linux-kernel - Re: [RFC 2/3] vmscan hook

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Date:	Fri, 20 Jan 2012 09:24:49 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Minchan Kim <minchan@...nel.org>, linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, leonid.moiseichuk@...ia.com,
	penberg@...nel.org, mel@....ul.ie, rientjes@...gle.com,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ronen Hod <rhod@...hat.com>
Subject: Re: [RFC 2/3] vmscan hook

On Thu, 19 Jan 2012 09:42:59 -0500
Rik van Riel <riel@...hat.com> wrote:

> On 01/18/2012 09:25 PM, KAMEZAWA Hiroyuki wrote:
> > On Wed, 18 Jan 2012 09:17:17 -0500
> > Rik van Riel<riel@...hat.com>  wrote:
> >
> >> On 01/17/2012 07:18 PM, KAMEZAWA Hiroyuki wrote:
> >>> On Wed, 18 Jan 2012 08:08:01 +0900
> >>> Minchan Kim<minchan@...nel.org>   wrote:
> >>>
> >>>>>>> 2. can't we measure page-in/page-out distance by recording something ?
> >>>>>>
> >>>>>> I can't understand your point. What's relation does it with swapout prevent?
> >>>>>>
> >>>>>
> >>>>> If distance between pageout ->   pagein is short, it means thrashing.
> >>>>> For example, recoding the timestamp when the page(mapping, index) was
> >>>>> paged-out, and check it at page-in.
> >>>>
> >>>> Our goal is prevent swapout. When we found thrashing, it's too late.
> >>>
> >>> If you want to prevent swap-out, don't swapon any. That's all.
> >>> Then, you can check the number of FILE_CACHE and have threshold.
> >>
> >> I think you are getting hung up on a word here.
> >>
> >> As I understand it, the goal is to push out the point where
> >> we start doing heavier swap IO, allowing us to overcommit
> >> memory more heavily before things start really slowing down.
> >>
> >
> > Yes.
> >
> > Hmm, considering that the issue is slow down,
> >
> > time values as
> >
> > - 'cpu time used for memory reclaim'
> > - 'latency of page allocation'
> > - 'application execution speed' ?
> >
> > may be a better score to see rather than just seeing lru's stat.
> 
> I believe those all qualify as "too late".
> 
> We want to prevent things from becoming bad, for as long
> as we (easily) can.
> 

Hmm, then some threshold-notifier interface will be required.
Problem is how to know free + page_can_be_freed_without_risk.

Thanks,
-Kame

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