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bh=R/ExsJARLlh4YfLuTV4QZWOBWCnroOAl4CtLg4Wbva8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=e7iC1y6H0Esa9kFZr5h4N5HEyHSq1fV4D0C028OIM5GxG2NOGDRD5QZBrxWRal5oj Q7u6kSz3IwmZRAabxKbdKnu81tpCG8WlZM8WDOVgCi1mIJg/Tg06EiVHEQqBAFag/g 9nIjgX5mLSFs61vNnv2D7sxDHWqRUlbp15YQPaGen+y8vIvJdBfpblsNI8TVp1CUxd nEsxCkSR1jq5gYYSjs+DQhUg2O0IJ5fXdzKN4BznUimxYPwPaAC+PPsC8EK5L7NS55 M5r50z6y1x/hh+sY7KiflyTCxFZyjmotgs6cnzax6Sd+J/IOYgPtm+amyOgyhyoRw2 w0aDJDpvsKDxg== From: SJ Park To: Liew Rui Yan Cc: SJ Park , Andrew Morton , damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] mm/damon/core: fix unconditionally skip last region Date: Sun, 30 Aug 2026 11:14:44 -0700 Message-ID: <20260830181445.104859-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260830063159.6347-1-aethernet65535@gmail.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 64C6FA0008 X-Stat-Signature: rwzap9ktkety75m19noyd874ujdpfret X-HE-Tag: 1788113693-191510 X-HE-Meta: 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 XqYluqqk VqE7B3tCFeuNrEhmr3bviBzB1V4yGOvC7PRdNF1TILD3ohjZJpDqGQXCxmT3ok20ITSWCO5+ZjDW49nv49s3IatEWl1KCI3VadaOrjlrl+n84UBuQbCs3e1ZgOeyGHPdLd7OmQZDYxRDReDrxP7kuxdC6ZD75PdNh+1gKmX59TMtggfasfTrTOJ7UYZw2WeWkSYSSmpOw4Fc9PLwhrVlCQQi9xkYRQpATd13voiH5tT9cwbkOcqxJbkap/imlZIzVRiwf Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, 30 Aug 2026 14:31:50 +0800 Liew Rui Yan wrote: > Once quota set, the charge_{target,addr}_from unconditionally skips and > resets at the last region of the tracked target, so the last region can > be skipped even when it has not been processed. > > Example: > > 1. Target has 2 regions: R1 (0-100 bytes) and R2 (100-200 bytes). > 2. Quota is configured to process only 100 bytes per window. > 3. Window 1: Processes R1 (0-100). Quota is full. charge_{target, > addr}_from is saved at (Target, 100). > 4. Window 2: The loop reaches R2. Because R2 is > damon_last_region(t), the old code unconditionally returns true, > skipping R2 entirely and resetting the charge_{target,addr}_from. > > Result: R2 is permanently skipped even though it has never been > processed. > > However, it is important to note that this is a very minor issue. This > is because it is triggered only when the previous window saved/kept > charge_{target,addr}_from, and in the next window, all regions except > the last region were skipped by damos_skip_charged_region(). > > Fix this by only resets the charge_{target,addr}_from when last region > is reached, only skips when it applied or cannot split. Looks good to me! > > Fixes: 50585192bc2e ("mm/damon/schemes: skip already charged targets and regions") > Cc: # v5.16.x > Signed-off-by: Liew Rui Yan Reviewed-by: SJ Park Thanks, SJ [...]