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b=XkDBN/xE9oWPNlcrCWXL07yKd/x9NSSWASauXwWDSzb4WTZdnAB57Vh6B85+jYtoo JYVC7SG8PU8+GArm0KxVBQxtz4j1eevX38ETGcrwqK3W//JnpSDfKHwXtSP5g4RFq3 mijJyUqdJ/Cpk4RUJgPzIeVnaETtDqZLbS7Yh7Z0L8FObw1XmVrQE1YswZ2P4768vS W5OEMh7up/3lPEfDKQSSs6TcbWcpYnpzZ69e66itU2tFngXuT0Y9ECMx3J8c5yBjIk GYqnAgTNiR+03W586JJBsd/22vPQvCShdLhpPOtrjdD9xDKBZMWb/mU/qZVPLzb++i yVoj+iNRiK5sQ== Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Sun, 24 Aug 2025 15:18:24 +0200 Message-Id: From: "Danilo Krummrich" Subject: Re: [PATCH] rust: alloc: add missing trait item MIN_ALIGN to Cmalloc Cc: , , , , , , , , , , , , , , "Miguel Ojeda" To: "Alice Ryhl" References: <20250824120656.208978-1-dakr@kernel.org> In-Reply-To: X-Stat-Signature: i53nyx13kbm1xx8nq8yjbbzxtt4xya11 X-Rspam-User: X-Rspamd-Queue-Id: 7B158140009 X-Rspamd-Server: rspam05 X-HE-Tag: 1756041511-440099 X-HE-Meta: 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 jmMMDG36 rEFHEEX2m8BwJi8hei6Xim/wpPOiGoqYM4OyrK3ShOsn+zZ5n9bJhsxIsVTtusRFMQwUJjgpdDzEKV2TIV2Ggq0bENLvZRtfAXNtXXqBSyUxnXMhT+ewmarY3ZIKrIH2a+mHpXmlAhM4KZHDWVQspahv4HPxAmhJfUBfnF/bfA9wSo1hRVm3+3d8/lO5c5pqMTkOuljCSopghxva+Jlg0Y23xp6apfmsB30SOvAXOEu2lQMTRRcyZbJ2V8sUew3wTyKteH2o0TwjhP90Z51yBUsE9MGupng8dz5lNgLvcwDQ0ONXPRyEAtVlggfe4t0/jHen2gXnL2Sq9hwOWmpd1orK2vqOaiJiifIFSFe53TvHE30jyygBj4jzvKD7H/Vl9OHsNG6xMdTnnfwOjnZqrs0Hm3FuZ4PC/YATppVHEayvnk7w= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun Aug 24, 2025 at 3:04 PM CEST, Danilo Krummrich wrote: > On Sun Aug 24, 2025 at 2:36 PM CEST, Alice Ryhl wrote: >> On Sun, Aug 24, 2025 at 2:07=E2=80=AFPM Danilo Krummrich wrote: >>> + const MIN_ALIGN: usize =3D bindings::ARCH_KMALLOC_MINALIGN; >> >> Is this the right value for normal malloc? > > Heh! ARCH_KMALLOC_MINALIGN should be correct, because the Cmalloc impleme= ntation > should (ideally) enforce a minimum alignment of ARCH_KMALLOC_MINALIGN for > compatibility reasons. > > However, double checking the existing code, it doesn't. Hence, the correc= t value > must either be > > const MIN_ALIGN: usize =3D align_of::(); > > instead. Or, we have to actually enforce ARCH_KMALLOC_MINALIGN. > > Given that this fix is only for within the -rc cycles, i.e. we will remov= e > allocator_test.rs before the MIN_ALIGN stuff ever hits an actual release,= just > using align_of::() should be fine. Just for completeness, allocator_test.rs is also broken for the assumption = that Vmalloc allocated memory is always PAGE_SIZE aligned. Vmalloc::MIN_ALIGN, of course, does not report PAGE_SIZE in the case of allocator_test.rs being in charge, but it's an assumption that people might rightfully rely on in their (unsafe) code. In the end, just another argument for getting rid of allocator_test.rs. :)