From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-101.freemail.mail.aliyun.com (out30-101.freemail.mail.aliyun.com [115.124.30.101]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E23862690D5; Wed, 20 May 2026 11:38:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.101 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779277101; cv=none; b=V9W+rMtGskubpKK5wvorOYj7hJXVmC2xBiXLo5Z3MUufwqYcjnVYSNY/tRuCSteesLVRH+j9Dn3wcTiQBZCsAz2Cmrkw60EoIgXVkXI23jQPY9IbUGUtHhCWDT0bNQBsetVlI3fgXCZlrd3svtelim3MLr6nsmZDp20ZCp0BTI4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779277101; c=relaxed/simple; bh=gaZRzEzHOY2CfFs2vHkxu2ftNSrYHUb55zifcifZlck=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=sBrkBlxEV3f9dnbs+/KGXbyJsjqxgVTACXwGMO24WNKXbZbrCu7b2HqJcC6GYm7+xb7rtq9T/lYGrJU/WoQ2n7uwae3rPmA6qm02zmiUnBp03CmI7KakmEaXchZ6Q2CWIw5HaROlqx3n1fYHi60L84AuR9iELRdvh+ztQsVzCpI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=ri3/Rfi2; arc=none smtp.client-ip=115.124.30.101 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="ri3/Rfi2" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1779277095; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=ub71hIbpe3G2zjp/ezNUEfE96sZBOZFBfh43PEc2oV0=; b=ri3/Rfi2kZDiWCV1IOaKHrBdZtvbN5TR1ncPlhrmEGyqY19IAABq5/jfPHEBlGNI7lEnQdigQ0toGG/P+PX/kwfSylITO6VBF2vhwUC8t6YX2ImGkZxoJke0SPUc/Dwx9ZP9f523DJm/PuDeL9+sHiGZrTlQHcRnK9sOdnxIuMw= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037009110;MF=libaokun@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0X3Iu716_1779277093; Received: from 30.221.129.237(mailfrom:libaokun@linux.alibaba.com fp:SMTPD_---0X3Iu716_1779277093 cluster:ay36) by smtp.aliyun-inc.com; Wed, 20 May 2026 19:38:14 +0800 Message-ID: Date: Wed, 20 May 2026 19:38:12 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/3] writeback: drop now-unnecessary rcu_barrier() in cgroup_writeback_umount() To: Jan Kara Cc: linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, tj@kernel.org, linux-kernel@vger.kernel.org References: <20260518135349.1187628-1-libaokun@linux.alibaba.com> <20260518135349.1187628-3-libaokun@linux.alibaba.com> From: Baokun Li In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 2026/5/20 16:46, Jan Kara wrote: > On Mon 18-05-26 21:53:48, Baokun Li wrote: >> Commit e1b849cfa6b6 ("writeback: Avoid contention on wb->list_lock when >> switching inodes") replaced the queue_rcu_work() based scheduling of >> inode wb switches with a plain queue_work(). Since then no switcher >> goes through call_rcu(), so rcu_barrier() in cgroup_writeback_umount() >> has no callbacks of its own to wait for. It still drains unrelated >> call_rcu() callbacks from other subsystems on busy systems, which >> incidentally slows umount down; drop it. >> >> Fixes: e1b849cfa6b6 ("writeback: Avoid contention on wb->list_lock when switching inodes") >> Signed-off-by: Baokun Li > I've already replied to previous version but anyway: feel free to add: > > Reviewed-by: Jan Kara > > Honza Hi Honza, Thank you for your review! Sorry for the rushed v3 — your Reviewed-by on v2 came in right after I hit send, so I missed picking it up. I'll carry it forward in v4. Thanks, Baokun >> --- >> fs/fs-writeback.c | 5 ----- >> 1 file changed, 5 deletions(-) >> >> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c >> index 6766de9f9d75..325a30cc35bf 100644 >> --- a/fs/fs-writeback.c >> +++ b/fs/fs-writeback.c >> @@ -1248,11 +1248,6 @@ void cgroup_writeback_umount(struct super_block *sb) >> * will then drain it. >> */ >> synchronize_rcu(); >> - /* >> - * Use rcu_barrier() to wait for all pending callbacks to >> - * ensure that all in-flight wb switches are in the workqueue. >> - */ >> - rcu_barrier(); >> flush_workqueue(isw_wq); >> } >> } >> -- >> 2.43.7 >>