From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx122.postini.com [74.125.245.122]) by kanga.kvack.org (Postfix) with SMTP id 2C1CD6B004D for ; Mon, 23 Jan 2012 17:05:35 -0500 (EST) Received: by qcsg1 with SMTP id g1so853611qcs.14 for ; Mon, 23 Jan 2012 14:05:34 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20120119085309.616cadb4.kamezawa.hiroyu@jp.fujitsu.com> References: <20120113173001.ee5260ca.kamezawa.hiroyu@jp.fujitsu.com> <20120113174019.8dff3fc1.kamezawa.hiroyu@jp.fujitsu.com> <20120117164605.GB22142@tiehlicka.suse.cz> <20120118091226.b46e0f6e.kamezawa.hiroyu@jp.fujitsu.com> <20120118104703.GA31112@tiehlicka.suse.cz> <20120119085309.616cadb4.kamezawa.hiroyu@jp.fujitsu.com> Date: Mon, 23 Jan 2012 14:05:33 -0800 Message-ID: Subject: Re: [RFC] [PATCH 3/7 v2] memcg: remove PCG_MOVE_LOCK flag from pc->flags From: Ying Han Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: KAMEZAWA Hiroyuki Cc: Michal Hocko , "linux-mm@kvack.org" , "hugh.dickins@tiscali.co.uk" , "hannes@cmpxchg.org" , cgroups@vger.kernel.org, "bsingharora@gmail.com" On Wed, Jan 18, 2012 at 3:53 PM, KAMEZAWA Hiroyuki wrote: > On Wed, 18 Jan 2012 11:47:03 +0100 > Michal Hocko wrote: > >> On Wed 18-01-12 09:12:26, KAMEZAWA Hiroyuki wrote: >> > On Tue, 17 Jan 2012 17:46:05 +0100 >> > Michal Hocko wrote: >> > >> > > On Fri 13-01-12 17:40:19, KAMEZAWA Hiroyuki wrote: >> [...] >> > > > This patch removes PCG_MOVE_LOCK and add hashed rwlock array >> > > > instead of it. This works well enough. Even when we need to >> > > > take the lock, >> > > >> > > Hmmm, rwlocks are not popular these days very much. >> > > Anyway, can we rather make it (source) memcg (bit)spinlock instead. = We >> > > would reduce false sharing this way and would penalize only pages fr= om >> > > the moving group. >> > > >> > per-memcg spinlock ? >> >> Yes >> >> > The reason I used rwlock() is to avoid disabling IRQ. =A0This routine >> > will be called by IRQ context (for dirty ratio support). =A0So, IRQ >> > disable will be required if we use spinlock. >> >> OK, I have missed the comment about disabling IRQs. It's true that we do >> not have to be afraid about deadlocks if the lock is held only for >> reading from the irq context but does the spinlock makes a performance >> bottleneck? We are talking about the slowpath. >> I could see the reason for the read lock when doing hashed locks because >> they are global but if we make the lock per memcg then we shouldn't >> interfere with other updates which are not blocked by the move. >> > > Hm, ok. In the next version, I'll use per-memcg spinlock (with hash if ne= cessary) Just want to make sure I understand it, even we make the lock per-memcg, there is still a false sharing of pc within one memcg. Do we need to demonstrate the effect ? Also, I don't get the point of why spinlock instead of rwlock in this case? --Ying > > Thanks, > -Kame > > -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org