the cache. At least it's 50%
hits then ;)

Still not 100% and I still agree that the 8Kb number is much nicer for
16Kb L1 cache machines....
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