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Tue, 10 Nov 2026 20:23:28 -0800 (PST) Received: from LAPTOP-KD1TH5BD.tail375eb4.ts.net ([47.11.96.168]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1b3b5b11150sm15985536c88.5.2026.11.10.20.23.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Nov 2026 20:23:27 -0800 (PST) From: Gopal Malaviya To: alireza.haddadi@it.uu.se Cc: jack@suse.cz, willy@infradead.org, akpm@linux-foundation.org, vishal.moola@gmail.com, fujunjie1@qq.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, regressions@lists.linux.dev, tracekotae@gmail.com Subject: Re: [PATCH] mm/filemap: let sequential faults restart mmap readahead Date: Wed, 11 Nov 2026 04:23:10 +0000 Message-ID: <20261111042310.191979-1-gopalmalaviya53@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261109-mmap-miss-v1-1-8b44b33f3358@it.uu.se> References: <20261109-mmap-miss-v1-1-8b44b33f3358@it.uu.se> X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 2497E20005 X-Stat-Signature: 4zo8s7iut93y5xtm438dksn1ra4zojkb X-Rspam-User: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1794371010-237346 X-HE-Meta: U2FsdGVkX19I0OmDeyfeaj7o8gtoOiVWIpH+iNwRfC9n2W272wjrJI3pG0TMk1QIeRA5IK8bYDPYZ0mOuD4KWE25Xkn/06mB3qSfDft95iXU56xOx1FpOl8vaoifjh+K9V6JYgSFt1u/Mydiw1LtaUQSUY+CfhrxYN4/jRE2hHyJHlmPwW1NxusvObCmLUiSTVa8PkktB+NuEzIcgX3NlCdGkqa5XrQM/6hUM967AFs+FieuhPQoumq4ddaPR0yQh9EsejRokwc4t+gLdUQfy1bRTqGuY4jIU5WssSDV2vc8kqJKUfoYx5GnOQrAPsnCVBCV6xYJXKk9/3HMVEFn6GdTVDr2ykfTZCXVgIjm1ff7rpFN2EkmstsibjR88JUxHYLQJWdUnijWtF9EqIy6goTJy2HqAW/3QXtPd8AbY71flNCiVU56vvURnumoeQlxJrzPY2ZxMWmDUCjmTBAJMKjpfFP8aDAsMVz9w6MvRRXa7q0KHDXTH1Ia1znpYzsJm9Q4VxhVceYqtI7sgwXoQHRj8nCamEbx5LsFCLROisFHU2PRj4DkLntGAHxy4XYJH/RmiiLeERkQuzx6zARI3RNwVHoJFkdo5Q/k2bmCoKXtlG3dJyhKvJw8+zXFgmv4dXaWfX9Ddf2neBJTwdlRAGL/BQbyNCd5/ir6cvAphxSXMC6Am8beICA8cjprasJi0CX8Unw1veXyrY+16/DWSqDifpBwoXFyd5lJg3VzprwfzVuFH9vPew6cIcdNcb7+rADtPICagwx1m1fCot/rpdTJo79SNFMkqmD1crH8hJFLdVDRHr0LU9TqcoJ6ZTcJRieAl/YiCi3CzY5bmZjCcceYl+0OxgTrIrfnGUz8l3jKHhzmk4IQCS9wWVS2efL5wur+HJoXoAWzDyMZgXYWls9jgWs1fkyOPMMpRpqAoLvOzNyFRBLHK3oPYXSuMb+gAxRrA+gwTR8kc2CLUOv mSKRvAp9 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Hi Alireza, I had sent a different fix for the same regression [1], reported by Trace in [2]. Jan prefers yours, so I have dropped mine. I ran your patch, also with the v2 change you describe to Jan, through the tests I had: a KVM guest (x86_64, 2 vCPUs, 3 GiB), mm-hotfixes-unstable as of 2026-11-08, ext4 and XFS with 16 KiB blocks on virtio-blk, read_ahead_kb 128 unless noted. The reproducer from [2] (2000 single-page faults 1 MiB apart, then a 64 MiB sequential read), major faults in the sequential part: base as posted with v2 change ext4 16384 2 2 XFS, 16 KiB blocks 4096 4096 2 Touching 1% of the pages of a cold 20 GiB file, larger than memory, in random runs of 1, 2 or 4 adjacent pages, MiB read from disk with the v2 change (first of two runs; the second was within 10%): read_ahead_kb 128 read_ahead_kb 8192 base with v2 base with v2 random 259 234 1057 1070 stride 2053 pages 271 236 992 992 random 2-page runs 257 373 1135 2538 random 4-page runs 240 1146 1200 57748 The 4-page runs at read_ahead_kb 8192, which is what this guest's virtio-blk disk gets by default, read about 48 times more. As far as I can tell, each run now has two misses and up to two hits on the new window, so mmap_miss stays around MMAP_LOTSAMISS, and each time it is back at the limit the next random miss gets the full 8 MiB read-around. My patch ran into the same and kept mmap_miss at its cap on that path; something like that may help here, but you and Jan know this better. On the Fixes tag: with the commits of the series built one by one, commit 0b9c0aeba938 ("mm/filemap: count only the faulting address as a mmap hit") alone does not show the problem (1 major fault with the reproducer), and commit 9b0fcac3cfe7 ("mm/filemap: do not count FAULT_FLAG_TRIED retries as mmap hits") does (16384). [2] is the same regression, in case you want to add Reported-by and Closes tags for regzbot. I am happy to run these again on your v2. The tests were set up with the help of an AI assistant. [1] https://lore.kernel.org/all/20261109091444.128521-1-gopalmalaviya53@gmail.com/ [2] https://lore.kernel.org/all/20261105192517.228523-1-tracekotae@gmail.com/ Thanks, Gopal