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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 401CEC83F03 for ; Fri, 4 Jul 2025 07:03:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A08C46B8013; Fri, 4 Jul 2025 03:03:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9E04B6B800A; Fri, 4 Jul 2025 03:03:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 91DA06B8013; Fri, 4 Jul 2025 03:03:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 82AE46B800A for ; Fri, 4 Jul 2025 03:03:09 -0400 (EDT) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 76E47127676 for ; Fri, 4 Jul 2025 07:03:08 +0000 (UTC) X-FDA: 83625690456.12.EEF73A2 Received: from mail-ej1-f54.google.com (mail-ej1-f54.google.com [209.85.218.54]) by imf24.hostedemail.com (Postfix) with ESMTP id 5026E180008 for ; Fri, 4 Jul 2025 07:03:06 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=gmail.com header.s=20230601 header.b=iYjVQdAP; spf=pass (imf24.hostedemail.com: domain of kundanthebest@gmail.com designates 209.85.218.54 as permitted sender) smtp.mailfrom=kundanthebest@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1751612586; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=NaqZISU/6/J0dA6aXHHwQAgG0zenTBPemNnfGP8tRRw=; b=Spw6K23lBDdblTQtxQR5oYAPyc+LcXhF1ZauLtprOvVOqlV5qajbOXM+V1v6dRuo8+0hDJ BWl6UvZnW3dN/Zh0pYdKeLzaKE4cJHk/feZvmXRP2/Fp1Ta/W4/mWqFK7lYmwlH/hxxZiY n7qAXjdNfLC3oS5f3oGMRGXWH0B/2jg= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=gmail.com header.s=20230601 header.b=iYjVQdAP; spf=pass (imf24.hostedemail.com: domain of kundanthebest@gmail.com designates 209.85.218.54 as permitted sender) smtp.mailfrom=kundanthebest@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1751612586; a=rsa-sha256; cv=none; b=awXefi0kEtNHWIvZ44mPn42H73nrKovG6ujslNqAsZqg2CLKM67MG6Xjh53bqms4GjpZPr z/BojocPiXjD3X+x1iRIhRIhwk4oGQC9DM5Mo9NJXWsD4FjFgbeqCVRyqgXxVDUE3yODQN 75Qhj0O4OeM0bcplo3kBE17lwKAl2aw= Received: by mail-ej1-f54.google.com with SMTP id a640c23a62f3a-ade5b8aab41so126610066b.0 for ; Fri, 04 Jul 2025 00:03:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1751612585; x=1752217385; darn=kvack.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=NaqZISU/6/J0dA6aXHHwQAgG0zenTBPemNnfGP8tRRw=; b=iYjVQdAPtCl8KadPpE+Hp2AOvvWKrdTGTlChabkO0LcTh/ztiek4cC5oz9lI22ngcV 8YTWMX/75acCi77L7UT+3N0q1u6iwvIAio03khc5jDfUWrxwRYHmccI9szSukzB3KlkV +JsSJGhWSE3i8KmjhRGY583JqhkF3bBBo/te4AxDZhj00cnlNE3mkzttyP6xX7OWCAIj TN52z3c9zzpneZx3S9sq9Ul6kqbe56+bX8QBdj3vSxwhc1n6WnKeIJGlJ9G6m3qcBKQS MFNtqiVaAIk6YOpTPE5chCXJlNdG4xksaYaF5rbAWTDLRKtgjxUxzMYf1ORhoiYCG6M1 3gkA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1751612585; x=1752217385; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=NaqZISU/6/J0dA6aXHHwQAgG0zenTBPemNnfGP8tRRw=; b=aJlLf53OF8IabiMQDtvGePDx4r0rq+od0ztKKfkCokN4++5ndPwwNREomSCw/kWQpT wFuZCNSP1ZGdGlHYL1KlAtOkMo2Idv096YXUo4fq5uClK21Z25jnBSuZyHrUt+fgOauE IduGCTxHuT9IkdG/kT0HmMNXbS7/Ur/AIfglGHVqYPXNUHrEmVF80Ar+/OmbDOPrcySO WvPGmk8vpHohzs7h5v5/HlqZietPEfTP80eWEcuuGBLH85QCMLOfczXgNhsybl39t6sc e6hprj3zMFVwT+e8pVxROdDLuXo3uljNTTPic4eTBr+WBpHNMu1kwyZ0xyp1EcvO8xgN M3pg== X-Forwarded-Encrypted: i=1; AJvYcCVUx5o8v3SPkm3oZFmTysZ7FWoUnu2dZjVriEmoYQyj6Kcw3wivv7F4odvRmaAlDZc0N/TfQ/ugfA==@kvack.org X-Gm-Message-State: AOJu0Yx9Z2KvuioGyTTcHKYiy3X6OZStm95IzCb3K0vME8zhaOH74prf N3J5PW/3IFYH2jxWjKNLf9QllRZbeChX2wLQkmdcChYuAXYJiIAcfg5IxK9cxUK4+YeBjeamNZY eXjXCpW9/GjN90GLJKz9mZ1EjuiglJ4E= X-Gm-Gg: ASbGnctX8eBlozMQzoI5vPWxk5PHf9qaKKSqUD5ItbPBklDGrVJdqFeTt9x2+67Ktzp 3bVGKKTxcoqOsDR9g2iurPvvnwG/hNvTsbCvsQkaOxRERkYjNjehgLVTj977nXhPCNyu4azeBel avr6be8muQouN/Lu0LMWTqTEN2E0bEHJcMwnRtWXe+EHrHe0MkenNKDBgk+myQqz94LEG9Q3uzF QjQdOr8qAmOmyE2 X-Google-Smtp-Source: AGHT+IFH2+aa5C0AYTaAo7ldMEn47RrhFOI48HXYOTWtH8oGOiUW5l/So1Lz10mwcD0zFkQkk89KO90EiAPC2WiMYa4= X-Received: by 2002:a17:907:728e:b0:ae0:a813:1bc0 with SMTP id a640c23a62f3a-ae3fe78f7aemr85654066b.53.1751612584190; Fri, 