From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id CEC8C6B006A for ; Sun, 17 Jan 2010 21:10:59 -0500 (EST) Received: by pzk34 with SMTP id 34so1920117pzk.11 for ; Sun, 17 Jan 2010 18:10:57 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20100118104910.AE2D.A69D9226@jp.fujitsu.com> References: <20100118100359.AE22.A69D9226@jp.fujitsu.com> <28c262361001171747w450c8fd8j4daf84b72fb68e1a@mail.gmail.com> <20100118104910.AE2D.A69D9226@jp.fujitsu.com> Date: Mon, 18 Jan 2010 11:10:56 +0900 Message-ID: <28c262361001171810w544614b7rdd3df0f984692f35@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: I missed Cc. On Mon, Jan 18, 2010 at 10:54 AM, KOSAKI Motohiro wrote: >> 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 s= ame 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 ar= e >> >> > hotpath lock. then, same tame grabbing might cause performance impa= ct. >> >> >> >> 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 zo= neinfo( >> >> 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 overfl= ow. :) >> 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(&= zone->lru_lock); >> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0reclaim_stat->r= ecent_scanned[0] /=3D 2; >> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0reclaim_stat->r= ecent_rotated[0] /=3D 2; >> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0spin_unlock_irq= (&zone->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. > > ?? 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. > > =C2=A0 =C2=A0 =C2=A0 =C2=A0ap =3D (anon_prio + 1) * (reclaim_stat->recent= _scanned[0] + 1); > =C2=A0 =C2=A0 =C2=A0 =C2=A0ap /=3D reclaim_stat->recent_rotated[0] + 1; > =C2=A0 =C2=A0 =C2=A0 =C2=A0fp =3D (file_prio + 1) * (reclaim_stat->recent= _scanned[1] + 1); > =C2=A0 =C2=A0 =C2=A0 =C2=A0fp /=3D reclaim_stat->recent_rotated[1] + 1; > =C2=A0 =C2=A0 =C2=A0 =C2=A0percent[0] =3D 100 * ap / (ap + fp + 1); > =C2=A0 =C2=A0 =C2=A0 =C2=A0percent[1] =3D 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_xx= xx. What do you think about it? > > >> 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 ove= rhead) > > Hmm.. > I think lru_lock can makes big overhead. I don't want to argue strongly about this. That's because i don't have seen that. If you have a conern about lru_lock, I don't opposed your patch. --=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