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Message-ID: <882a4ba5-b0ef-4c21-8167-e2949424912c@redhat.com>
Date: Mon, 10 Jun 2024 23:46:55 +0300
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Subject: Re: [PATCH v7 4/4] rust: add abstraction for `struct page`
To: Alice Ryhl <aliceryhl@google.com>, Miguel Ojeda <ojeda@kernel.org>,
 Matthew Wilcox <willy@infradead.org>, Al Viro <viro@zeniv.linux.org.uk>,
 Andrew Morton <akpm@linux-foundation.org>, Kees Cook <keescook@chromium.org>
Cc: Alex Gaynor <alex.gaynor@gmail.com>,
 Wedson Almeida Filho <wedsonaf@gmail.com>, Boqun Feng
 <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
 =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
 Benno Lossin <benno.lossin@proton.me>,
 Andreas Hindborg <a.hindborg@samsung.com>,
 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 =?UTF-8?Q?Arve_Hj=C3=B8nnev=C3=A5g?= <arve@android.com>,
 Todd Kjos <tkjos@android.com>, Martijn Coenen <maco@android.com>,
 Joel Fernandes <joel@joelfernandes.org>, Carlos Llamas
 <cmllamas@google.com>, Suren Baghdasaryan <surenb@google.com>,
 Arnd Bergmann <arnd@arndb.de>, Trevor Gross <tmgross@umich.edu>,
 linux-mm@kvack.org, linux-kernel@vger.kernel.org,
 rust-for-linux@vger.kernel.org, Christian Brauner <brauner@kernel.org>,
 Danilo Krummrich <dakr@redhat.com>
References: <20240528-alice-mm-v7-0-78222c31b8f4@google.com>
 <20240528-alice-mm-v7-4-78222c31b8f4@google.com>
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From: Abdiel Janulgue <abdiel@redhat.com>
In-Reply-To: <20240528-alice-mm-v7-4-78222c31b8f4@google.com>
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Hi,

On 28/05/2024 17:58, Alice Ryhl wrote:
> Adds a new struct called `Page` that wraps a pointer to `struct page`.
> This struct is assumed to hold ownership over the page, so that Rust
> code can allocate and manage pages directly.
> 
> +
> +impl Drop for Page {
> +    fn drop(&mut self) {
> +        // SAFETY: By the type invariants, we have ownership of the page and can free it.
> +        unsafe { bindings::__free_pages(self.page.as_ptr(), 0) };
> +    }
> +}
> 

What about cases where the struct page pointer is not owned or allocated 
by this wrapper? For example, pages returned vmalloc_to_page()?
Any thoughts about exposing a provision to avoid freeing those pages 
during Drop?

We've been experimenting in adapting this Page wrapper in advance for 
page management within the Nova DRM driver.

/Abdiel