linux-kernel - Re: Re: Performance degradation seen after using one list for hot/cold pages.

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Message-id: <23853191.513591247115250186.JavaMail.weblogic@epml10>
Date:	Thu, 09 Jul 2009 04:54:10 +0000 (GMT)
From:	NARAYANAN GOPALAKRISHNAN <narayanan.g@...sung.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>
Cc:	"kamezawa.hiroyu@...fujitsu.com" <kamezawa.hiroyu@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"cl@...ux-foundation.org" <cl@...ux-foundation.org>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
	"stable@...nel.org" <stable@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: Re: Re: Performance degradation seen after using one list for hot/cold
 pages.


> I'll add the rather important text:
> 
> Fix a post-2.6.24 performance regression caused by
> 3dfa5721f12c3d5a441448086bee156887daa961 ("page-allocator: preserve PFN
> ordering when __GFP_COLD is set").
>
> This was a pretty major screwup.
>
> This is why changing core MM is so worrisome - there's so much secret and
> subtle history to it, and performance dependencies are unobvious and quite
> indirect and the lag time to discover regressions is long.
> 
> Narayanan, are you able to quantify the regression more clearly?  All I
> have is "2 MBps lower" which isn't very useful.  What is this as a
> percentage, and with what sort of disk controller?  Thanks.

It is around 15%. There is no disk controller as our setup is based on Samsung OneNAND
used as a memory mapped device on a OMAP2430 based board.

Narayanan