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Message-ID: <49368DAF.9060206@redhat.com>
Date: Wed, 03 Dec 2008 08:46:23 -0500
From: Rik van Riel <riel@...hat.com>
To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC: akpm@...ux-foundation.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, mel@....ul.ie
Subject: Re: [PATCH] vmscan: improve reclaim throuput to bail out patch
KOSAKI Motohiro wrote:
> Hi
>
> I evaluate rvr bailout and skip-freeing patch in this week conteniously.
> I'd like to dump first output here.
>
>
>
> Rik, could you please review following?
> ==
> vmscan bail out patch move nr_reclaimed variable to struct scan_control.
> Unfortunately, indirect access can easily happen cache miss.
> More unfortunately, Some architecture (e.g. ia64) don't access global
> variable so fast.
That is amazing. Especially considering that the scan_control
is a local variable on the stack.
> if heavy memory pressure happend, that's ok.
> cache miss already plenty. it is not observable.
>
> but, if memory pressure is lite, performance degression is obserbable.
> about 4-5% degression.
>
> Then, this patch introduce temporal local variable.
> OK. the degression is disappeared.
I can't argue with the numbers, though :)
Maybe all the scanning we do ends up evicting the cache lines
with the scan_control struct in it from the fast part of the
CPU cache?
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Acked-by: Rik van Riel <riel@...hat.com>
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