04 Jul 2025 00:03:04 -0700 (PDT) MIME-Version: 1.0 References: <20250529111504.89912-1-kundan.kumar@samsung.com> <20250529203708.9afe27783b218ad2d2babb0c@linux-foundation.org> <20250702184312.GC9991@frogsfrogsfrogs> <20250703130500.GA23864@lst.de> In-Reply-To: <20250703130500.GA23864@lst.de> From: Kundan Kumar Date: Fri, 4 Jul 2025 12:32:51 +0530 X-Gm-Features: Ac12FXwZOjAgWNZaCPF5YBUk5PhxDjzykQsiKelmwtL0Fjc6XgS6xeUIPE87xdw Message-ID: Subject: Re: [PATCH 00/13] Parallelizing filesystem writeback To: Christoph Hellwig Cc: "Darrick J. Wong" , Andrew Morton , Kundan Kumar , jaegeuk@kernel.org, chao@kernel.org, viro@zeniv.linux.org.uk, Christian Brauner , jack@suse.cz, miklos@szeredi.hu, agruenba@redhat.com, Trond Myklebust , anna@kernel.org, Matthew Wilcox , mcgrof@kernel.org, clm@meta.com, david@fromorbit.com, amir73il@gmail.com, Jens Axboe , ritesh.list@gmail.com, dave@stgolabs.net, p.raghav@samsung.com, da.gomez@samsung.com, linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, gfs2@lists.linux.dev, linux-nfs@vger.kernel.org, linux-mm@kvack.org, gost.dev@samsung.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 5026E180008 X-Stat-Signature: up6zphhhxxdaqy9kzpozmtd1gfmxf8kk X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1751612586-75852 X-HE-Meta: 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 XqXeC+SA 8cU5+KWLC8G877ZYeYUh1LgYoSS4FVdWPPSYoUViuu4a+6aa6iQQngzON2i5KKjoAfWl/bdnLHAnBsyNRomgZGTEbdQEPeZKEKSEg5h8yokheHmaO89jU5qw24aRYjmwEH6gtCjaQQjn/4HsT+3LD0TOqQOLNchjLkIbdSr6YMW24kM8LdIf4c3thnIfVJ7OwmQ4ebCqMy9xkzWbcu6MmEB/9CKpwCAfM+rHOQtJpGQTBgFjO8XeW69VjmkhcaYY4LsQIiNO9x+UI6IFSywLUTPyL54PX3+Q8J/3AZNcMfq1osS0YcAO9VOBwrmFyI4GMMVzbwliDJ1T41MG/5Oce3AwVz8LjIUhCfUuRFinz8eSY3vb2lVmjqCNYu/j0oKcfOGppeErA3pbDwOb+4gbBKFQaA4suRgzYxRxEjOWAG9fT0TY= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jul 3, 2025 at 6:35=E2=80=AFPM Christoph Hellwig wrote= : > > On Wed, Jul 02, 2025 at 11:43:12AM -0700, Darrick J. Wong wrote: > > > On a spinning disk, random IO bandwidth remains unchanged, while sequ= ential > > > IO performance declines. However, setting nr_wb_ctx =3D 1 via configu= rable > > > writeback(planned in next version) eliminates the decline. > > > > > > echo 1 > /sys/class/bdi/8:16/nwritebacks > > > > > > We can fetch the device queue's rotational property and allocate BDI = with > > > nr_wb_ctx =3D 1 for rotational disks. Hope this is a viable solution = for > > > spinning disks? > > > > Sounds good to me, spinning rust isn't known for iops. > > > > Though: What about a raid0 of spinning rust? Do you see the same > > declines for sequential IO? > > Well, even for a raid0 multiple I/O streams will degrade performance > on a disk. Of course many real life workloads will have multiple > I/O streams anyway. > > I think the important part is to have: > > a) sane defaults > b) an easy way for the file system and/or user to override the default > > For a) a single thread for rotational is a good default. For file system > that driver multiple spindles independently or do compression multiple > threads might still make sense. > > For b) one big issue is that right now the whole writeback handling is > per-bdi and not per superblock. So maybe the first step needs to be > to move the writeback to the superblock instead of bdi? bdi is tied to the underlying block device, and helps for device bandwidth specific throttling, dirty ratelimiting etc. Making it per superblock will need duplicating the device specific throttling, ratelimiti= ng to superblock, which will be difficult. > If someone > uses partitions and multiple file systems on spinning rusts these > days reducing the number of writeback threads isn't really going to > save their day either. > in this case with single wb thread multiple partitions/filesystems use the same bdi, we fall back to base case, will that not help ?