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Date: Mon, 18 Jan 2010 10:04:15 +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 > Hi, KOSAKI. > > On Thu, Jan 14, 2010 at 2:18 PM, KOSAKI Motohiro > <kosaki.motohiro@...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. 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. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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