Re: [VM PATCH 2.6.8-rc1] Prevent excessive scanning of lower zone

[Shantanu Goel]

Hi Andrew,

--- Andrew Morton <akpm@xxxxxxxx> wrote:

> Shantanu Goel <sgoel01@xxxxxxxxx> wrote:
> >
> > I emailed this a few weeks back to the list but it
> > seems to have gotten lost...
> 
> It came through.  I was unable to reproduce the
> disproportional scanning
> rate on almost exactly the same setup, so I parked
> the problem for a while.
> 
> I do agree with the analysis though.  The problem
> _could_ occur.  I dunno
> why it happens for you and not for me...
> 

Actually, the analysis turned out to be not entirely
correct.  I think I have identified the offending
code.  Please see attached patch.  It makes kswapd()
skip zones which contain greater than "pages_high"
pages.

Machine setup is the same as before.
2x2.0Ghz Xeon w/HT, memory 256M (manually pegged).
I see this lopsided lower zone scanning on a dual
Opteron machine as well.

Attached are the kernbench results for stock 2.6.8-rc1
and 2.6.8-rc1 with patch.

Thanks,
Shantanu


		
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Attachment: vm.patch
Description: vm.patch

Attachment: kb-2.6.8-rc1
Description: kb-2.6.8-rc1

Attachment: kb-2.6.8-rc1-vmfix-latest10
Description: kb-2.6.8-rc1-vmfix-latest10