Re: [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings

[Alice Ryhl <aliceryhl@google.com>]

On Wed, Aug 13, 2025 at 03:35:41PM +0000, Burak Emir wrote:
> This series adds a Rust bitmap API for porting the approach from
> commit 15d9da3f818c ("binder: use bitmap for faster descriptor lookup")
> to Rust. The functionality in dbitmap.h makes use of bitmap and bitops.
> 
> The Rust bitmap API provides a safe abstraction to underlying bitmap
> and bitops operations. For now, only includes method necessary for
> dbitmap.h, more can be added later. We perform bounds checks for
> hardening, violations are programmer errors that result in panics.
> 
> We include set_bit_atomic and clear_bit_atomic operations. One has
> to avoid races with non-atomic operations, which is ensure by the
> Rust type system: either callers have shared references &bitmap in
> which case the mutations are atomic operations. Or there is a
> exclusive reference &mut bitmap, in which case there is no concurrent
> access.
> 
> This series includes an optimization to represent the bitmap inline,
> as suggested by Yury.
> 
> We ran a simple microbenchmark which shows that overall the Rust API 
> can be expected to be about 4.5% slower than C API.
> 
> We also introduce a Rust API in id_pool.rs that would replace 
> dbitmap.h from the commit referenced above. This data structure is coupled 
> with the bitmap API and adds support for growing and shrinking, along
> with fine-grained control over when allocation happens. 
> The Binder code needs this since it holds a spinlock at the time it
> discovers that growing is necessary; this has to be release
> for performing a memory allocation with GFP_KERNEL that may cause 
> sleep.  We include example doctests that demonstrate this usage.
> 
> Thanks everyone for all the helpful comments, this series has improved 
> significantly as a result of your work.

Thanks a lot for doing this, Burak! I gave it a spin locally on
v6.17-rc1, and it seems to work.

Alice