From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935093AbeEWXRk (ORCPT ); Wed, 23 May 2018 19:17:40 -0400 Received: from mail-yb0-f193.google.com ([209.85.213.193]:35375 "EHLO mail-yb0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934770AbeEWXRj (ORCPT ); Wed, 23 May 2018 19:17:39 -0400 X-Google-Smtp-Source: AB8JxZpBc+Tqegrkx3Nn73Dhf/1D5PNMsUa+JrMXZYAfUN8KvVSqpHFZZ814uPOJbAMbEMJ7GxXjQA== Date: Wed, 23 May 2018 16:17:36 -0700 From: Tejun Heo To: Rik van Riel Cc: Jens Axboe , linux-kernel@vger.kernel.org, "Paul E. McKenney" , Jan Kara , Andrew Morton , kernel-team@fb.com Subject: Re: [PATCH] bdi: Move cgroup bdi_writeback to a dedicated low concurrency workqueue Message-ID: <20180523231736.GT1718769@devbig577.frc2.facebook.com> References: <20180523175632.GO1718769@devbig577.frc2.facebook.com> <1527112995.7898.31.camel@surriel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1527112995.7898.31.camel@surriel.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Rik. On Wed, May 23, 2018 at 06:03:15PM -0400, Rik van Riel wrote: > Dumb question. Does setting max_active to 1 mean > that every cgwb_release_workfn() ends up forcing > another RCU grace period on the whole system, while > today you might have a bunch of them waiting on the > same RCU grace period advance? > > Would it be faster to have some number (up to 16?) > push RCU once, at the same time, instead of having > each of them push RCU into a next grace period one > after another? Oh yeah, you're absolutely right. This would end up doing a lot of back-to-back synchronize_rcu_expedited() calls which can't be good. I'll send a patch to push it upto 16. Thanks. -- tejun