Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH 2/3][v2] vmstat: add anon_scan_ratio field to zoneinfo | Date | Mon, 18 Jan 2010 10:54:21 +0900 (JST) |
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> Hi, KOSAKI. > > On Mon, Jan 18, 2010 at 10:04 AM, KOSAKI Motohiro > <kosaki.motohiro@jp.fujitsu.com> wrote: > >> Hi, KOSAKI. > >> > >> On Thu, Jan 14, 2010 at 2:18 PM, KOSAKI Motohiro > >> <kosaki.motohiro@jp.fujitsu.com> 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. > > It has a primary role that floating average as well as prevenitng overflow. :) > So, It's important. > > > > > if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) { > > spin_lock_irq(&zone->lru_lock); > > reclaim_stat->recent_scanned[0] /= 2; > > reclaim_stat->recent_rotated[0] /= 2; > > spin_unlock_irq(&zone->lru_lock); > > } > > > > > > So, I don't think current implementation can show stale data. > > 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.
> Moreever, I don't want to make complicate thing(ie, need_update) > than old if it doesn't have some benefit.(I think lru_lock isn't big overhead)
Hmm.. I think lru_lock can makes big overhead.
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