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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-49c605e5b2fsm12637227f8f.40.2026.11.14.10.10.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 14 Nov 2026 10:10:35 -0800 (PST) From: David Carlier To: SJ Park Cc: Aveline Noir , Andrew Morton , damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/9] mm/damon/stat: avoid 32-bit overflow in idle percentiles Date: Sat, 14 Nov 2026 18:10:34 +0000 Message-ID: <20261114181034.2665113-1-devnexen@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20261102150757.93058-5-sj@kernel.org> References: <20261102150757.93058-5-sj@kernel.org> X-Mailing-List: linux-kernel@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 Hi SJ, Aveline, The value stored a few lines below has the same problem on 32-bit: damon_stat_idletime(region) * (long)c->attrs.aggr_interval / USEC_PER_MSEC; The product is the region's idle time in microseconds, held in a 32-bit long, so it wraps once a region has been idle for more than about 36 minutes, whatever the intervals are. The cold-end percentiles then come out negative or wrong. Doing the multiply in s64 with div_s64() would keep the sign and avoid it. Hope it helps !