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Howlett" , Michal Hocko , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka Subject: Re: [PATCH] mm/damon/core: reject empty access pattern intervals on scheme commit Date: Tue, 3 Nov 2026 06:53:19 -0800 Message-ID: <20261103145319.88120-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261103105418.362459-1-xiaoleiwangxiaolei@gmail.com> References: X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-8.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam09 X-Stat-Signature: wnwq74z5w4dgedkczhznu6yp5gppko3t X-Rspamd-Queue-Id: ADE3E1C0005 X-Rspam-User: X-HE-Tag: 1793717607-547046 X-HE-Meta: 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 kBBPipXu yApJiVW+MU5/7AletD0RX95grq1WPlp1XyPdv+8cmb6ZRscE1IJoGpEfiYyeVoHMvqm0ZQ4ftZw7VdiVnE901Cm9RHdmgIYtVDQOyfOE/2KJZd5ewrkiGG0tW0nzFf8VyUJCHlXok1e1PdeX8nKYJ+3p1CgCwvTphnmAT7SYJMY0hDr6cMWWrptKRtwKvK1useDK9vBJpLsgD5UMDdxjs34crtoZe1vNcLvdaAH/AbBlDbWc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Tue, 3 Nov 2026 18:54:18 +0800 "Xiaolei Wang (Kaihong)" wrote: > DAMOS schemes accept access pattern bounds with min > max (e.g. > min_sz_region > max_sz_region). No input path validates the bounds: > damon_new_scheme() stores the pattern as is, and the sysfs ul_range > stores are plain kstrtoul(). > > At runtime __damos_valid_target() evaluates "min <= x <= max" for each > of the three pattern dimensions. A reversed interval is an empty set, > so every region fails the check and the scheme silently never matches > anything: nr_tried stays zero forever while the kdamond keeps running > normally. > > With such a reversed interval, damo starts normally (rc=0, kdamond > state=on), but nr_tried and nr_applied stay zero forever and the target > RSS does not drop. > > The same holds for the watermarks thresholds, which must be monotonic > (low <= mid <= high). > > Validate the access pattern and watermarks at the beginning of > damos_commit(), through which both new schemes (damo start) and online > updates (damo tune) pass. The documentation is not explicitly mentioning about the inputs (min > max and non-monotonic watermarks). But I was thinking it is not really difficult to infer this behavior based on the existing document. If my understanding of the documentation is not wrong, I find no problem at accepting the inputs and just behave as documented. It might look silly, but who knows the users have a creative reason to do that? As long as it is not causing a harm, just supporting it is better for both users and code maintainability, in my humble opinion. Pleae let me know if I am missing something. Thanks, SJ [...]