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Sat, 26 Sep 2026 14:07:21 -0700 (PDT) From: Liew Rui Yan To: sj@kernel.org Cc: aethernet65535@gmail.com, akpm@linux-foundation.org, damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2] mm/damon/tests/core-kunit: add test for unconditionally skipping the last region Date: Sun, 27 Sep 2026 05:07:09 +0800 Message-ID: <20260926210737.8837-1-aethernet65535@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260925090239.47821-1-sj@kernel.org> References: <20260925090239.47821-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: ge6sftyp1twsfc7as13pjmh88rmwuxfp X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 451A240009 X-HE-Tag: 1790456843-784232 X-HE-Meta: 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 U3CIOpbq gG0HuRNu0JLsLl9JnzmkLzid6G3FWl0BKB6d3ZyZEnrrzKiWlwSp62bsMbjIVNnc1QyCe9F8KjDClH9XDfnJgKXCixdDdzPNSHl/gZvyuVZ5IOcp5D/RbY3/daMkqAoYZllAmS3Qfr7tdBbUWB9MmHV1DH0yCa9d0eOcozJWjqgXnOB6VKu819NeZHRtr60VJFch02o0vL/ws6xvDRjbFcAuWNyBMq1XS2E8ulBo3xw28QAMdAGrASiy8aR83eWnniMGQIl84Re+LPaLr3MM2/YTKQP1ho2NNQA+IYExezLgc6MIn46faeulsZWhSnoHrXh4FrEhG+fTxImUog+duyIsTP0cL4Squ/+Nduc/j4yIo/OZDJnfiGlG1FnaFwJTA3otzdNgJK6qhU9rfbW3fWBg1eznht6RhcFa9aqhs252GuIyXfzJpgue8lg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 25 Sep 2026 02:02:38 -0700 SJ Park wrote: > On Fri, 25 Sep 2026 12:53:35 +0800 Liew Rui Yan wrote: > > > Commit 50585192bc2e ("mm/damon/schemes: skip already charged targets and > > regions") introduced a minor issue that causes the last region to be > > skipped before it is 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. > > > > Add a test to prevent this regression in the future. > > The bug is fixed by commit b3723b596b54 ("mm/damon/core: fix unconditionally > skip last region"), which is merged into the mainline for 7.3-rc5. Could you > update the commit message to mention the fix, rather than the original bug? > The fix commit already has a quite good description of the bug, so I don't > think we need to duplicate it here. > > Other than that, looks good to me. Okay, I will change the commit message in the next revision. Commit b3723b596b54 ("mm/damon/core: fix unconditionally skip last region") fixed a minor bug. Add a KUnit test case to cover this behavior and prevent regressions in the future. [...] Best regards, Rui Yan