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Date: Wed, 24 Feb 2010 12:52:53 -0800
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [patch 36/36] khugepaged
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To: Rik van Riel <riel@redhat.com>
Cc: aarcange@redhat.com, linux-mm@kvack.org, Marcelo Tosatti <mtosatti@redhat.com>, Adam Litke <agl@us.ibm.com>, Avi Kivity <avi@redhat.com>, Izik Eidus <ieidus@redhat.com>, Hugh Dickins <hugh.dickins@tiscali.co.uk>, Nick Piggin <npiggin@suse.de>, Mel Gorman <mel@csn.ul.ie>, Dave Hansen <dave@linux.vnet.ibm.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Ingo Molnar <mingo@elte.hu>, Mike Travis <travis@sgi.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Christoph Lameter <cl@linux-foundation.org>, Chris Wright <chrisw@sous-sol.org>, bpicco@redhat.com, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Balbir Singh <balbir@linux.vnet.ibm.com>, Arnd Bergmann <arnd@arndb.de>
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On Wed, 24 Feb 2010 15:28:44 -0500 Rik van Riel <riel@redhat.com> wrote:

> > Generally it seems like a bad idea to do this sort of thing
> > asynchronously.  Because it reduces repeatability across runs and
> > across machines - system behaviour becomes more dependent on the size
> > of the machine and the amount of activity in unrelated jobs?
> 
> Isn't system performance already dependent on the size of
> the machine and the amount of activity in unrelated jobs?

I said "repeatability".

> Using hugepages is a performance enhancement only and
> otherwise transparent to userspace.

And it's bad that a job run will take a varying amount of CPU time due
to unrelated activity.  Yes, that can already happen, but it's
undesirable and it's undesirable to worsen things.

If this work could be done synchronously then runtimes become more
consistent, which is a good thing.

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