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b=coADCjkKky5l1VpWZZMoqTmplW8HxyaN3yHoTHbGRo+idKiZY7UyLEm/qzPgl5qIU WVc1o2FKrtvtCnYF5oOC/aYCPQwLVci0rzMMHitYakkzd44fh2D2v/C0M28uGeFVRe U4K61w14dc7O61vy6HLw69YomgTeCel1FL5Rf4yZNv5UiWV4ThhsBdNLnKNhWLtoSC nlvgGsH0jCF2odg8LfW0IDkyQRZCu6sCO/SsJHDwy29ARSzBJ/Nmt9K/izXA0Lf278 jQx0yR1DpkEvEW/QHtg8wflDM3ox4Hid1RJHJpThFAY+S6JdVxeXRQXFqCVx4U1dV6 yrZaDShVrDS8w== Date: Thu, 20 Mar 2025 14:40:52 -0700 From: Luis Chamberlain To: Christoph Hellwig Cc: 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, kbusch@kernel.org, sagi@grimberg.me, axboe@kernel.dk, joro@8bytes.org, brauner@kernel.org, hare@suse.de, willy@infradead.org, 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: <20250320141846.GA11512@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250320141846.GA11512@lst.de> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 02FAA160008 X-Stat-Signature: ho5w4et81qbs6b5uj3caunb9aq7hexaq X-Rspam-User: X-HE-Tag: 1742506854-521059 X-HE-Meta: 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 H4Y7at7b /macDnRIaHdEeCA9LtNKkufkGyHWj0D9UjqHjU+Xy0B+lmn9bd/svX8wKtCx4mhMwTYp2dgP3TJOId1I7zkeud3XqDXvxPdf2VJ/fne7s6eLrmaLB6ACc4pEb/g3tk6lWlRtaGgjdeF+OQzoPPk0UE3aUFBrWT9geeK6nFOL7AKbpmTUpFdBZJbJ65sYqcQe5gbzC7D8mH2FYIwJ6ZnY4XB3SkkpdpIwzOfPqwZWTcQBEdKaupE69DdsfBYLT76LfdoY+8XoGeOWes8Hltic+TNu5yqMgeZxR3IbCBFAQ+vNSjqMc04IeF7+lzFgnU94YEK5gPlA7qfoZ7kM= 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 03:18:46PM +0100, Christoph Hellwig 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. > > No, we absolutely haven't. I'm regularly seeing multi-MB I/O on both > SCSI and NVMe setup. Sorry you're right, I should have been clearer. This is only an issue without large folios for buffered IO, or without scatter list chaining support. Or put another way, block driver which don't support scatter list chaining will end up with a different max IO possible for direct IO and io-uring cmd. > > This is due to the number of DMA segments and the segment size. > > In nvme the max_segment_size is UINT_MAX, and for most SCSI HBAs it is > fairly large as well. For Direct IO or io-uring cmd when large folios may not be used the segments will be constrained to the page size. Luis