linux-kernel - Re: [PATCH 3/3] rust: add abstraction for `struct page`

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Date: Tue, 30 Jan 2024 10:06:09 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Andreas Hindborg <a.hindborg@...sung.com>
Cc: Matthew Wilcox <willy@...radead.org>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Wedson Almeida Filho <wedsonaf@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Kees Cook <keescook@...omium.org>, 
	Al Viro <viro@...iv.linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Arve Hjønnevåg <arve@...roid.com>, 
	Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>, 
	Joel Fernandes <joel@...lfernandes.org>, Carlos Llamas <cmllamas@...gle.com>, 
	Suren Baghdasaryan <surenb@...gle.com>, Arnd Bergmann <arnd@...db.de>, 
	"linux-mm@...ck.org" <linux-mm@...ck.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"rust-for-linux@...r.kernel.org" <rust-for-linux@...r.kernel.org>, Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH 3/3] rust: add abstraction for `struct page`

On Tue, Jan 30, 2024 at 10:02 AM Andreas Hindborg
<a.hindborg@...sung.com> wrote:
>
>
> Matthew Wilcox <willy@...radead.org> writes:
>
> > On Wed, Jan 24, 2024 at 11:20:23AM +0000, Alice Ryhl wrote:
> >> +impl Page {
> >> +    /// Allocates a new set of contiguous pages.
> >> +    pub fn new() -> Result<Self, AllocError> {
> >> +        // SAFETY: These are the correct arguments to allocate a single page.
> >> +        let page = unsafe {
> >> +            bindings::alloc_pages(
> >> +                bindings::GFP_KERNEL | bindings::__GFP_ZERO | bindings::__GFP_HIGHMEM,
> >> +                0,
> >> +            )
> >> +        };
> >
> > This feels too Binder-specific to be 'Page'.  Pages are not necessarily
> > allocated with GFP_HIGHMEM, nor are they necessarily zeroed.  Maybe you
> > want a BinderPage type?
>
> Rust null block uses the same definition of these flags [1], so there is
> at least that synergy.
>
> I feel like we had the discussion of the flags before, although I can't
> find the thread now. I think the conclusion was that we fix them until
> we have code that need to actually change them (as to not add dead
> code).

I don't think there's any problem with replacing the constructor with
one that takes a flag argument dead-code-wise. I can definitely do
that.

Alice