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bh=5HhwnTeHEt+NjdQZ0IEPNu7Xi23jc3U/hYhWJffOVLY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=gbHDg+F7o02qr1+zS/Ce/1wGsbRYhWnb9S5/cNXzn6LUnGYfnuDTth5KZAYMF/ONO /6yxAPiuddWLk5FN7T5fQ+Xh9NKmAXDohX/0mdnjjhOF5uzETeXg1dH0MjBJNpsQ7N R1s2H+Uv0se7TarcsK+bV0ylmU54WH/OfiSZt3voHpMXzSkfs3hDJRXiaoMvTF2I20 BstKpmA9bcchQ7JWreVjAd2MO7F8jZPaB6zeBd75Y/iWJ48w6rRepNd3ErNiDmkn+Y WuMn39iuoHUKlE3ExBcS68b416nm8s7bRMOcqDTrIImqBimpvzrpqLEIhqcWOXeKVJ lt1JsJdC7NwoQ== From: SJ Park To: SJ Park Cc: Andrew Morton , Liew Rui Yan , stable@vger.kernel.org, damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v3] mm/damon/core: fix unconditionally skip last region Date: Tue, 8 Sep 2026 07:51:32 -0700 Message-ID: <20260908145133.105111-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260908134739.96919-1-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: CCF63A000D X-Stat-Signature: x41xq3iiaoa9f6nd67qdfatxka3dba63 X-Rspam-User: X-HE-Tag: 1788879100-259677 X-HE-Meta: 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 bQ2uJ7CL YwyuGz3QOTzzoZjG35WwxyxtUdj87L0aQAFt2WmqEIJc0mVyh0wT4GYyqOCg3rY4pv4/vnqTFt6TPymXxuRy9GTujPCNqRF44OOrr6EbCkVON0g9lBB99T4EeamRdqnP3k/VhAtQGBXsDyclYBytR6V3GrNVn+P1wzmewZajPFet3DbGFuKJF/0OJoYDPP2n+PMg6/NDZWo+k5M5LOHVqrEX9Euss1Ti3ZrnDROcGRY532Bp3Rk2NXAqUvO5+o2K2LB6g Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 8 Sep 2026 06:47:38 -0700 SJ Park wrote: > From: Liew Rui Yan > > 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. Sashiko found a pre-existing issue that I'm separately working on. It is no blocker for this patch. Thanks, SJ [...]