From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752854AbdATPeB (ORCPT ); Fri, 20 Jan 2017 10:34:01 -0500 Received: from outbound-smtp07.blacknight.com ([46.22.139.12]:45507 "EHLO outbound-smtp07.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752796AbdATPd7 (ORCPT ); Fri, 20 Jan 2017 10:33:59 -0500 Date: Fri, 20 Jan 2017 15:26:06 +0000 From: Mel Gorman To: Vlastimil Babka Cc: Andrew Morton , Linux Kernel , Linux-MM , Hillf Danton , Jesper Dangaard Brouer , Petr Mladek Subject: Re: [PATCH 3/4] mm, page_alloc: Drain per-cpu pages from workqueue context Message-ID: <20170120152606.w3hb53m2w6thzsqq@techsingularity.net> References: <20170117092954.15413-1-mgorman@techsingularity.net> <20170117092954.15413-4-mgorman@techsingularity.net> <06c39883-eff5-1412-a148-b063aa7bcc5f@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <06c39883-eff5-1412-a148-b063aa7bcc5f@suse.cz> User-Agent: Mutt/1.6.2 (2016-07-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 20, 2017 at 03:26:05PM +0100, Vlastimil Babka wrote: > > @@ -2392,8 +2404,24 @@ void drain_all_pages(struct zone *zone) > > else > > cpumask_clear_cpu(cpu, &cpus_with_pcps); > > } > > - on_each_cpu_mask(&cpus_with_pcps, (smp_call_func_t) drain_local_pages, > > - zone, 1); > > + > > + if (works) { > > + for_each_cpu(cpu, &cpus_with_pcps) { > > + struct work_struct *work = per_cpu_ptr(works, cpu); > > + INIT_WORK(work, drain_local_pages_wq); > > + schedule_work_on(cpu, work); > > This translates to queue_work_on(), which has the comment of "We queue > the work to a specific CPU, the caller must ensure it can't go away.", > so is this safe? lru_add_drain_all() uses get_online_cpus() around this. > get_online_cpus() would be required. > schedule_work_on() also uses the generic system_wq, while lru drain has > its own workqueue with WQ_MEM_RECLAIM so it seems that would be useful > here as well? > I would be reluctant to introduce a dedicated queue unless there was a definite case where an OOM occurred because pages were pinned on per-cpu lists and couldn't be drained because the buddy allocator was depleted. As it was, I thought the fallback case was excessively paranoid. > > + } > > + for_each_cpu(cpu, &cpus_with_pcps) > > + flush_work(per_cpu_ptr(works, cpu)); > > + } else { > > + for_each_cpu(cpu, &cpus_with_pcps) { > > + struct work_struct work; > > + > > + INIT_WORK(&work, drain_local_pages_wq); > > + schedule_work_on(cpu, &work); > > + flush_work(&work); > > Totally out of scope, but I wonder if schedule_on_each_cpu() could use > the same fallback that's here? > I'm not aware of a case where it really has been a problem. I only considered it here as the likely caller is in a context that is failing allocations. -- Mel Gorman SUSE Labs