From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753565AbaGOPSa (ORCPT ); Tue, 15 Jul 2014 11:18:30 -0400 Received: from cantor2.suse.de ([195.135.220.15]:55231 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750990AbaGOPSV (ORCPT ); Tue, 15 Jul 2014 11:18:21 -0400 Date: Tue, 15 Jul 2014 17:18:18 +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: <20140715151818.GE9366@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140715150937.GS29639@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 11:09:37, 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. > > > > @@ -780,11 +780,14 @@ static int move_to_new_page(struct page *newpage, struct page *page, > > > rc = fallback_migrate_page(mapping, newpage, page, mode); > > > > > > if (rc != MIGRATEPAGE_SUCCESS) { > > > - newpage->mapping = NULL; > > > + if (!PageAnon(newpage)) > > > + newpage->mapping = NULL; > > > > OK, I am probably washed out from looking into this for too long but I > > cannot figure why have you done this... > > mem_cgroup_uncharge() relies on PageAnon() working. Usually, anon > pages retain their page->mapping until they hit the page allocator, > the exception was old migration pages. OK, got it now. I was suprised by a change in !memcg path. Maybe this is worth a comment? -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [patch 13/13] mm: memcontrol: rewrite uncharge API Date: Tue, 15 Jul 2014 17:18:18 +0200 Message-ID: <20140715151818.GE9366@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> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20140715150937.GS29639@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 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. > > > > @@ -780,11 +780,14 @@ static int move_to_new_page(struct page *newpage, struct page *page, > > > rc = fallback_migrate_page(mapping, newpage, page, mode); > > > > > > if (rc != MIGRATEPAGE_SUCCESS) { > > > - newpage->mapping = NULL; > > > + if (!PageAnon(newpage)) > > > + newpage->mapping = NULL; > > > > OK, I am probably washed out from looking into this for too long but I > > cannot figure why have you done this... > > mem_cgroup_uncharge() relies on PageAnon() working. Usually, anon > pages retain their page->mapping until they hit the page allocator, > the exception was old migration pages. OK, got it now. I was suprised by a change in !memcg path. Maybe this is worth a comment? -- Michal Hocko SUSE Labs -- 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