From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751870AbdAZAIE (ORCPT ); Wed, 25 Jan 2017 19:08:04 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:51544 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751112AbdAZAID (ORCPT ); Wed, 25 Jan 2017 19:08:03 -0500 Date: Wed, 25 Jan 2017 16:08:02 -0800 From: Andrew Morton To: Mel Gorman Cc: Tejun Heo , Vlastimil Babka , Linux Kernel , Linux-MM , Hillf Danton , Jesper Dangaard Brouer Subject: Re: [PATCH] mm, page_alloc: Use static global work_struct for draining per-cpu pages Message-Id: <20170125160802.67172878e6692e45fa035f37@linux-foundation.org> In-Reply-To: <20170125083038.rzb5f43nptmk7aed@techsingularity.net> References: <20170125083038.rzb5f43nptmk7aed@techsingularity.net> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 25 Jan 2017 08:30:38 +0000 Mel Gorman wrote: > As suggested by Vlastimil Babka and Tejun Heo, this patch uses a static > work_struct to co-ordinate the draining of per-cpu pages on the workqueue. > Only one task can drain at a time but this is better than the previous > scheme that allowed multiple tasks to send IPIs at a time. > > One consideration is whether parallel requests should synchronise against > each other. This patch does not synchronise for a global drain as the common > case for such callers is expected to be multiple parallel direct reclaimers > competing for pages when the watermark is close to min. Draining the per-cpu > list is unlikely to make much progress and serialising the drain is of > dubious merit. Drains are synchonrised for callers such as memory hotplug > and CMA that care about the drain being complete when the function returns. > > ... > > @@ -2402,24 +2415,16 @@ void drain_all_pages(struct zone *zone) > cpumask_clear_cpu(cpu, &cpus_with_pcps); > } > > - 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); > - } > - 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); > - } > + for_each_cpu(cpu, &cpus_with_pcps) { > + struct work_struct *work = per_cpu_ptr(&pcpu_drain, cpu); > + INIT_WORK(work, drain_local_pages_wq); It's strange to repeatedly run INIT_WORK() in this fashion. Overwriting an atomic_t which should already be zero, initializing a list_head which should already be in the initialized state... Can we instead do this a single time in init code? > + schedule_work_on(cpu, work); > } > + for_each_cpu(cpu, &cpus_with_pcps) > + flush_work(per_cpu_ptr(&pcpu_drain, cpu)); > + > put_online_cpus(); > + mutex_unlock(&pcpu_drain_mutex); > }