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charset=UTF-8 Date: Tue, 07 Apr 2026 22:42:18 +0900 Message-Id: Cc: "Miguel Ojeda" , "Boqun Feng" , "Gary Guo" , "Bjorn Roy Baron" , "Benno Lossin" , "Andreas Hindborg" , "Alice Ryhl" , "Trevor Gross" , "Danilo Krummrich" , "Dave Airlie" , "Daniel Almeida" , "Koen Koning" , , , "Nikola Djukic" , "Maarten Lankhorst" , "Maxime Ripard" , "Thomas Zimmermann" , "David Airlie" , "Simona Vetter" , "Jonathan Corbet" , "Alex Deucher" , "Christian Koenig" , "Jani Nikula" , "Joonas Lahtinen" , "Rodrigo Vivi" , "Tvrtko Ursulin" , "Huang Rui" , "Matthew Auld" , "Matthew Brost" , "Lucas De Marchi" , "Thomas Hellstrom" , "Helge Deller" , "Alex Gaynor" , "Boqun Feng" , "John Hubbard" , "Alistair Popple" , "Timur Tabi" , "Edwin Peer" , "Alexandre Courbot" , "Andrea Righi" , "Andy Ritger" , "Zhi Wang" , "Balbir Singh" , "Philipp Stanner" , "Elle Rhumsaa" , , , , , , , Subject: Re: [PATCH v10 12/21] gpu: nova-core: mm: Add unified page table entry wrapper enums From: "Eliot Courtney" To: "Joel Fernandes" , "Eliot Courtney" , X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260311004008.2208806-1-joelagnelf@nvidia.com> <20260331212048.2229260-1-joelagnelf@nvidia.com> <20260331212048.2229260-13-joelagnelf@nvidia.com> <5db2aab1-4b65-486e-ad9b-27a108bdb0d6@nvidia.com> In-Reply-To: <5db2aab1-4b65-486e-ad9b-27a108bdb0d6@nvidia.com> X-ClientProxiedBy: DUZPR01CA0005.eurprd01.prod.exchangelabs.com (2603:10a6:10:3c3::9) To BL0PR12MB2353.namprd12.prod.outlook.com (2603:10b6:207:4c::31) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL0PR12MB2353:EE_|CYXPR12MB9428:EE_ X-MS-Office365-Filtering-Correlation-Id: a437c496-13c8-45a9-88c0-08de94ab7fd9 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|10070799003|366016|1800799024|7416014|376014|56012099003|22082099003|18002099003; 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>>> + >>> + // PTE pages at the leaf level. >>> + let pte_epp =3D self.entries_per_page(self.pte_level()); >>> + let mut pages_at_level =3D num_virt_pages.div_ceil(pte_epp); >>> + total +=3D pages_at_level; >>> + >>> + // Walk PDE levels bottom-up (reverse of pde_levels()). >>> + for &level in self.pde_levels().iter().rev() { >>> + let epp =3D self.entries_per_page(level); >>> + >>> + // How many pages at this level do we need to point to >>> + // the previous pages_at_level? >>> + pages_at_level =3D pages_at_level.div_ceil(epp); >>> + total +=3D pages_at_level; >>> + } >>> + >>> + total >>> + } >>> +} >>> + >>=20 >> We have a lot of matches on the MMU version here (and below in Pte, Pde, >> DualPde). What about making MmuVersion into a trait (e.g. Mmu) with >> associated types for Pte, Pde, DualPde which can implement traits >> defining their common operations too? > > I coded this up and it did not look pretty, there's not much LOC savings = and the > code becomes harder to read because of parametrization of several functio= ns. Also: Thanks for looking into it. Sorry to be a bother, but would you have a branch around with the code? I'm curious what didn't look good about it. >> Then you can parameterise Vmm/PtWalk on this type. > > The match still to be done somewhere, so you end up matching on chipset t= o call > the correct parametrized functions versus just passing in the parameter o= r > chipset down, in some cases. > > For now I am inclined to leave it as is. Also there's a Rust pitfall we a= ll > learnt during the turing and other patch reviews, sometimes doing a bunch= of > matches is good especially if the number of variants are expected to be f= ixed > (in the mm case, version 2 and version 3). Traits have some disadvantages= too, > example dyn traits have to heap-allocated, parametrizing can increase cod= e size > (due to monomorphization) etc. Yeah, it's just this is a lot of matches in a lot of places. And we have ver2 / ver3 specific code leaking into the general pagetable.rs file. So it would be really nice if we could find a way to improve this specific aspect. We can reduce the match to happening in just one file. You can avoid heap allocation if you would like by making Vmm an enum, for example, and doing the match based dispatch there at the top of the API tree, rather than at the bottom where it fans out into a lot more locations. > > thanks, > > -- > Joel Fernandes