linux-kernel - Re: Default zone_reclaim_mode = 1 on NUMA kernel is bad forfile/email/web servers

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Date:	Mon, 27 Sep 2010 11:01:41 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	kosaki.motohiro@...fujitsu.com, Rob Mueller <robm@...tmail.fm>,
	linux-kernel@...r.kernel.org, Bron Gondwana <brong@...tmail.fm>,
	linux-mm <linux-mm@...ck.org>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: Default zone_reclaim_mode = 1 on NUMA kernel is bad forfile/email/web servers

Hi

> No doubt this is true. The only real difference is that there are more NUMA
> machines running mail/web/file servers now than there might have been in the
> past. The default made sense once upon a time. Personally I wouldn't mind
> the default changing but my preference would be that distribution packages
> installing on NUMA machines would prompt if the default should be changed if it
> is likely to be of benefit for that package (e.g. the mail, file and web ones).

At first impression, I thought this is cute idea. But, after while thinking, I've found some
weak point. The problem is, too many package need to disable zone_reclaim_mode.
zone_reclaim doesn't works fine if an application need large working set rather than
local node size. It mean major desktop applications (e.g. OpenOffice.org, Firefox, GIMP)
need to disable zone_reclaim. It mean even though basic package installation require 
zone_reclaim disabling. Then, this mechanism doesn't works practically. Even though
the user hope to use the machine for hpc, disable zone_reclaim will be turn on anyway.

Probably, opposite switch (default is zone_reclaim=0, and installation MPI library change
to zone_reclaim=1) might works. but I can guess why you don't propose this one.

Hmm....

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