Re: [PATCH v4 00/10] Add Rust linked list for reference counted values

[Alice Ryhl]

On Tue, Aug 6, 2024 at 3:59 PM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote:
>
> This patchset contains a Rust implementation of a doubly-linked list for
> use with reference counted values. Linked lists are famously hard to
> implement in Rust [1] given the cyclic nature of the pointers, and
> indeed, this implementation uses unsafe to get around that.
>
> Linked lists aren't great for cache locality reasons, but it can be hard
> to avoid them for cases where you need data structures that don't
> allocate. Most linked lists in Binder are for collections where order
> matters (usually stacks or queues). There are also a few lists that are
> just collections, but linked lists are only used for this purpose in
> cases where the linked list is cold and performance isn't that
> important. The linked list is chosen over Vec in this case so that I
> don't have to worry about reducing the capacity of the vector. (Our
> red/black trees are a much better place to look for improving cache
> locality of collections in Rust Binder, and the upcoming xarray bindings
> would help with that.)
>
> Please see the Rust Binder RFC [2] for usage examples.
>
> The linked lists are used all over Rust Binder, but some pointers for
> where to look for examples:
>
> [PATCH RFC 04/20] rust_binder: add work lists
> Implements the work lists that store heterogeneous items. Uses the
> various macros a bunch.
>
> [PATCH RFC 10/20] rust_binder: add death notifications
> Uses the cursor. Also has objects with multiple prev/next pointer pairs.
>
> [PATCH RFC 15/20] rust_binder: add process freezing
> Uses the iterator with for loops.
>
> Link: https://rust-unofficial.github.io/too-many-lists/ [1]
> Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-0-08ba9197f637@xxxxxxxxxx/ [2]
> Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> ---
> Changes in v4:
> - Support several impl blocks inside `impl_list_item!`.
> - Link to v3: https://lore.kernel.org/r/20240723-linked-list-v3-0-89db92c7dbf4@xxxxxxxxxx

Oops, forgot to fill this out. Also addressed the other comments from Benno.

Alice