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Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kairui Song , Qi Zheng , Shakeel Butt , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , "Paul E . McKenney" , Pedro Falcato , Harry Yoo , Luis Chamberlain , Ilya Gladyshev , Jaegeuk Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, fuse-devel@lists.linux.dev, kernel-team@meta.com Subject: [RFC PATCH 13/18] mm/filemap: store the end of a read in f_ra only when it changes Date: Mon, 19 Oct 2026 16:49:06 +0100 Message-ID: <20261019154913.1765974-14-kas@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20261019154913.1765974-1-kas@kernel.org> References: <20261019154913.1765974-1-kas@kernel.org> X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit filemap_read() writes the end of every read to file->f_ra.prev_pos. Threads that read through one open file all write that cache line, on every read. The value often stays the same, as for reads that start at the same offset each time. Store it only when it changes. Assisted-by: LLM Signed-off-by: Kiryl Shutsemau (Meta) --- mm/filemap.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/filemap.c b/mm/filemap.c index 53ec92279977..960d53b61d4b 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2941,7 +2941,9 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter, } while (iov_iter_count(iter) && iocb->ki_pos < isize && !error); file_accessed(filp); - ra->prev_pos = last_pos; + /* Readers sharing the file would bounce the line for nothing */ + if (ra->prev_pos != last_pos) + ra->prev_pos = last_pos; return already_read ? already_read : error; } EXPORT_SYMBOL_GPL(filemap_read); -- 2.54.0