From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752013Ab1HBHYr (ORCPT ); Tue, 2 Aug 2011 03:24:47 -0400 Received: from mx1.fusionio.com ([66.114.96.30]:50003 "EHLO mx1.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751743Ab1HBHYm (ORCPT ); Tue, 2 Aug 2011 03:24:42 -0400 X-ASG-Debug-ID: 1312269881-03d6a510a9224340001-xx1T2L X-Barracuda-Envelope-From: JAxboe@fusionio.com Message-ID: <4E37A638.2020304@fusionio.com> Date: Tue, 2 Aug 2011 09:24:40 +0200 From: Jens Axboe MIME-Version: 1.0 To: Vivek Goyal CC: linux kernel mailing list , "Israel G. Lugo" Subject: Re: [PATCH] cfq-iosched: Reduce linked group count upon group destruction References: <20110801184702.GF3805@redhat.com> X-ASG-Orig-Subj: Re: [PATCH] cfq-iosched: Reduce linked group count upon group destruction In-Reply-To: <20110801184702.GF3805@redhat.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Barracuda-Connect: mail1.int.fusionio.com[10.101.1.21] X-Barracuda-Start-Time: 1312269881 X-Barracuda-URL: http://10.101.1.180:8000/cgi-mod/mark.cgi X-Barracuda-Spam-Score: 0.00 X-Barracuda-Spam-Status: No, SCORE=0.00 using per-user scores of TAG_LEVEL=1000.0 QUARANTINE_LEVEL=1000.0 KILL_LEVEL=9.0 tests= X-Barracuda-Spam-Report: Code version 3.2, rules version 3.2.2.70668 Rule breakdown below pts rule name description ---- ---------------------- -------------------------------------------------- Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2011-08-01 20:47, Vivek Goyal wrote: > CFQ keeps track of number of groups which are linked on blkcg->blkg_list. > This is useful to avoid races between queue exit and cgroup exit code > paths. So if at the request queue exit time linked group count is not > zero, that means there are some group out there which is yet to be > deleted under rcu read period and queue exit code should wait for > on rcu period. > > In my previous patch I forgot to decrease the number of group count. > So in current form, we nr_blkcg_linked_grps is always non-zero and > we will always wait one rcu period (if BLK_CGROUP=y). The side effect > of this is that it can increase boot time. I am surprised, nobody > complained so far. Thanks Vivek, applied. -- Jens Axboe