Re: [PATCH 2/2] rust_binder: use bitmap for allocation of handles

Alice Ryhl
2025-10-21T13:37:06Z

On Mon, Oct 20, 2025 at 05:06:26PM +0200, Burak Emir wrote:
> On Mon, Oct 20, 2025 at 3:33 PM Alice Ryhl <aliceryhl@google.com> wrote:
> >
> > To find an unused Binder handle, Rust Binder currently iterates the
> > red/black tree from the beginning until it finds a gap in the keys. This
> > is extremely slow.
> >
> > To improve the performance, add a bitmap that keeps track of which
> > indices are actually in use. This allows us to quickly find an unused
> > key in the red/black tree.
> >
> > This logic matches the approach used by C Binder. It was chosen
> > partially because it's the most memory efficient solution.
> >
> > Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> > ---
> > drivers/android/binder/process.rs | 110 +++++++++++++++++++++++++++++++-------
> > 1 file changed, 90 insertions(+), 20 deletions(-)
> >
> > diff --git a/drivers/android/binder/process.rs b/drivers/android/binder/process.rs
> > index f13a747e784c84a0fb09cbf47442712106eba07c..357ba1b577c73ad3f2b525a8573424420577e92d 100644
> > --- a/drivers/android/binder/process.rs
> > +++ b/drivers/android/binder/process.rs
> > @@ -16,6 +16,7 @@
> >
> > use kernel::{
> > bindings,
> > + bitmap::BitmapVec,
> > cred::Credential,
> > error::Error,
> > fs::file::{self, File},
> > @@ -367,6 +368,8 @@ impl ListItem<{Self::LIST_NODE}> for NodeRefInfo {
> > struct ProcessNodeRefs {
> > /// Used to look up nodes using the 32-bit id that this process knows it by.
> > by_handle: RBTree<u32, ListArc<NodeRefInfo, { NodeRefInfo::LIST_PROC }>>,
> > + /// Used to quickly find unused ids in `by_handle`.
> > + handle_present: BitmapVec,
>
> Are you going to delete rust/kernel/id_pool.rs, too?
>
> I have no opinion on whether having an abstraction vs inlining the
> functionality is worth it. I mean just in order to avoid id_pool.rs
> hanging around as dead code.

No I should be using it in Binder. I forgot to update the code to use
it.

Alice