linux-kernel - Re: [RFC][PATCH] page reclaim throttle take2

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Date:	Wed, 27 Feb 2008 14:00:42 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	balbir@...ux.vnet.ibm.com, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Rik van Riel <riel@...hat.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [RFC][PATCH] page reclaim throttle take2

On Wed, 27 Feb 2008 13:45:18 +0900
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> Hi
> 
> > One more thing, I would request you to add default heuristics (number of
> > reclaimers), based on the number of cpus in the system. Letting people tuning it
> > is fine, but defaults should be related to number of cpus, nodes and zones on
> > the system. Zones can be reaped in parallel per node and cpus allow threads to
> > run in parallel. So please use that to come up with good defaults, instead of a
> > number like "3".
> 
> I don't think so.
> all modern many cpu machine stand on NUMA.
> it mean following,
>  - if cpu increases, then zone increases, too.
> 
> if default value increase by #cpus, lock contension dramatically increase
> on large numa.
> 
> Have I overlooked anything?
> 
> 
How about adding something like..
== 
CONFIG_SIMULTANEOUS_PAGE_RECLAIMERS 
int
default 3
depends on DEBUG
help
  This value determines the number of threads which can do page reclaim
  in a zone simultaneously. If this is too big, performance under heavy memory
  pressure will decrease.
  If unsure, use default.
==

Then, you can get performance reports from people interested in this
feature in test cycle.

Thanks,
-Kame


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