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Wed, 02 Sep 2026 08:33:41 -0700 (PDT) From: Kunwu Chan X-Google-Original-From: Kunwu Chan To: SJ Park Cc: Kunwu Chan , Kunwu Chan , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 05/12] mm/damon/sysfs: remove probes number validation Date: Wed, 2 Sep 2026 23:33:33 +0800 Message-ID: <20260902153334.4034394-1-kunwu.chan@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260902143706.88115-1-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 6608A1C0002 X-Stat-Signature: pytytekrdwnufkptfnecxxtt7fffn9q8 X-HE-Tag: 1788363223-440322 X-HE-Meta: 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 ls0E9R7G aNmFADkAqKlR++q1Gj5wO4OnHdYwuksP5cMg9yidNybSvOnDiZTAiVBYDEKFSCN2b9eSSs9d0HRCFD4XVRQH29uaNgZw5XF1Z0m1VI9uHd4yOw3Dzm3rZ+vSnE1bq84PMnaaBrm4pLQmOR2o6R77xGfgZCe8HavjIec8jpStXk9n4TWyJktrNrUH2XqDBIH6mGs6XlQckTlDnyOkH8ozqTdtbciCX/Ah3C82emgvgQ+RgN5dE9tibvXtHDNETt6b2ndI0xjyCTRmLNHwNu4Dw8BWYLnj5GxBIsG64UI84jjc8oohJYk3lzP17cYC2bQ7ypPyfYcq4bit1VL5gf+nyPpEXx+/SQf8Phmx1RowrygDfhoHQEg5UW6bliczczYN/g3Ok5wirtyhREoMkO5rQdOe5ArLeYxZlxOnVLeEDfTzNyXfO8P684SKSEPwlveEpxBOV Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 2 Sep 2026 07:37:06 -0700 SJ Park wrote: > On Wed, 2 Sep 2026 22:07:13 +0800 Kunwu Chan wrote: > > > On Tue, 1 Sep 2026 22:47:38 -0700 SJ Park wrote: > [...] > > I was wondering whether DAMON_MAX_PROBES is purely a core invariant > > or also an interface constraint. > > Thank you for reviewing my patch and raising this question! > > > > > With this change, sysfs allows nr_probes larger than > > DAMON_MAX_PROBES and damon_sysfs_probes_add_dirs() will start creating > > probe objects before the configuration is later rejected by > > damon_valid_probe_params(). > > > > Since nr_probes directly controls the number of sysfs objects created, > > do we still want to keep an early check here? > > > > I agree that the core validation is required for non-sysfs callers, > > but I am not sure whether this particular limit should be duplicated > > at the sysfs layer. > > I agree the user experience may be not that good. > > In my humble opinion, however, keeping code simplicity is more important than > the user experience here. After all, DAMON_SYSFS is recommended to be used by > another high level tools like DAMON user-space tool (damo) rather than human > fingers. The user-space tools like damo can do the early check. > > Please feel free to let me know if you have any other opinions or questions. Hi SJ, Thanks for the explanation. I agree that keeping the invariant validation in the core layer avoids duplicating the limit in multiple places. Your point about DAMON_SYSFS being mainly consumed by higher-level tools like damo also makes sense. My concern was mainly about the temporary creation of sysfs probe objects before the configuration is rejected, rather than the user-facing error message. Given that the number of probes is bounded by the core invariant anyway, I agree that keeping the validation centralized is a reasonable trade-off. Thanks for clarifying. Reviewed-by: Kunwu Chan Thanks, Kunwu > > > Thanks, > SJ > > [...] > Sent using hkml (https://github.com/sjp38/hackermail)