From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id 04BEA6B006A for ; Sun, 17 Jan 2010 20:47:21 -0500 (EST) Received: by pwj10 with SMTP id 10so1772656pwj.6 for ; Sun, 17 Jan 2010 17:47:20 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20100118100359.AE22.A69D9226@jp.fujitsu.com> References: <20100114141735.672B.A69D9226@jp.fujitsu.com> <28c262361001150923l138f6805t22546887bf81b283@mail.gmail.com> <20100118100359.AE22.A69D9226@jp.fujitsu.com> Date: Mon, 18 Jan 2010 10:47:20 +0900 Message-ID: <28c262361001171747w450c8fd8j4daf84b72fb68e1a@mail.gmail.com> Subject: Re: [PATCH 2/3][v2] vmstat: add anon_scan_ratio field to zoneinfo From: Minchan Kim Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: LKML , linux-mm , Andrew Morton , Balbir Singh , KAMEZAWA Hiroyuki , Rik van Riel List-ID: Hi, KOSAKI. On Mon, Jan 18, 2010 at 10:04 AM, KOSAKI Motohiro wrote: >> Hi, KOSAKI. >> >> On Thu, Jan 14, 2010 at 2:18 PM, KOSAKI Motohiro >> 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 hig= h. >> I think stale data is all right normally. >> But when VM pressure is high and we want to see the information in zonei= nfo( >> 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. > > =C2=A0 =C2=A0 =C2=A0 =C2=A0if (unlikely(reclaim_stat->recent_scanned[0] >= anon / 4)) { > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0spin_lock_irq(&zon= e->lru_lock); > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0reclaim_stat->rece= nt_scanned[0] /=3D 2; > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0reclaim_stat->rece= nt_rotated[0] /=3D 2; > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0spin_unlock_irq(&z= one->lru_lock); > =C2=A0 =C2=A0 =C2=A0 =C2=A0} > > > So, I don't think current implementation can show stale data. It can make stale data when high memory pressure happens. > > Thanks. > 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 overhe= ad) --=20 Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org