Re: [PATCH 1/3] rust: maple_tree: add MapleTree

["Danilo Krummrich" <dakr@kernel.org>]

On Mon Jul 28, 2025 at 6:04 PM CEST, Boqun Feng wrote:
> On Sat, Jul 26, 2025 at 01:23:22PM +0000, Alice Ryhl wrote:
>> The maple tree will be used in the Tyr driver to allocate and keep track
>> of GPU allocations created internally (i.e. not by userspace). It will
>> likely also be used in the Nova driver eventually.
>> 
>> This adds the simplest methods for additional and removal that do not
>> require any special care with respect to concurrency.
>> 
>> This implementation is based on the RFC by Andrew but with significant
>> changes to simplify the implementation.
>> 
>> Co-developed-by: Andrew Ballance <andrewjballance@gmail.com>
>> Signed-off-by: Andrew Ballance <andrewjballance@gmail.com>
>> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
>> ---
> [...]
>> +    /// Free all `T` instances in this tree.
>> +    ///
>> +    /// # Safety
>> +    ///
>> +    /// This frees Rust data referenced by the maple tree without removing it from the maple tree.
>> +    /// The caller must ensure that no reference that remains in the maple tree is used incorrectly
>> +    /// after this call.
>> +    unsafe fn free_all_entries(self: Pin<&mut Self>) {
>> +        // SAFETY: The pointer references a valid maple tree.
>> +        let ma_state = unsafe { Opaque::new(bindings::MA_STATE(self.tree.get(), 0, usize::MAX)) };
>> +
>
> A meta comment here for the future direction: I think it really makes a
> lot of sense if we could have the Rust abstraction for struct ma_state,
> that'll allow us to have flexible locking strategy and Iterator-like
> interface. Maybe it's something Andrew can take a deeper look when
> MapleTree binding is in-tree (no word play intented ;-))?
>
> For example, with a ma_state binding, we can do:
>
>     let mas = MAState::new(self, 0..);
>
>     while let Some(v) = mas.next() {
>     	drop(v)
>     }

FYI: Left a similar comment on MapleLock [1]. :)

I'd rather have that sooner than later, free_all_entries() is a good internal
user.

[1] https://lore.kernel.org/all/DBNO0N1TDAGI.2OEWH6Y60JNYZ@kernel.org/