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 4932EC77B73 for ; Sun, 30 Apr 2023 04:50:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230114AbjD3EkP (ORCPT ); Sun, 30 Apr 2023 00:40:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48338 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229452AbjD3EkO (ORCPT ); Sun, 30 Apr 2023 00:40:14 -0400 Received: from out28-65.mail.aliyun.com (out28-65.mail.aliyun.com [115.124.28.65]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6C4BFE7C; Sat, 29 Apr 2023 21:40:10 -0700 (PDT) X-Alimail-AntiSpam: AC=CONTINUE;BC=0.04437546|-1;CH=green;DM=|CONTINUE|false|;DS=CONTINUE|ham_regular_dialog|0.00842704-0.000887824-0.990685;FP=0|0|0|0|0|-1|-1|-1;HT=ay29a033018047205;MF=wangyugui@e16-tech.com;NM=1;PH=DS;RN=8;RT=8;SR=0;TI=SMTPD_---.SUWc2Yx_1682829606; Received: from 192.168.2.112(mailfrom:wangyugui@e16-tech.com fp:SMTPD_---.SUWc2Yx_1682829606) by smtp.aliyun-inc.com; Sun, 30 Apr 2023 12:40:07 +0800 Date: Sun, 30 Apr 2023 12:40:08 +0800 From: Wang Yugui To: Tejun Heo Subject: Re: [PATCH 16/22] btrfs: Use alloc_ordered_workqueue() to create ordered workqueues Cc: jiangshanlai@gmail.com, linux-kernel@vger.kernel.org, kernel-team@meta.com, Chris Mason , Josef Bacik , David Sterba , linux-btrfs@vger.kernel.org In-Reply-To: <20230421025046.4008499-17-tj@kernel.org> References: <20230421025046.4008499-1-tj@kernel.org> <20230421025046.4008499-17-tj@kernel.org> Message-Id: <20230430124006.49D2.409509F4@e16-tech.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.81.04 [en] Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Hi, > BACKGROUND > ========== > > When multiple work items are queued to a workqueue, their execution order > doesn't match the queueing order. They may get executed in any order and > simultaneously. When fully serialized execution - one by one in the queueing > order - is needed, an ordered workqueue should be used which can be created > with alloc_ordered_workqueue(). > > However, alloc_ordered_workqueue() was a later addition. Before it, an > ordered workqueue could be obtained by creating an UNBOUND workqueue with > @max_active==1. This originally was an implementation side-effect which was > broken by 4c16bd327c74 ("workqueue: restore WQ_UNBOUND/max_active==1 to be > ordered"). Because there were users that depended on the ordered execution, > 5c0338c68706 ("workqueue: restore WQ_UNBOUND/max_active==1 to be ordered") > made workqueue allocation path to implicitly promote UNBOUND workqueues w/ > @max_active==1 to ordered workqueues. > > While this has worked okay, overloading the UNBOUND allocation interface > this way creates other issues. It's difficult to tell whether a given > workqueue actually needs to be ordered and users that legitimately want a > min concurrency level wq unexpectedly gets an ordered one instead. With > planned UNBOUND workqueue updates to improve execution locality and more > prevalence of chiplet designs which can benefit from such improvements, this > isn't a state we wanna be in forever. > > This patch series audits all callsites that create an UNBOUND workqueue w/ > @max_active==1 and converts them to alloc_ordered_workqueue() as necessary. > > WHAT TO LOOK FOR > ================ > > The conversions are from > > alloc_workqueue(WQ_UNBOUND | flags, 1, args..) > > to > > alloc_ordered_workqueue(flags, args...) > > which don't cause any functional changes. If you know that fully ordered > execution is not ncessary, please let me know. I'll drop the conversion and > instead add a comment noting the fact to reduce confusion while conversion > is in progress. > > If you aren't fully sure, it's completely fine to let the conversion > through. The behavior will stay exactly the same and we can always > reconsider later. > > As there are follow-up workqueue core changes, I'd really appreciate if the > patch can be routed through the workqueue tree w/ your acks. Thanks. Should we add alloc_ordered_workqueue to btrfs_alloc_workqueue() of fs/btrfs/async-thread.c too? Best Regards Wang Yugui (wangyugui@e16-tech.com) 2023/04/30 > > Signed-off-by: Tejun Heo > Cc: Chris Mason > Cc: Josef Bacik > Cc: David Sterba > Cc: linux-btrfs@vger.kernel.org > --- > fs/btrfs/disk-io.c | 2 +- > fs/btrfs/scrub.c | 6 ++++-- > 2 files changed, 5 insertions(+), 3 deletions(-) > > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c > index 9e1596bb208d..b1f6ff69dbe1 100644 > --- a/fs/btrfs/disk-io.c > +++ b/fs/btrfs/disk-io.c > @@ -2218,7 +2218,7 @@ static int btrfs_init_workqueues(struct btrfs_fs_info *fs_info) > fs_info->qgroup_rescan_workers = > btrfs_alloc_workqueue(fs_info, "qgroup-rescan", flags, 1, 0); > fs_info->discard_ctl.discard_workers = > - alloc_workqueue("btrfs_discard", WQ_UNBOUND | WQ_FREEZABLE, 1); > + alloc_ordered_workqueue("btrfs_discard", WQ_FREEZABLE); > > if (!(fs_info->workers && fs_info->hipri_workers && > fs_info->delalloc_workers && fs_info->flush_workers && > diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c > index 69c93ae333f6..70882358bdb0 100644 > --- a/fs/btrfs/scrub.c > +++ b/fs/btrfs/scrub.c > @@ -4245,8 +4245,10 @@ static noinline_for_stack int scrub_workers_get(struct btrfs_fs_info *fs_info, > if (refcount_inc_not_zero(&fs_info->scrub_workers_refcnt)) > return 0; > > - scrub_workers = alloc_workqueue("btrfs-scrub", flags, > - is_dev_replace ? 1 : max_active); > + if (is_dev_replace) > + scrub_workers = alloc_ordered_workqueue("btrfs-scrub", flags); > + else > + scrub_workers = alloc_workqueue("btrfs-scrub", flags, max_active); > if (!scrub_workers) > goto fail_scrub_workers; > > -- > 2.40.0