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Mon, 25 Dec 2023 00:12:16 -0800 (PST) Received: from smtpclient.apple ([2a00:1370:81a4:169c:d097:b658:f57b:dbcf]) by smtp.gmail.com with ESMTPSA id k10-20020a2e920a000000b002ccad70dacfsm1147930ljg.26.2023.12.25.00.12.15 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Dec 2023 00:12:16 -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 11:12:12 +0300 Cc: 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: <0C457D1B-4923-45E6-A481-28C92B66243E@dubeyko.com> 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: Keith Busch X-Mailer: Apple Mail (2.3696.120.41.1.4) X-Rspam-User: X-Stat-Signature: iqk64apori8oye479qhnnuhqu3r1qqhy X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: BDCC940005 X-HE-Tag: 1703491938-615699 X-HE-Meta: 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 gHZrqKug 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.003172, 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 6:10 PM, Keith Busch wrote: >=20 >=20 >=20 > Other applications, though, still need 4k writes. Turning those to RMW > on the host to modify 4k in the middle of a 16k block is obviously a = bad > fit. So, if application doesn=E2=80=99t work with raw device directly or not = use O_DIRECT, then we always have file system=E2=80=99s page cache in the middle. It = sounds like 4K write operation makes dirty the whole 16K logical block, from file = system point of view. Finally, file system will need to flush the whole 16K logical = block, even if 4k modification was only in the middle of 16K. Potentially, it could = sound like increasing write amplification. However, usually, metadata could require = smaller granularity (like 4K). But metadata is frequently updated type of data. = So, there is significant probability that, at average, 16K logical block with = metadata can be evenly updated by 4K write operations before flush operation. If we have = cold user data, then logical block size doesn=E2=80=99t matter because write = operation can be aligned. I assume that frequently updated user data could be localized at some = file=E2=80=99s area(s). It means that 16K logical block size could gather several 4K frequently = updated areas Theoretically, it is possible to imagine really nasty even distribution = of 4K updates through the whole file with holes in between, but it looks like some = stress testing or benchmarking, but not real-life use-case or workload. Let=E2=80=99s imagine that application writes directly to raw device by = 4K I/O operations. If block device supports 16K physical sector size, then can we write by = 4K I/O operations? =46rom another point of view, if I know that my application = updates by 4K I/O, then what=E2=80=99s the point to use device with 16K physical = sector size, for example. I hope we will have opportunity to make a choice between devices that = supports 4K and 16K physical sector sizes. But, technically speaking, storage device = usually receives multiple I/O requests at the same time. Even if it receives 4K updates = for different LBAs, then it is possible to combine several 4K updates into 16K NAND = flash page. The question here is how to map the updates into LBAs efficiently. = Because, the main FTL=E2=80=99s responsibility is mapping (LBA into erase blocks, for = example). Thanks, Slava.