From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751349AbdAWRDf (ORCPT ); Mon, 23 Jan 2017 12:03:35 -0500 Received: from mail-pg0-f67.google.com ([74.125.83.67]:33503 "EHLO mail-pg0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750723AbdAWRDe (ORCPT ); Mon, 23 Jan 2017 12:03:34 -0500 Date: Mon, 23 Jan 2017 12:03:29 -0500 From: Tejun Heo To: Mel Gorman Cc: Vlastimil Babka , 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: <20170123170329.GA7820@htj.duckdns.org> References: <20170117092954.15413-1-mgorman@techsingularity.net> <20170117092954.15413-4-mgorman@techsingularity.net> <06c39883-eff5-1412-a148-b063aa7bcc5f@suse.cz> <20170120152606.w3hb53m2w6thzsqq@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170120152606.w3hb53m2w6thzsqq@techsingularity.net> User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Fri, Jan 20, 2017 at 03:26:06PM +0000, Mel Gorman wrote: > > 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. This part of workqueue usage has always been a bit clunky and I should imrpove it but you don't necessarily have to pin the cpus from queueing to execution. You can queue without checking whether the CPU is online and instead synchronize the actual work item execution against cpu offline callback so that if the work item gets executed after offline callback is finished, it becomes a noop. Thanks. -- tejun