From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 50F8C35C6AF; Tue, 29 Sep 2026 22:09:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790719771; cv=none; b=KTp2zTeZjRi4l2wAR5oQ5FYGqUK8szsIZ1QqJryuY9c/7B05DKw/6KjcNp0JZJX+Kr6jqOEYCoyCMSu0a6MXaLzYqby/3bGULj2mllvfa5j55tVGz8oikffVZgfLGiHKcDKtCLaML7do4n6/gCXzuSPJ3Q3qf60FEybt51/rqF8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790719771; c=relaxed/simple; bh=qCrSFVQz80ym8Oq/bHs94zgjAS/ZMdvhcxJmm22/tNo=; h=Date:To:From:Subject:Message-Id; b=cRZf2wgDDN8tLpYyo5zcuxfCm3VPC5LipZ1WkZIxDJZE7z62M58CMhTajFBt6xXowoxWtXG13P84iy4gyHfgIuODVbQWT8UcIATO7JR9tLUljr/HMrzBbjV6XzHaSyYPZWkympM6/pwWEveYZqHir+3bBErtMzKovPxAt3z3SsU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=t6FBDaV2; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="t6FBDaV2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D7B281F000FF; Tue, 29 Sep 2026 22:09:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1790719770; bh=lNh2BGGBmKhZABxsUsrPWXLMJYnXvWBTllVrkNMR88M=; h=Date:To:From:Subject; b=t6FBDaV2wvbJ1Y9ldgROnsZWMkRoN9GIl1jfZNCApeJi9AVdNqaWm3dcRaJWnQX23 1rGVXZFqZKPQU4IC1jUpjfrgrt1ggWF4ASWbpM3AR4bsbClBn4gequ29zE9DLR+mLB i/m28UfaxeG7kOMFQKocGfY3UHe53qeWNDiTdHKE= Date: Tue, 29 Sep 2026 15:09:29 -0700 To: mm-commits@vger.kernel.org,willy@infradead.org,viro@zeniv.linux.org.uk,tj@kernel.org,stable@vger.kernel.org,roman.gushchin@linux.dev,jack@suse.cz,dennis@kernel.org,brauner@kernel.org,perf.patrick.lu@gmail.com,akpm@linux-foundation.org From: Andrew Morton Subject: [merged] writeback-bound-cleanup_offline_cgwb-rescans-by-rotating-scanned-inodes.patch removed from -mm tree Message-Id: <20260929220929.D7B281F000FF@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: writeback: bound cleanup_offline_cgwb() rescans by rotating scanned inodes has been removed from the -mm tree. Its filename was writeback-bound-cleanup_offline_cgwb-rescans-by-rotating-scanned-inodes.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: "Patrick Lu (Anthropic)" Subject: writeback: bound cleanup_offline_cgwb() rescans by rotating scanned inodes Date: Fri, 11 Sep 2026 18:49:49 +0000 cleanup_offline_cgwb() prepares at most WB_MAX_INODES_PER_ISW inodes per call and is called again until the dying wb is drained, but every call walks wb->b_attached and then wb->b_dirty_time from the same end. Inodes already prepared (they stay on the list with I_WB_SWITCH set until the switch worker runs) and inodes that cannot be switched (I_FREEING, I_WILL_FREE, !SB_ACTIVE, DAX, already on the target wb) stay where they are, so each pass rescans a growing run of them under wb->list_lock and a full drain is quadratic in the number of inodes on the list. With ~17M inodes attached to one dying cgwb we saw this end in soft lockups, with CPUs reported stuck for 21-48s. Walk both lists from the oldest end and move every scanned inode to the newest end, so the next pass starts where the previous one stopped and the drain becomes linear. b_attached is unordered, so nobody sees the reorder there. b_dirty_time is ordered by dirtied_when, but the oldest unscanned inode stays at the end move_expired_inodes() picks from, sync takes the whole list regardless of order, and prepared inodes leave the list as soon as the switch work runs and get a new dirtied_time_when on the new wb anyway, so the only inodes left out of order are the ones that can never switch (DAX), and only on the dying wb. Seen in production on a 6.18-based kernel: with ~17M inodes attached to one dying cgwb, a node spent 36 minutes in back-to-back wb->list_lock holds by the cleanup scanner (~6ms each, ~46% of wall time, starving writeback on that wb); with v1 of this patch the same workload drains in ~30 seconds. Also seen on stock Amazon Linux 2023 6.12.68 as isw workers spinning on the list_lock in inode_switch_wbs_work_fn() while cleanup_offline_cgwbs_workfn() runs. Link: https://lore.kernel.org/20260911-wb-cgwb-rotate-v2-1-a9ab253a1295@gmail.com Fixes: c22d70a162d3 ("writeback, cgroup: release dying cgwbs by switching attached inodes") Signed-off-by: Patrick Lu (Anthropic) Signed-off-by: Andrew Morton Acked-by: Tejun Heo Acked-by: Roman Gushchin Reviewed-by: Jan Kara Assisted-by: LLM Cc: Al Viro Cc: Christian Brauner Cc: Dennis Zhou Cc: Matthew Wilcox (Oracle) Cc: --- fs/fs-writeback.c | 25 ++++++++++++++++++++----- 1 file changed, 20 insertions(+), 5 deletions(-) --- a/fs/fs-writeback.c~writeback-bound-cleanup_offline_cgwb-rescans-by-rotating-scanned-inodes +++ a/fs/fs-writeback.c @@ -727,19 +727,34 @@ static bool isw_prepare_wbs_switch(struc struct inode_switch_wbs_context *isw, struct list_head *list, int *nr) { - struct inode *inode; + struct inode *inode, *tmp; + LIST_HEAD(scanned); + bool full = false; + + /* + * Walk from the oldest end and move scanned inodes to the newest + * end, so the next scan resumes at unscanned inodes instead of + * re-walking an ever-growing run of prepared and skipped ones. + * For b_dirty_time this keeps the oldest unscanned inode at the + * end move_expired_inodes() picks from; b_attached is unordered. + */ + list_for_each_entry_safe_reverse(inode, tmp, list, i_io_list) { + list_move(&inode->i_io_list, &scanned); - list_for_each_entry(inode, list, i_io_list) { if (!inode_prepare_wbs_switch(inode, new_wb)) continue; isw->inodes[*nr] = inode; (*nr)++; - if (*nr >= WB_MAX_INODES_PER_ISW - 1) - return true; + if (*nr >= WB_MAX_INODES_PER_ISW - 1) { + full = true; + break; + } } - return false; + list_splice(&scanned, list); + + return full; } /** _ Patches currently in -mm which might be from perf.patrick.lu@gmail.com are