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Wed, 02 Sep 2026 01:44:46 -0700 (PDT) From: Liew Rui Yan To: SJ Park Cc: Andrew Morton , damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Liew Rui Yan , stable@vger.kernel.org Subject: [PATCH v2.1] mm/damon/core: fix false positive in damos_quota_is_full() when esz is zero Date: Wed, 2 Sep 2026 16:44:45 +0800 Message-ID: <20260902084445.27170-1-aethernet65535@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When setting goal_tuner to 'temporal', if the goal is achieved, quota->esz_bp will be set to zero. In this case, damos_quota_is_full() will always return true, even if no regions have been tried to apply at all. This causes qt_exceeds to increase unexpectedly. Fix it by: - Returning false in damos_quota_is_full() when quota->charged_sz is zero. - Adding an early exit in damon_do_apply_schemes() for schemes with zero esz. Fixes: c7ec7d5f6b3d ("mm/damon/core: handle # v7.2.x Signed-off-by: Liew Rui Yan --- Changes from v2: - v2: https://lore.kernel.org/damon/20260902081825.18931-1-aethernet65535@gmail.com - Changed patch title, v2 title is truncated. Changes from v1: - v1: https://lore.kernel.org/damon/20260901105925.106186-1-aethernet65535@gmail.com - Changed the check in damos_quota_is_full() from '!quota->esz' to '!quota->charged_sz', because the former is an upper bound, while the latter represents the actual quota usage. - Added an early exit in damon_do_apply_schemes() to prevent a scheme with zero esz from being evaluated by damos_quota_is_full(). - Changed patch title, original title: always return false when esz is zero --- mm/damon/core.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index 8e3ded1a2cf6..de78ad56c8b3 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2560,6 +2560,8 @@ static bool damos_quota_is_full(struct damos_quota *quota, { if (!damos_quota_is_set(quota)) return false; + if (!quota->charged_sz) + return false; if (quota->charged_sz >= quota->esz) return true; /* @@ -2666,6 +2668,9 @@ static void damon_do_apply_schemes(struct damon_ctx *c, if (!s->wmarks.activated) continue; + if (!quota->esz) + continue; + /* Check the quota */ if (damos_quota_is_full(quota, c->min_region_sz)) continue; -- 2.55.0