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Sat, 19 Sep 2026 12:09:39 -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: [RESEND PATCH] mm/damon/tests/core-kunit: add test for unconditionally skipping the last region Date: Sun, 20 Sep 2026 03:09:10 +0800 Message-ID: <20260919190953.86705-1-aethernet65535@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260919160725.86256-1-sj@kernel.org> References: <20260919160725.86256-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 598381C0005 X-Stat-Signature: wmgryah6kzok7yp54m13iwxtnui9w5yq X-Rspam-User: X-HE-Tag: 1789844981-874811 X-HE-Meta: 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 LYie0rc3 W+o3WQLoZqtNMkYPNlHLEWXu4pP3Eyl60HE8DC5xpjIvThD7U2VfNyYy4sCGwdvSOpiKGo0N6oeD8blppzWdZLKsZgYmALQG1cbcuyXQQTt2CQqBUs6SU7L1QoOaOaIIwYkgBpZgSr3Le7kY/mm4L8aHsYhYBeWT3HWNFGNHecfW8nnsFrqHT1LFagSm4kf0pMoJVXnMeVkB066mRM+RpwCNXbLW1c9OVwbXNxdZpMmb4gw6qFc0OJvBlkt+fzxahA0UBHXGKe7TCMmHdY3u8IhgWlhQ/CkRUhs6j/hkAe3a+r5+QLwY5rSu5puukLLFQUzggIdS8rBnNGkTVvGJyzjp8S03MtCbdbUEbzk3NHwniRRqJVWOx9Lgr4iOnd3LXmqWBqHv0YZEi6yi11gH7sR+XCJ9z+Aqy0n9+e0TBGli7CqgVJaZxthaFwnnwOuokWRTpD/MjFhru/e21JJKYTFNGGA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, 19 Sep 2026 09:07:25 -0700 SJ Park wrote: > On Sat, 19 Sep 2026 16:01:58 +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. > > > > Signed-off-by: Liew Rui Yan > > Other than a trivial style that I commented below, > > Reviewed-by: SJ Park > > [...] > > +static void damon_test_last_region_quota_reset(struct kunit *test) > > +{ > [...] > > + t = damon_new_target(); > > + if (!t) { > > + kunit_skip(test, "target alloc fail"); > > + } > > Let's drop braces for single line, as suggested [1] in coding-style. I will change this in next revision. By the way, Sashiko reported an issue [1]: min_region_sz is not power-of-2. While this do not cause any real issue in this test, non-power-of-2's min_region_sz is not legal. Should min_region_sz initial value set to power-of-2 value (e.g., PAGE_SIZE) in the next revision? > > [1] https://docs.kernel.org/process/coding-style.html#placing-braces-and-spaces > [1] https://lore.kernel.org/damon/20260919081239.8A3D91F000FF@smtp.kernel.org Best regards, Rui Yan