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[209.85.208.41]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b55d9525bdesm958179666b.78.2025.10.13.09.07.11 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Oct 2025 09:07:11 -0700 (PDT) Received: by mail-ed1-f41.google.com with SMTP id 4fb4d7f45d1cf-631df7b2dffso1397884a12.1 for ; Mon, 13 Oct 2025 09:07:11 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCWFCxXEXXtR0DYMNCXr/Eq0oDd0qoCZNXO4toQcnFP9IwYVgOb7Z4aq02TPmtEH6ZrCD4FR236jdg==@kvack.org X-Received: by 2002:aa7:d45a:0:b0:62f:8bad:76e5 with SMTP id 4fb4d7f45d1cf-639baf07534mr17910768a12.5.1760371631299; Mon, 13 Oct 2025 09:07:11 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Linus Torvalds Date: Mon, 13 Oct 2025 09:06:54 -0700 X-Gmail-Original-Message-ID: X-Gm-Features: AS18NWBfLjf3F5D1SH907b2VJtHoEseavJA7J2wgEzyIuzyFb1rK7aIuY2U6g6g Message-ID: Subject: Re: Optimizing small reads To: Kiryl Shutsemau Cc: Matthew Wilcox , Luis Chamberlain , Linux-MM , linux-fsdevel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Queue-Id: 4D6BB180012 X-Rspamd-Server: rspam02 X-Stat-Signature: 5xn34dortk94zwajgu1zk3ekgap7cbw6 X-HE-Tag: 1760371634-190651 X-HE-Meta: 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 4eVg+wl4 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 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 Mon, 13 Oct 2025 at 08:35, Kiryl Shutsemau wrote: > > The patch is below. Can I use your Signed-off-by for it? Sure. But you can also just take ownership. > Here's some numbers. I cannot explain some of this. Like, there should > be zero changes for block size above 256, but... I'd assume it's the usual "random cache/code placement" thing. The numbers seem reasonably consistent, and guessing from your table you did basically a "random file / random offset" thing. And even if you go "but with random files and random offsets, cache placement should be random too", that's not true for the I$ side. So you could have some unlucky placement of the helper routines (like the iov stuff) that hits one case but not the other. > 16 threads, reads from 4k file(s), MiB/s > > --------------------------------------------------------- > | Block | Baseline | Baseline | Patched | Patched | > | size | same file | diff files | same file | diff files | > --------------------------------------------------------- > | 1 | 11.6 | 27.6 | 33.5 | 33.4 | > | 32 | 375 | 880 | 1027 | 1028 | > | 256 | 2940 | 6932 | 7872 | 7884 | > | 1024 | 11500 | 26900 | 11400 | 28300 | > | 4096 | 46500 | 103000 | 45700 | 108000 | The high-level pattern is fairly clear, with the big improvement being in the "small reads hitting same file", so at least the numbers don't look crazy. Linus