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Mon, 25 Dec 2023 00:55:27 -0800 (PST) Received: from smtpclient.apple ([2a00:1370:81a4:169c:d097:b658:f57b:dbcf]) by smtp.gmail.com with ESMTPSA id v17-20020ac25611000000b0050e75afd92csm628185lfd.212.2023.12.25.00.55.26 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Dec 2023 00:55:26 -0800 (PST) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3696.120.41.1.4\)) Subject: Re: [LSF/MM/BPF TOPIC] Large block for I/O From: Viacheslav Dubeyko In-Reply-To: Date: Mon, 25 Dec 2023 11:55:23 +0300 Cc: Keith Busch , 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" Content-Transfer-Encoding: quoted-printable 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> To: Matthew Wilcox X-Mailer: Apple Mail (2.3696.120.41.1.4) X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 747B31C001B X-Stat-Signature: hzam48zmkdbgqbnt36yfboe16zy9j47z X-HE-Tag: 1703494529-218015 X-HE-Meta: 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 Bh1hIbGs 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.002028, 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 Dec 22, 2023, at 7:06 PM, Matthew Wilcox = wrote: >=20 > 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. >=20 > 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? >=20 Fundamentally, if storage device supports 16K physical sector size, then I am not sure that we can write by 4K I/O requests. It means that we = should read 16K LBA into page cache or application=E2=80=99s buffer before any = write operation. So, I see potential RMW inside of storage device only if = device is capable to manage 4K I/O requests even if physical sector is 16K. But is it real life use-case? I am not sure about attractiveness of 4K write operations. Usually, file = system provides the way to configure an internal logical block size and = metadata granularities. Finally, it is possible to align the internal metadata = and user data granularities on 16K size, for example. An if we are talking about = metadata structures (for example, inodes table, block mapping, etc), then it=E2=80=99= s frequently updated data. So, 16K will most probably contains several updated 4K = pieces. And, as a result, we have to flush all these updated metadata, anyway, = despite PCIe bandwidth limitation (even if we have some). Also, I assume that to = send 16K I/O request could be more beneficial that several 4K I/O requests. = Of course, real life is more complicated.=20 Thanks, Slava.