Re: [PATCH v3 4/4] rust: binder: shrink all_procs when deregistering processes

[Alice Ryhl <aliceryhl@google.com>]

On Sat, Feb 07, 2026 at 05:02:50PM +0530, Shivam Kalra via B4 Relay wrote:
> [PATCH v3 4/4] rust: binder: shrink all_procs when deregistering

The usual prefix for Rust Binder changes is rust_binder:, not
rust: binder:.

> From: Shivam Kalra <shivamklr@cock.li>
> 
> When a process is deregistered from the binder context, the all_procs
> vector may have significant unused capacity. Add logic to shrink the
> vector when capacity exceeds 128 and usage drops below 50%, reducing
> memory overhead for long-running systems.
> 
> The shrink operation uses GFP_KERNEL and is allowed to fail gracefully
> since it is purely an optimization. The vector remains valid and
> functional even if shrinking fails.
> 
> Signed-off-by: Shivam Kalra <shivamklr@cock.li>
> ---
>  drivers/android/binder/context.rs | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/android/binder/context.rs b/drivers/android/binder/context.rs
> index 9cf437c025a20..f2505fbf17403 100644
> --- a/drivers/android/binder/context.rs
> +++ b/drivers/android/binder/context.rs
> @@ -94,6 +94,16 @@ pub(crate) fn deregister_process(self: &Arc<Self>, proc: &Arc<Process>) {
>          }
>          let mut manager = self.manager.lock();
>          manager.all_procs.retain(|p| !Arc::ptr_eq(p, proc));
> +
> +        // Shrink the vector if it has significant unused capacity.
> +        // Only shrink if capacity > 128 to avoid repeated reallocations for small vectors.
> +        let len = manager.all_procs.len();
> +        let cap = manager.all_procs.capacity();
> +        if cap > 128 && len < cap / 2 {
> +            // Shrink to current length. Ignore allocation failures since this is just an
> +            // optimization; the vector remains valid even if shrinking fails.
> +            let _ = manager.all_procs.shrink_to(len, GFP_KERNEL);

Hmm. This way we need to reallocate immediately if one more process is
added. How about:

if len < cap / 4 {
    shrink_to(cap / 2);
}

Alice