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Wed, 02 Sep 2026 07:07:22 -0700 (PDT) From: Kunwu Chan X-Google-Original-From: Kunwu Chan To: SJ Park Cc: 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 22:07:13 +0800 Message-ID: <20260902140714.4023700-1-kunwu.chan@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260902054747.99370-6-sj@kernel.org> References: Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Tue, 1 Sep 2026 22:47:38 -0700 SJ Park wrote: > DAMON sysfs interface is disallowing >DAMON_MAX_PROBES nr_probes input, > since DAMON_MAX_PROBES is the upper limit of probes per DAMON context. > The core layer is validating the upper limit again, though. It is > preferred to let DAMON API callers such as sysfs interface to set > parameters in flexible ways, and do parameters validation in the core > layer. Drop the duplicated validation in the sysfs interface. > > Signed-off-by: SJ Park > --- > mm/damon/sysfs.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c > index 7ec14f48d157a..b576e97cbfdb8 100644 > --- a/mm/damon/sysfs.c > +++ b/mm/damon/sysfs.c > @@ -1479,7 +1479,7 @@ static ssize_t nr_probes_store(struct kobject *kobj, > > if (err) > return err; > - if (nr < 0 || nr > DAMON_MAX_PROBES) > + if (nr < 0) Hi SJ, Thanks for the cleanup. I was wondering whether DAMON_MAX_PROBES is purely a core invariant or also an interface constraint. 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. Thanks, Kunwu > return -EINVAL; > > probes = container_of(kobj, struct damon_sysfs_probes, kobj); > -- > 2.47.3 > Sent using hkml (https://github.com/sjp38/hackermail)