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Fri, 21 Aug 2026 12:08:44 +0000 (GMT) Message-ID: <5f212467-8920-4273-aa01-29d80d6e8f6a@samsung.com> Date: Fri, 21 Aug 2026 17:38:43 +0530 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 4/6] xfs: generic AG set based steering To: Christoph Hellwig Cc: brauner@kernel.org, djwong@kernel.org, dgc@kernel.org, jack@suse.cz, cem@kernel.org, axboe@kernel.dk, kbusch@kernel.org, ritesh.list@gmail.com, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, gost.dev@samsung.com, Anuj Gupta Content-Language: en-US From: Kanchan Joshi In-Reply-To: <20260819072137.GG1541@lst.de> Content-Transfer-Encoding: 7bit X-CMS-MailID: 20260821120846epcas5p1a48ba61937cb24bd471b1c9513285c0d X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" CMS-TYPE: 105P cpgsPolicy: CPGSC10-542,Y X-CFilter-Loop: Reflected X-CMS-RootMailID: 20260717125636epcas5p2b68dd498717813e0b395b9d57d9d97df References: <20260717125538.508925-1-joshi.k@samsung.com> <20260717125538.508925-5-joshi.k@samsung.com> <20260819072137.GG1541@lst.de> On 8/19/2026 12:51 PM, Christoph Hellwig wrote: > On Fri, Jul 17, 2026 at 06:25:36PM +0530, Kanchan Joshi wrote: >> Improve allocator concurrency and reduce interleaving by introducing >> fixed sized AG set. >> Use low bits of the inode as a hash to select AG within the AG set. >> Overall, a file will try to use the same AG (and contiguity is maintained), >> but multiple files will be spread across all AGs in the target AG set. > I'm a bit worried this kind of magic - the inodes close to each other > might not all have data or very different amounts of data. > > I suspect the root cause this helps with is that the XFS initial data > placement algorithm that tries to place file data next to the inode is > actively harmful these days. So doing an initial AG selection similar > to how the RT device does the initial RTG selection might be more > useful here (and thinking about moving to an inode32-like scheme > where small metadata with a lot of churn is constrained to a few > AGs). Thinking to drop this for now, as this may need a distinct series. This patch was here because stream based AG-set extended what this patch was doing (i.e., the minimal fixed-size AG-set). That relationship goes with the change you mentioned. Replacing default AG allocator with an automatic RG-style rotor (no user-supplied write-stream) might be a radical change in terms of impact.