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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9CFBDCCFA05 for ; Fri, 7 Nov 2025 13:37:51 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C010B8E0009; Fri, 7 Nov 2025 08:37:50 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id BD84D8E0002; Fri, 7 Nov 2025 08:37:50 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B15908E0009; Fri, 7 Nov 2025 08:37:50 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 9FF198E0002 for ; Fri, 7 Nov 2025 08:37:50 -0500 (EST) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 6C4944B9BE for ; Fri, 7 Nov 2025 13:37:50 +0000 (UTC) X-FDA: 84083913900.26.A3AFD91 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by imf16.hostedemail.com (Postfix) with ESMTP id 90A52180010 for ; Fri, 7 Nov 2025 13:37:48 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=none; spf=pass (imf16.hostedemail.com: domain of hch@lst.de designates 213.95.11.211 as permitted sender) smtp.mailfrom=hch@lst.de; dmarc=pass (policy=none) header.from=lst.de ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1762522668; 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: in-reply-to:in-reply-to:references:references; bh=4fW4ByonwXrt8CCQV5evrDbXfC526l8bUSvhPi4LoTk=; b=NNdXeWnoR9kPBPSAA/ZCdsl5bxsnTQhkOwoUYzrvgWFEO4NgwGtb01OHiOyvgK/I0EGirU h4OhrRxKKponzgr0P8+vPagVML1WTWol/mhBXt9FjvYblCrXmS4kljzTlbD7KTxQ/Uwr6F 1RSkbgabeAAtJgIXbB6XULWJLuBMmzQ= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=none; spf=pass (imf16.hostedemail.com: domain of hch@lst.de designates 213.95.11.211 as permitted sender) smtp.mailfrom=hch@lst.de; dmarc=pass (policy=none) header.from=lst.de ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1762522668; a=rsa-sha256; cv=none; b=higOLwgXG6AnUNMy3Hl0bw0Wqez6M+uD5AgcKZpIoJk9dfC74MRiDi0sbZ4CqIFjQTVXeJ 8B/2xCNcX+pe/BiwHoJiFb1JHgR54+Zo6DlEo6kjwiEq4sdEt36qc8RduRxG4ChYULyaYq +lRLQQOeXA4Ej8BLzBZPXf2/pAIXVQs= Received: by verein.lst.de (Postfix, from userid 2407) id 6E374227AAE; Fri, 7 Nov 2025 14:37:42 +0100 (CET) Date: Fri, 7 Nov 2025 14:37:42 +0100 From: Christoph Hellwig To: Kundan Kumar Cc: Christoph Hellwig , "Darrick J. Wong" , Dave Chinner , jaegeuk@kernel.org, chao@kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, miklos@szeredi.hu, agruenba@redhat.com, trondmy@kernel.org, anna@kernel.org, akpm@linux-foundation.org, willy@infradead.org, mcgrof@kernel.org, clm@meta.com, amir73il@gmail.com, axboe@kernel.dk, ritesh.list@gmail.com, dave@stgolabs.net, wangyufei@vivo.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, anuj20.g@samsung.com, vishak.g@samsung.com, joshi.k@samsung.com Subject: Re: [PATCH v2 00/16] Parallelizing filesystem writeback Message-ID: <20251107133742.GA5596@lst.de> References: <20251014120845.2361-1-kundan.kumar@samsung.com> <20251022043930.GC2371@lst.de> <20251029060932.GS4015566@frogsfrogsfrogs> <20251029085526.GA32407@lst.de> <91367b76-e48b-46b4-b10b-43dfdd8472fa@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <91367b76-e48b-46b4-b10b-43dfdd8472fa@samsung.com> User-Agent: Mutt/1.5.17 (2007-11-01) X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 90A52180010 X-Stat-Signature: 8zj5sz4hpxnxe1omxa811g1ooh7mipdn X-Rspam-User: X-HE-Tag: 1762522668-416296 X-HE-Meta: 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 SDv37hCv 6GMuc/csK9/3c5V/nnbCE4HUr57eF+F56tLrl7uOIji6pHFvzDnTKAhu9ijdL7Uj81oP+BjMyY94CCi+0u/91OmiLELDwnn8InQNT4gOz/f8oUJ5GqKSLf2SA8NDC0YxU2RswCPxm3TEREqwPnCHi5RLssPU+Xwl+V3D0vRvyatogVl4= 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 Fri, Nov 07, 2025 at 02:54:42PM +0530, Kundan Kumar wrote: > Predicting the Allocation Group (AG) for aged filesystems and passing > this information to per-AG writeback threads appears to be a complex > task. Yes. But in the end aged file systems are what will see most usage. Fresh file systems look nice in benchmarks, but they aren't what users will mostly deal with. > To segregate these I/O requests by AG, it is necessary to associate > AG-specific information with the pages/folios in the page cache. Two > possible approaches are: > (1) storing AG information in the folio->private field, or > (2) introducing new markers in the xarray to track AG-specific data. > > The AG-affined writeback thread processes specific pages from the page > cache marked for its AG. Is this a viable approach, or are there > alternative solutions that could be more effective? Or maybe the per-AG scheme isn't that great after all and we just need some other simple sharding scheme? Of course lock contention will be nicer on a per-AG basis, but as you found out actually mapping high-level writeback to AGs is pretty hard.