linux-kernel - Re: [PATCH 0/3] Unmapped page cache control (v5)

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Message-Id: <20110401222250.A894.A69D9226@jp.fujitsu.com>
Date:	Fri,  1 Apr 2011 22:21:26 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	kosaki.motohiro@...fujitsu.com, linux-mm@...ck.org,
	akpm@...ux-foundation.org, npiggin@...nel.dk, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, cl@...ux.com,
	kamezawa.hiroyu@...fujitsu.com, Mel Gorman <mel@....ul.ie>,
	Minchan Kim <minchan.kim@...il.com>
Subject: Re: [PATCH 0/3] Unmapped page cache control (v5)

> * KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> [2011-04-01 16:56:57]:
> 
> > Hi
> > 
> > > > 1) zone reclaim doesn't work if the system has multiple node and the
> > > >    workload is file cache oriented (eg file server, web server, mail server, et al). 
> > > >    because zone recliam make some much free pages than zone->pages_min and
> > > >    then new page cache request consume nearest node memory and then it
> > > >    bring next zone reclaim. Then, memory utilization is reduced and
> > > >    unnecessary LRU discard is increased dramatically.
> > > > 
> > > >    SGI folks added CPUSET specific solution in past. (cpuset.memory_spread_page)
> > > >    But global recliam still have its issue. zone recliam is HPC workload specific 
> > > >    feature and HPC folks has no motivation to don't use CPUSET.
> > > 
> > > I am afraid you misread the patches and the intent. The intent to
> > > explictly enable control of unmapped pages and has nothing
> > > specifically to do with multiple nodes at this point. The control is
> > > system wide and carefully enabled by the administrator.
> > 
> > Hm. OK, I may misread.
> > Can you please explain the reason why de-duplication feature need to selectable and
> > disabled by defaut. "explicity enable" mean this feature want to spot corner case issue??
> 
> Yes, because given a selection of choices (including what you
> mentioned in the review), it would be nice to have
> this selectable.

It's no good answer. :-/
Who need the feature and who shouldn't use it? It this enough valuable for enough large
people? That's my question point.



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