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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rlVzj-0000000ClgU-2tv5; Sat, 16 Mar 2024 15:30:47 +0000 Date: Sat, 16 Mar 2024 15:30:47 +0000 From: Matthew Wilcox To: Alice Ryhl Cc: Andreas Hindborg , akpm@linux-foundation.org, alex.gaynor@gmail.com, arnd@arndb.de, arve@android.com, benno.lossin@proton.me, bjorn3_gh@protonmail.com, boqun.feng@gmail.com, brauner@kernel.org, cmllamas@google.com, gary@garyguo.net, gregkh@linuxfoundation.org, joel@joelfernandes.org, keescook@chromium.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, maco@android.com, ojeda@kernel.org, rust-for-linux@vger.kernel.org, surenb@google.com, tkjos@android.com, viro@zeniv.linux.org.uk, wedsonaf@gmail.com Subject: Re: [PATCH v3 4/4] rust: add abstraction for `struct page` Message-ID: References: <20240311-alice-mm-v3-4-cdf7b3a2049c@google.com> <20240311105056.122734-1-aliceryhl@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240311105056.122734-1-aliceryhl@google.com> X-Rspamd-Queue-Id: 8B5AD180008 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 5c1kwsf3i6419e3fgzeuzggjm3mtsjdp X-HE-Tag: 1710603060-792249 X-HE-Meta: U2FsdGVkX18CPReO0FVD85wUUiNerOVhK5CZyZrKKiMU/ZLUFaAjH0G0jOLeanJImtMon6H1AtcEuBSue29s1XT2kLRU1/31MVvfJvXo+l+we/cgpJ1HAwI/TjscMs3srqnFLKnxFSzuZcbERbJCoB4f716jvScMJHaTzYX7wlgtM464JyEMrGct2YVWq0xtjAuYvugWhgD5Mga0wrDGOBHWYU2boNeOWbEKGwIN3W94Sa5wDcZEGobU9mnNm76VwpKnlHLcK0QDpHFxhCrwbSG1ZR0suUAe0XmAiABi7yT1RwlGLTbX8AHy2WBG7kD5az2y2Sotc4+OxJ6sAAkeJsJHn7JEQ9OyFVA6VlQgVQjz7iOyGqHNoBIG3FF2dgfp7mYTpWweGBBerNI0byXT4PHh1bZ8N2MWeiFgJufIi4fyjCYIddNP6q/iu7QlRsA8pWPBKQ+RaroHEKwXyhfPrlWdYaWsMNDUgijXX393Au83B80lU5BvqloBKAltLzKDJEoR541fX0Qqa2CuPVzJLdm6BiNNytFaYoLHFEsS3+kYz+wRbjrEbpqsUh0MZkgnoPwkrcMwAFJjsiLiONJBTBdt5MbAVyTkV2lbcXC0ZiEub4d71HVreXOjMz7uvlb9oQi5HLIU1FN9zxfipXCieufDzg/PtHIf5NZHJVqBymwTL8yU553UgZBL6vDGsWRTTBOdWRd6hXNAvEMNJ4z+pwL7OC8SW0w0/wj5OXiCNVJX+3DagB50URnx2T8Fdxhmigfm/qjr9VcFnI2o0LlNDiTgWN7vHzFGRop9wkpfQdZiLHbcKzxRXJN62Q2wzo8JsgNSGMJK9LXsY8VvdamsGn2QYyUrc1b4TMoSkasaxX3lJWg0IT7YQDcYrAMnumPrO4Yfq5aBofc5W3yQgBDn3MFISD1LAdhcAIRnPzN+wATyux7HECUxLnMTdNGfM0dQYMlbJdtm+zKvfDHsGMy KomEcKRA GP5cRas4ISYeXzXBumawPbvY/6569HEMR6vStVHKpSfQByLogWhGIE7Xlwrny2CxAv0wPcq/b5f0kts9kbPH5W4PqvADXpj4D+HxJTnBAmjvPcfZoxB3RHQKrdQjxFfxRiwRyXRZqW9w+cYIhSK3crWOC53gZ265rRHuRFOJDLdwRUojEusW7/WVG0RUSOBUWQFDWRlEa96ShwRMNRMLCG+fiSzzVxQovm33mhw4pMfKUcnE= 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 Mon, Mar 11, 2024 at 10:50:56AM +0000, Alice Ryhl wrote: > Alice Ryhl writes: > > +/// Flags for the "get free page" function that underlies all memory allocations. > > +pub mod flags { > > + pub type gfp_t = bindings::gfp_t; > > + > > + /// `GFP_KERNEL` is typical for kernel-internal allocations. The caller requires `ZONE_NORMAL` > > + /// or a lower zone for direct access but can direct reclaim. > > + pub const GFP_KERNEL: gfp_t = bindings::GFP_KERNEL; > > + /// `GFP_ZERO` returns a zeroed page on success. > > + pub const __GFP_ZERO: gfp_t = bindings::__GFP_ZERO; > > + /// `GFP_HIGHMEM` indicates that the allocated memory may be located in high memory. > > + pub const __GFP_HIGHMEM: gfp_t = bindings::__GFP_HIGHMEM; > > +} > > > > [...] > > > > +impl Page { > > + /// Allocates a new page. > > + pub fn alloc_page(gfp_flags: flags::gfp_t) -> Result { > > + // SAFETY: The specified order is zero and we want one page. > > + let page = unsafe { bindings::alloc_pages(gfp_flags, 0) }; > > + let page = NonNull::new(page).ok_or(AllocError)?; > > + // INVARIANT: We checked that the allocation succeeded. > > + Ok(Self { page }) > > + } > > Matthew Wilcox: You suggested on a previous version that I use gfp flags > here, or that I rename it to e.g. BinderPage to make it clear that this > is specific to the kind of pages that Binder needs. I think what you have here is good. > In this version I added some gfp flags, but I'm not actually sure that > the Page abstraction works for all combinations of gfp flags. For > example, I use kmap_local_page when accessing the page, but is that > correct if there's a user that doesn't pass GFP_HIGHMEM? Yes, kmap_local_page() works for non-highmem pages (it's essentially a no-op)