Re: [PATCH 2/3][v2] vmstat: add anon_scan_ratio field to zoneinfo

From: KOSAKI Motohiro
Date: Sun Jan 17 2010 - 20:04:28 EST

> On Thu, Jan 14, 2010 at 2:18 PM, KOSAKI Motohiro
> <kosaki.motohiro@xxxxxxxxxxxxxx> wrote:
> >> > Well. zone->lock and zone->lru_lock should be not taked at the same time.
> >>
> >> I looked over the code since I am out of office.
> >> I can't find any locking problem zone->lock and zone->lru_lock.
> >> Do you know any locking order problem?
> >> Could you explain it with call graph if you don't mind?
> >>
> >> I am out of office by tomorrow so I can't reply quickly.
> >> Sorry for late reponse.
> >
> > This is not lock order issue. both zone->lock and zone->lru_lock are
> > hotpath lock. then, same tame grabbing might cause performance impact.
> Sorry for late response.
> Your patch makes get_anon_scan_ratio of zoneinfo stale.
> What you said about performance impact is effective when VM pressure high.
> I think stale data is all right normally.
> But when VM pressure is high and we want to see the information in zoneinfo(
> this case is what you said), stale data is not a good, I think.
> If it's not a strong argue, I want to use old get_scan_ratio
> in get_anon_scan_ratio.

please looks such function again.

usally we use recent_rotated/recent_scanned ratio. then following
decreasing doesn't change any scan-ratio meaning. it only prevent
stat overflow.

if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
reclaim_stat->recent_scanned[0] /= 2;
reclaim_stat->recent_rotated[0] /= 2;

So, I don't think current implementation can show stale data.


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