linux-kernel - Re: [PATCH 02/10] mm: vmscan: Obey proportional scanning requirements for kswapd

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Date:	Thu, 11 Apr 2013 10:09:09 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Rik van Riel <riel@...hat.com>,
	Zlatko Calusic <zcalusic@...sync.net>,
	Johannes Weiner <hannes@...xchg.org>,
	dormando <dormando@...ia.net>,
	Satoru Moriya <satoru.moriya@....com>,
	Michal Hocko <mhocko@...e.cz>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/10] mm: vmscan: Obey proportional scanning
 requirements for kswapd

On Thu, Apr 11, 2013 at 09:14:19AM +0900, Kamezawa Hiroyuki wrote:
> >
> >nr[lru] at the end there is pages remaining to be scanned not pages
> >scanned already.
> 
> yes.
> 
> >Did you mean something like this?
> >
> >nr[lru] = scantarget[lru] * percentage / 100 - (scantarget[lru] - nr[lru])
> >
> 
> For clarification, this "percentage" means the ratio of remaining scan target of
> another LRU. So, *scanned* percentage is "100 - percentage", right ?
> 

Yes, correct.

> If I understand the changelog correctly, you'd like to keep
> 
>    scantarget[anon] : scantarget[file]
>    == really_scanned_num[anon] : really_scanned_num[file]
> 

Yes.

> even if we stop scanning in the middle of scantarget. And you introduced "percentage"
> to make sure that both scantarget should be done in the same ratio.
> 

Yes.

> So...another lru should scan  scantarget[x] * (100 - percentage)/100 in total.
> 
> nr[lru] = scantarget[lru] * (100 - percentage)/100 - (scantarget[lru] - nr[lru])
>           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^    ^^^^^^^^^^^^^^^^^^^^^^^^^
>              proportionally adjusted scan target        already scanned num
> 
>        =  nr[lru] - scantarget[lru] * percentage/100.
> 

Yes, you are completely correct. This preserves the original ratio of
anon:file scanning properly.

-- 
Mel Gorman
SUSE Labs
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