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bh=0ajyy7n+0qSH1YTBPHJg2ZBD7XeUrxHy6Kcj1EJImYg=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=TPTCykYLb7YyiJfftqIjfbRil9UPgYWqaphUQv4SNzGMIybk7zut1L7O8CycL0PEv Smo0NgFZGhnE+mBm7d9Btecxf57Ahxs29iz8mkXeRHCPAETLHr85sZIyWoN6caU4eI Ol7GIqDjsQJNf1roys0/r/YwrfJP37d3aGtuBGDBHiKYgYoKHl7VVo5s8XPI5BOU3q Jlv+0oj6r42VtAZvavVTNp0T2saIeiOJ1iLja14RovmpDMdwqr8eAnzS0XW8QkM8Lw 887397wb8fvNkInSWSXM7qeWGxayhLmWhlLO+BDB2X2DhcHaVwnIi73BFArxarkNqm vJrNG4eH9MRIg== From: SJ Park To: Wang Guangke Cc: SJ Park , akpm@linux-foundation.org, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] mm/damon/stat: avoid overflow in estimated_memory_bandwidth calculation Date: Tue, 3 Nov 2026 06:34:09 -0800 Message-ID: <20261103143410.87235-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261103034034.7978-1-gkwang@linx-info.com> References: X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: 1hxg31zjaz6n6bq3ycjni9zn8rkatdxp X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: BFC184000C X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793716458-982811 X-HE-Meta: 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 ujdZH978 dtJG8ZihEG1YAa2fvLz6B4iPs8lEck3ozhkU4z2nC3D6QccKTYJtX0bqPwaY/84IXYkmh9adVWcf+eflKNOBjTLw3xdOaXagEsLR6IxaYKBQ/tk6TGzzHRiXQBW6ORMTd1neMzodGGF6tmj9QT+rjv4q6rwnXIVgXdNJl1eMEg5ZYieme1/YDU3I3OvoW0N3R8FZsaUCms4Vj0En7BUU4lCWsyFJyG6OYTVmn+pI1G3pnQkaCFbZkuxAzrrkOhSY8K1lOzCMXnx4QsuK9IYHLvtEt+hUzzSLXyd1atVf9FqbD0DDbzfqh+9p9SnCu0vk/bE8U/pxexv3CJEG0QNdIZ2CcpmrQ87YAcvqx9RgqS4+hEx0= 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 Wang, On Tue, 3 Nov 2026 11:40:34 +0800 Wang Guangke wrote: > estimated_memory_bandwidth is calculated by access_bytes * > USEC_PER_MSEC * MSEC_PER_SEC (= USEC_PER_SEC) / aggr_interval, > and users read it via > /sys/module/damon_stat/parameters/estimated_memory_bandwidth. > > On 32-bit systems, access_bytes * USEC_PER_SEC overflows unsigned > long once access_bytes exceeds about 4294 (U32_MAX / USEC_PER_SEC), > so users get a wrong value. > > Fix it by doing the calculation in 64-bit and splitting the division > into quotient and remainder. > > The issue was reproduced on a 32-bit system (qemu-system-i386): the > parameter estimated_memory_bandwidth reported 362 instead of the > expected 1926150; with the fix, the value matches the expectation. Looks good to me. > > Fixes: fabdd1e911da ("mm/damon/stat: calculate and expose estimated memory bandwidth") > Cc: > Signed-off-by: Wang Guangke Reviewed-by: SJ Park This patch is applied to damon/next [1] tree. I will repost it soon (~1 week) as an mm.git merge request. So, no action from your side is needed for now. [1] https://origin.kernel.org/doc/html/latest/mm/damon/maintainer-profile.html#scm-trees Thanks, SJ [...]