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Tue, 09 Dec 2025 04:20:54 -0800 (PST) MIME-Version: 1.0 References: <20251206224724.13832-1-rgbi3307@gmail.com> <20251207023625.44177-1-sj@kernel.org> In-Reply-To: <20251207023625.44177-1-sj@kernel.org> From: JaeJoon Jung Date: Tue, 9 Dec 2025 21:20:42 +0900 X-Gm-Features: AQt7F2q9hsT8FOu7rr45aQ_Azbmj4EMMy0e-8Rt-6hhhTyywnYIFfVlP3APSEdA Message-ID: Subject: Re: [PATCH] mm/damon: modified damon_call_control from static to kmalloc To: SeongJae Park Cc: damon@lists.linux.dev, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: tu9g6yu1atzryp8q5zcso3ogmeff7jin X-Rspam-User: X-Rspamd-Queue-Id: 0DC6A1C0012 X-Rspamd-Server: rspam01 X-HE-Tag: 1765282854-278360 X-HE-Meta: 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 iJts9NPJ O84fiZGV34UOGH8lw20J7Cbs7p2rkjMlSZZKewe60KeSctSXAt7lS6c0vVESUf9obSIaKqZY12+NxFsNG+5rI2v2gSkcILov83X7um6OMlY1bzID3ZBxrNhQLYgAmu946f0UNkXnXPMHFYRGyHuZzUgMOYBntZUpZYvoX8zywXidh5bzjvvubolOTz6wA59c6MSuj5q1E1PCQ6IyyiB2aIoxJCjnDeSNOLAGgXiZkxK622SnxQBxZFh2Wn8PYwRA6TEcCrE5qx+aRTRIwOw14HGosdDxnQX9x3aAoeMHvrWQzEw/hFSM633mLdhFmrcvdRSl7K0kohNeKjQS5D8iZGiu9dCuO18SGnCrf2jLbMYSCD+eZKI/cyxx3D60UV9dmSc0KQj6Lv/Dc3AGLOb3FESZNJtLelvLI5D8BG8kJ3iQixDVC778dmHYmqcfbx3zN+BVb X-Bogosity: Ham, tests=bogofilter, spamicity=0.000127, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello, SeongJae, Thank you for your detailed feedback. My patch has the advantage of removing the use of the damon_call_control.dealloc_on_cancel variable. Other than that, I agree with you pointed out. It's not a patch that significantly improves functionality, so I'm fine with doing whatever you decide. Thanks, JaeJoon On Sun, 7 Dec 2025 at 11:36, SeongJae Park wrote: > > On Sun, 7 Dec 2025 07:47:23 +0900 JaeJoon Jung wrote: > > > The damon_call_control structure is used by all damon modules. > > In mm/damon/sysfs.c, it is dynamically allocated with kmalloc(), > > It is only for refresh_ms handling damon_call_control. > damon_sysfs_damon_call() doesn't use kmalloc(). > > > and in > > the remaining modules, it is statically coded. > > I try not to use dynamic allocation when possible and *reasonable*, since doing > so eliminates the chances of bugs from dynamic allocation handling mistakes. > > > There are many daemon > > modules and they are designed to be used only when needed. It is more > > efficient to use kmalloc dynamically whenever needed as in damon/sysfs.c. > > I agree that is more efficient in terms of kernel size. Nevertheless, I don't > think it is a significant improvement, since it is only single data structure > per the DAMON module. The total number of DAMON modules is only five. Two > among those are samples. > > > Using damon_call_control dynamically and consistently has the advantage of > > eliminating the dealloc_on_cancel member variable condition and reducing > > code size. > > Disadvantage of this change is that it is adding four more dynamic allocations > that we need to cautiously maintain. It is not significantly increasing the > maintenance overhead. But, the advantage (kernel size reduction) also seems > only modest, if I'm not wrong. > > So I'm sadly have to say I don't think this change is really needed. > > Please let me know if I'm missing something, though. > > > Thanks, > SJ > > [...]