From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755419AbaGOP4I (ORCPT ); Tue, 15 Jul 2014 11:56:08 -0400 Received: from mail-wg0-f50.google.com ([74.125.82.50]:46918 "EHLO mail-wg0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751748AbaGOP4E (ORCPT ); Tue, 15 Jul 2014 11:56:04 -0400 Date: Tue, 15 Jul 2014 17:56:00 +0200 From: Michal Hocko To: Johannes Weiner Cc: Andrew Morton , Hugh Dickins , Tejun Heo , Vladimir Davydov , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch 13/13] mm: memcontrol: rewrite uncharge API Message-ID: <20140715155600.GA29269@dhcp22.suse.cz> References: <1403124045-24361-1-git-send-email-hannes@cmpxchg.org> <1403124045-24361-14-git-send-email-hannes@cmpxchg.org> <20140715082545.GA9366@dhcp22.suse.cz> <20140715142350.GD9366@dhcp22.suse.cz> <20140715150937.GS29639@cmpxchg.org> <20140715151818.GE9366@dhcp22.suse.cz> <20140715154643.GT29639@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140715154643.GT29639@cmpxchg.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 15-07-14 11:46:43, Johannes Weiner wrote: > On Tue, Jul 15, 2014 at 05:18:18PM +0200, Michal Hocko wrote: > > On Tue 15-07-14 11:09:37, Johannes Weiner wrote: > > > On Tue, Jul 15, 2014 at 04:23:50PM +0200, Michal Hocko wrote: > > > > On Tue 15-07-14 10:25:45, Michal Hocko wrote: > > [...] > > > > > @@ -2760,15 +2752,15 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg, > > > > > spin_unlock_irq(&zone->lru_lock); > > > > > } > > > > > > > > > > - mem_cgroup_charge_statistics(memcg, page, anon, nr_pages); > > > > > - unlock_page_cgroup(pc); > > > > > - > > > > > + local_irq_disable(); > > > > > + mem_cgroup_charge_statistics(memcg, page, nr_pages); > > > > > /* > > > > > * "charge_statistics" updated event counter. Then, check it. > > > > > * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree. > > > > > * if they exceeds softlimit. > > > > > */ > > > > > memcg_check_events(memcg, page); > > > > > + local_irq_enable(); > > > > > > > > preempt_{enable,disbale} should be sufficient for > > > > mem_cgroup_charge_statistics and memcg_check_events no? > > > > The first one is about per-cpu accounting (and that should be atomic > > > > wrt. IRQ on the same CPU) and the later one uses IRQ safe locks down in > > > > mem_cgroup_update_tree. > > > > > > How could it be atomic wrt. IRQ on the local CPU when IRQs that modify > > > the counters can fire on the local CPU? > > > > I meant that __this_atomic_add and __this_cpu_inc should be atomic wrt. IRQ. > > We do not care that an IRQ might jump in between two per-cpu operations. > > This is racy from other CPUs anyway. > > It's really about a single RMW (+=) being interrupted by an IRQ. > this_cpu_ guarantees IRQ-atomicity, but __this_cpu_ does not. Yes, you are right. I was too x86 centric where both add and inc are really a single instruction. Generic implementation already shows I was wrong. Sorry for the noise! -- Michal Hocko SUSE Labs