Re: [PATCH v3 0/2] rust: page: Add support for existing struct page mappings

[Alice Ryhl <aliceryhl@google.com>]

On Wed, Nov 20, 2024 at 5:57 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Tue, Nov 19, 2024 at 01:24:01PM +0200, Abdiel Janulgue wrote:
> > This series aims to add support for pages that are not constructed by an
> > instance of the rust Page abstraction, for example those returned by
> > vmalloc_to_page() or virt_to_page().
> >
> > Changes sinve v3:
> > - Use the struct page's reference count to decide when to free the
> >   allocation (Alice Ryhl, Boqun Feng).
>
> Bleh, this is going to be "exciting".  We're in the middle of a multi-year
> project to remove refcounts from struct page.  The lifetime of a page
> will be controlled by the memdesc that it belongs to.  Some of those
> memdescs will have refcounts, but others will not.
>
> We don't have a fully formed destination yet, so I can't give you a
> definite answer to a lot of questions.  Obviously I don't want to hold
> up the Rust project in any way, but I need to know that what we're trying
> to do will be expressible in Rust.
>
> Can we avoid referring to a page's refcount?

I don't think this patch needs the refcount at all, and the previous
version did not expose it. This came out of the advice to use put_page
over free_page. Does this mean that we should switch to put_page but
not use get_page?

Alice