From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=82.195.75.108 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793980130; b=WccDm4RfrfXNyXMG2tB+PPkFwZs8+0XNpzfzFHuakieEWiJeycHWmsXFNQ7YrMJGYwjs bftG3jvOPulpRmQhAVEy9MT5rch899LkWfaE1ZiCRRTb9G1orYKIaKa9lkGcRJUCJyIY+ wEP8MKYxivrz9iqRO6BFkilW1N1wtCVjkn2UxVon7QArpcOsmSA8MvlrarjD2JYdJSYA+ q08vo+R8+UNTI7GeNGQvUkSkl7ou71vVKZ54cZT1JIpgem/LvXjeAyBPnhk3fwMBxjoPN 3z63hBEyQTFADsYf2ZDvni8kRBhtHwYQXC+7OXNe+qiahN5A6gTvI6Sec6nTnNfV3oQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793980130; h=DMARC-Filter:DKIM-Signature:Received:Date:From:To:Cc:Subject: Message-ID:References:MIME-Version:Content-Type:Content-Disposition: In-Reply-To:X-Debian-User; bh=tYP5TleIEch3VLAIP9Ft5HxHg1kcwlIJDfJyqYRyetQ=; b=rriQpzxsgdH3T8fLlFNrVYp0zxsmktSV7HH5Lp/4ziOKPqKICyJVyJVfdRgCS+dlQ5yc reQ/+OTsQOCkMcWl1yQ5aDlQxzF3mOKOkbk8fc/VchFtaVym0Qmj6ayuyo+ReW1TpGZdA rCPHJ8qpRbroXVTYHZJi6fgr5PXbtG0UZracdJosyUdx45BIHWjrPfKiJb3Mr6YVkCwoC qodPSy3T6qyQW58eqskQ6P0hp6qDJyzvKbI0d1nIQNyA+91JBoJD1FeX1z4nv6g4JFlWf +cIkn7omx9fixbUreCs/8GhHEg8FbcctkekhPh3JLp/eVIVGkjpljvkmDBUg1iaUn9w== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=debian.org; spf=pass smtp.mailfrom=debian.org; dkim=pass header.d=debian.org header.i=@debian.org header.a=rsa-sha256 header.s=smtpauto.stravinsky header.b=kawekjpF; arc=none smtp.remote-ip=82.195.75.108 Received: from stravinsky.debian.org (stravinsky.debian.org [82.195.75.108]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (prime256v1) server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0F238606A326; Fri, 6 Nov 2026 15:48:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 0F238606A326 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=debian.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=debian.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=debian.org header.i=@debian.org header.a=rsa-sha256 header.s=smtpauto.stravinsky header.b=kawekjpF DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=debian.org; s=smtpauto.stravinsky; h=X-Debian-User:In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=tYP5TleIEch3VLAIP9Ft5HxHg1kcwlIJDfJyqYRyetQ=; b=kawekjpFkeEGdTL/oDhrDnFvls K1D01E+FexEpQanMibxBalmMtyOvnUTJ+UVQ8QxUMrKmFHlioowyeYzLKNbVsfgIp7VObIcFExEpf vqYossnW/QB+XhOiQZEppddiMVHXWse+H6IqywSELZUSdLbBdVk4mDFaLTGnjY6c1zXFYdGRZviu1 a1JRUdlohP6HrX1J+E2nkajmSx1GeiVHJV/RkCNrWDiGtvZFHB+MgKikLbDD8f/s+7y4Wh1Uqfyl8 3xiLyWiCoerUT2LoIv1B8UEwXKqw9UuoY2k0ksG4hzsmmN4H47F7SWp6jznWjd8iBPUPCXWoA9lv+ luXUpRbA==; Received: from authenticated-user by stravinsky.debian.org with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.96) (envelope-from ) id 1xPMBA-009OCi-2T; Fri, 06 Nov 2026 15:48:37 +0000 Date: Fri, 6 Nov 2026 07:48:30 -0800 From: Breno Leitao To: Jan Kara Cc: Alexander Viro , Christian Brauner , Julian Sun , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Johannes Weiner , Roman Gushchin , Shakeel Butt , Muchun Song , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH 2/4] writeback: name the bdi in the slow writeback report Message-ID: References: <20261106-writeback_stall_report-v1-0-bf0c3b9023a5@debian.org> <20261106-writeback_stall_report-v1-2-bf0c3b9023a5@debian.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Debian-User: leitao On Fri, Nov 06, 2026 at 03:27:49PM +0100, Jan Kara wrote: > On Fri 06-11-26 04:26:32, Breno Leitao wrote: > > The slow writeback report names the waiting task and how long it has > > waited, but not what it is waiting on. On a machine with several > > filesystems there is no way to tell which device is slow. > > > > Pass the bdi to wb_wait_for_completion() and print its name on a second > > line, together with the number of work items still outstanding. A sync > > issues one work item per cgroup wb with dirty inodes, so the count also > > shows whether a single cgroup is holding up the others. > > > > wb_wait_for_completion() took the bdi until commit 5b9cce4c7eb0 > > ("writeback: Generalize and expose wb_completion") made it usable for > > the memcg foreign flushes. memcg tracks those by bdi id only and passes > > NULL, which bdi_dev_name() prints as "(unknown)". > > > > The first line does not change, so anything matching on it keeps > > working. A sync on a throttled null_blk device now reports: > > > > INFO: The task sync:180 has been waiting for writeback completion for more than 28 seconds. > > bdi 252:0, work items left: 1 > > > > Signed-off-by: Breno Leitao > > Dunno, I'd put everything on one line. Otherwise things can get interleaved > by other messages. Kernel messages are not really an ABI, we can change > them... Ack! I will get them in a single line and respin, --breno