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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1rGi2K-008Qjo-Oi; Fri, 22 Dec 2023 16:06:08 +0000 Date: Fri, 22 Dec 2023 16:06:08 +0000 From: Matthew Wilcox To: Keith Busch Cc: Viacheslav Dubeyko , Bart Van Assche , Hannes Reinecke , lsf-pc@lists.linuxfoundation.org, linux-mm@kvack.org, linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, "linux-nvme@lists.infradead.org" Subject: Re: [LSF/MM/BPF TOPIC] Large block for I/O Message-ID: References: <7970ad75-ca6a-34b9-43ea-c6f67fe6eae6@iogearbox.net> <4343d07b-b1b2-d43b-c201-a48e89145e5c@iogearbox.net> <03ebbc5f-2ff5-4f3c-8c5b-544413c55257@suse.de> <5c356222-fe9e-41b0-b7fe-218fbcde4573@acm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 759041A001C X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: a85zd71pfebyghkdh8w7tum4poj11o7r X-HE-Tag: 1703261179-33603 X-HE-Meta: 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 xAlj+zY+ GFer/SmCUCdBsNL1looKuQnl/hf7zIOJUeego/QlJuWS1/dyfhH4LOj0mc6oAGKsVEC/hRTYpOUQ6PzxlaDFXwLOewKZfCpVeWMZw3vucNc/M4GapsW1iJ+mQnzWWHD6zYP5uEyxVpSfx2jWmSUIgqqxuxY7xHXM66EcjwBscO7MuGZl7SBmLIA2cLA== 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, Dec 22, 2023 at 08:10:54AM -0700, Keith Busch wrote: > If the host really wants to write in small granularities, then larger > block sizes just shifts the write amplification from the device to the > host, which seems worse than letting the device deal with it. Maybe? I'm never sure about that. See, if the drive is actually managing the flash in 16kB chunks internally, then the drive has to do a RMW which is increased latency over the host just doing a 16kB write, which can go straight to flash. Assuming the host has the whole 16kB in memory (likely?) Of course, if you're PCIe bandwidth limited, then a 4kB write looks more attractive, but generally I think drives tend to be IOPS limited not bandwidth limited today?