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Wed, 02 Sep 2026 07:22:47 -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, stable@vger.kernel.org Subject: Re: [PATCH v2.1] mm/damon/core: fix false positive in damos_quota_is_full() when esz is zero Date: Wed, 2 Sep 2026 22:22:31 +0800 Message-ID: <20260902142254.5328-1-aethernet65535@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260902141001.86733-1-sj@kernel.org> References: <20260902141001.86733-1-sj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: g6nrm6sjeioo7ygjrn1khbuyy756k7ya X-Rspamd-Queue-Id: A0330100010 X-HE-Tag: 1788358969-649723 X-HE-Meta: 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 EYNfKGUM 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 02 Sep 2026 07:10:00 -0700 SJ Park wrote: > On Wed, 2 Sep 2026 16:44:45 +0800 Liew Rui Yan wrote: > > > 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. > > To me, this looks logically correct. Could this cause any user issue? Yes, I think this might cause unnecessary confusion for users, at least it did for me. I set quota_ms to 0 and set the target_metric for the quota goal to user_input (i.e., MemAvailable). In my use case, this caused esz_bp to be 0 most of the time. Also, because the quota->ms clamp was missing, esz wasn’t set to min_region_sz, it was actually set to 0. As a result, nr_tried is 0 (because damos_quota_is_full() in damon_do_apply_scheme() always returns true), but qt_exceeds increments once per second (likely because reset_interval_ms defaults to 1000ms / 1s). Best regards, Rui Yan