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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tvGvL-0000000BzxE-2fcV; Thu, 20 Mar 2025 14:31:07 +0000 Date: Thu, 20 Mar 2025 14:31:07 +0000 From: Matthew Wilcox To: Daniel Gomez Cc: Luis Chamberlain , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, lsf-pc@lists.linux-foundation.org, david@fromorbit.com, leon@kernel.org, hch@lst.de, kbusch@kernel.org, sagi@grimberg.me, axboe@kernel.dk, joro@8bytes.org, brauner@kernel.org, hare@suse.de, djwong@kernel.org, john.g.garry@oracle.com, ritesh.list@gmail.com, p.raghav@samsung.com, gost.dev@samsung.com, da.gomez@samsung.com Subject: Re: [LSF/MM/BPF TOPIC] breaking the 512 KiB IO boundary on x86_64 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 6F1BF10003A X-Rspamd-Server: rspam05 X-Stat-Signature: s9hnbfpww1ndeude8bh3yg8p47qf1djb X-HE-Tag: 1742481073-261228 X-HE-Meta: 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 7NqNO3uF E4CNjrIQxpibgd5GjNNP+hKMFElpP4n50/cP6Zg2YhM/5gC+RxUX2DGUDoGzFQnbq4K9y6iVkw+QS3dsNEMaXbqMbrrcUefspMMKx2Osr321HeUfmMOGaJpG6ZuLiS+e92ZUZL3ggGNB7LE4P7v1VxisvOTOQDQnKn4ye6QW+38I7NRA2efL7kkyIr/LZDgjkz3WSAbPUtuWtq0BfJ3mX93oyDey11lF30kHbgmbK8OZOr5V68JXv7AYtH74L5miHsbAiJMx8uW5CkPSQGaQHHFY4wxeDJDcEz4xx/gOZQLDjKdnSI79U3BW+8smZtXmuCCe9woplkFvLxQ8vGksU1odZNKw9wsRHNIKRUB0LAMPH/rIm/cbPiY/pIw== 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, Mar 20, 2025 at 02:29:56PM +0100, Daniel Gomez wrote: > On Thu, Mar 20, 2025 at 12:11:47PM +0100, Matthew Wilcox wrote: > > On Thu, Mar 20, 2025 at 04:41:11AM -0700, Luis Chamberlain wrote: > > > We've been constrained to a max single 512 KiB IO for a while now on x86_64. > > ... > > > It does beg a few questions: > > > > > > - How are we computing the new max single IO anyway? Are we really > > > bounded only by what devices support? > > > - Do we believe this is the step in the right direction? > > > - Is 2 MiB a sensible max block sector size limit for the next few years? > > > - What other considerations should we have? > > > - Do we want something more deterministic for large folios for direct IO? > > > > Is the 512KiB limit one that real programs actually hit? Would we > > see any benefit from increasing it? A high end NVMe device has a > > bandwidth limit around 10GB/s, so that's reached around 20k IOPS, > > which is almost laughably low. > > Current devices do more than that. A quick search gives me 14GB/s and 2.5M IOPS > for gen5 devices: > > https://semiconductor.samsung.com/ssd/enterprise-ssd/pm1743/ > > An gen6 goes even further. That kind of misses my point. You don't need to exceed 512KiB I/Os to be bandwidth limited. So what's the ROI of all this work? Who benefits?