From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CC174C433EF for ; Tue, 21 Sep 2021 11:18:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AEF9560EC0 for ; Tue, 21 Sep 2021 11:18:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232355AbhIULUB (ORCPT ); Tue, 21 Sep 2021 07:20:01 -0400 Received: from outbound-smtp33.blacknight.com ([81.17.249.66]:53731 "EHLO outbound-smtp33.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232270AbhIULT5 (ORCPT ); Tue, 21 Sep 2021 07:19:57 -0400 Received: from mail.blacknight.com (pemlinmail01.blacknight.ie [81.17.254.10]) by outbound-smtp33.blacknight.com (Postfix) with ESMTPS id 93B4F16C008 for ; Tue, 21 Sep 2021 12:18:18 +0100 (IST) Received: (qmail 30926 invoked from network); 21 Sep 2021 11:18:18 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.17.29]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 21 Sep 2021 11:18:18 -0000 Date: Tue, 21 Sep 2021 12:18:17 +0100 From: Mel Gorman To: dsterba@suse.cz, Matthew Wilcox , Linux-MM , NeilBrown , Theodore Ts'o , Andreas Dilger , "Darrick J . Wong" , Michal Hocko , Dave Chinner , Rik van Riel , Vlastimil Babka , Johannes Weiner , Jonathan Corbet , Linux-fsdevel , LKML Subject: Re: [RFC PATCH 0/5] Remove dependency on congestion_wait in mm/ Message-ID: <20210921111816.GS3959@techsingularity.net> References: <20210920085436.20939-1-mgorman@techsingularity.net> <20210920125058.GI3959@techsingularity.net> <20210920141152.GM9286@twin.jikos.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20210920141152.GM9286@twin.jikos.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 20, 2021 at 04:11:52PM +0200, David Sterba wrote: > On Mon, Sep 20, 2021 at 01:50:58PM +0100, Mel Gorman wrote: > > On Mon, Sep 20, 2021 at 12:42:44PM +0100, Matthew Wilcox wrote: > > > On Mon, Sep 20, 2021 at 09:54:31AM +0100, Mel Gorman wrote: > > > > This has been lightly tested only and the testing was useless as the > > > > relevant code was not executed. The workload configurations I had that > > > > used to trigger these corner cases no longer work (yey?) and I'll need > > > > to implement a new synthetic workload. If someone is aware of a realistic > > > > workload that forces reclaim activity to the point where reclaim stalls > > > > then kindly share the details. > > > > > > The stereeotypical "stalling on I/O" problem is to plug in one of the > > > crap USB drives you were given at a trade show and simply > > > dd if=/dev/zero of=/dev/sdb > > > sync > > > > > > > The test machines are 1500KM away so plugging in a USB stick but worst > > comes to the worst, I could test it on a laptop. > > There's a device mapper target dm-delay [1] that as it says delays the > reads and writes, so you could try to emulate the slow USB that way. > > [1] https://www.kernel.org/doc/html/latest/admin-guide/device-mapper/delay.html Ah, thanks for that tip. I wondered if something like this existed and clearly did not search hard enough. I was able to reproduce the problem without throttling but this could still be useful if examining cases where there are 2 or more BDIs with variable speeds. -- Mel Gorman SUSE Labs