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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 52B79C433FE for ; Fri, 4 Mar 2022 00:43:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234460AbiCDAnv (ORCPT ); Thu, 3 Mar 2022 19:43:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38198 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232482AbiCDAnv (ORCPT ); Thu, 3 Mar 2022 19:43:51 -0500 Received: from lgeamrelo11.lge.com (lgeamrelo12.lge.com [156.147.23.52]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 49C834926C for ; Thu, 3 Mar 2022 16:43:01 -0800 (PST) Received: from unknown (HELO lgeamrelo02.lge.com) (156.147.1.126) by 156.147.23.52 with ESMTP; 4 Mar 2022 09:42:59 +0900 X-Original-SENDERIP: 156.147.1.126 X-Original-MAILFROM: byungchul.park@lge.com Received: from unknown (HELO X58A-UD3R) (10.177.244.38) by 156.147.1.126 with ESMTP; 4 Mar 2022 09:42:59 +0900 X-Original-SENDERIP: 10.177.244.38 X-Original-MAILFROM: byungchul.park@lge.com Date: Fri, 4 Mar 2022 09:42:37 +0900 From: Byungchul Park To: Theodore Ts'o Cc: damien.lemoal@opensource.wdc.com, linux-ide@vger.kernel.org, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, torvalds@linux-foundation.org, mingo@redhat.com, linux-kernel@vger.kernel.org, peterz@infradead.org, will@kernel.org, tglx@linutronix.de, rostedt@goodmis.org, joel@joelfernandes.org, sashal@kernel.org, daniel.vetter@ffwll.ch, chris@chris-wilson.co.uk, duyuyang@gmail.com, johannes.berg@intel.com, tj@kernel.org, willy@infradead.org, david@fromorbit.com, amir73il@gmail.com, bfields@fieldses.org, gregkh@linuxfoundation.org, kernel-team@lge.com, linux-mm@kvack.org, akpm@linux-foundation.org, mhocko@kernel.org, minchan@kernel.org, hannes@cmpxchg.org, vdavydov.dev@gmail.com, sj@kernel.org, jglisse@redhat.com, dennis@kernel.org, cl@linux.com, penberg@kernel.org, rientjes@google.com, vbabka@suse.cz, ngupta@vflare.org, linux-block@vger.kernel.org, paolo.valente@linaro.org, josef@toxicpanda.com, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, jack@suse.cz, jack@suse.com, jlayton@kernel.org, dan.j.williams@intel.com, hch@infradead.org, djwong@kernel.org, dri-devel@lists.freedesktop.org, airlied@linux.ie, rodrigosiqueiramelo@gmail.com, melissa.srw@gmail.com, hamohammed.sa@gmail.com Subject: Re: Report 2 in ext4 and journal based on v5.17-rc1 Message-ID: <20220304004237.GB6112@X58A-UD3R> References: <1646285013-3934-1-git-send-email-byungchul.park@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Mar 03, 2022 at 09:36:25AM -0500, Theodore Ts'o wrote: > On Thu, Mar 03, 2022 at 02:23:33PM +0900, Byungchul Park wrote: > > I totally agree with you. *They aren't really locks but it's just waits > > and wakeups.* That's exactly why I decided to develop Dept. Dept is not > > interested in locks unlike Lockdep, but fouces on waits and wakeup > > sources itself. I think you get Dept wrong a lot. Please ask me more if > > you have things you doubt about Dept. > > So the question is this --- do you now understand why, even though > there is a circular dependency, nothing gets stalled in the > interactions between the two wait channels? ??? I'm afraid I don't get you. All contexts waiting for any of the events in the circular dependency chain will be definitely stuck if there is a circular dependency as I explained. So we need another wakeup source to break the circle. In ext4 code, you might have the wakeup source for breaking the circle. What I agreed with is: The case that 1) the circular dependency is unevitable 2) there are another wakeup source for breadking the circle and 3) the duration in sleep is short enough, should be acceptable. Sounds good? Thanks, Byungchul