linux-kernel - Re: [PATCH 2/3][v2] vmstat: add anon_scan

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Date:	Mon, 18 Jan 2010 11:14:52 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 2/3][v2] vmstat: add anon_scan_ratio field to zoneinfo

> >> It can make stale data when high memory pressure happens.
> >
> > ?? why? and when?
> > I think it depend on what's stale mean.
> >
> > Currently(i.e. before the patch), get_scan_ratio have following fomula.
> > in such region, recent_scanned is not protected by zone->lru_lock.
> >
> >        ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1);
> >        ap /= reclaim_stat->recent_rotated[0] + 1;
> >        fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
> >        fp /= reclaim_stat->recent_rotated[1] + 1;
> >        percent[0] = 100 * ap / (ap + fp + 1);
> >        percent[1] = 100 - percent[0];
> >
> > It mean, shrink_zone() doesn't use exactly recent_scanned value. then
> > zoneinfo can use the same unexactly value.
> 
> Absoultely right. I missed that. Thanks.
> get_scan_ratio used lru_lock to get reclaim_stat->recent_xxxx.
> But, it doesn't used lru_lock to get ap/fp.
> 
> Is it intentional? I think you or Rik know it. :)
> I think if we want to get exact value, we have to use lru_lock until
> getting ap/fp.
> If it isn't, we don't need lru_lock when we get the reclaim_stat->recent_xxxx.
> 
> What do you think about it?

I believe the current code is intentional.



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