Re: [PATCH v4 3/3] rust_binder: shrink all_procs when deregistering processes

[Alice Ryhl <aliceryhl@google.com>]

On Thu, Feb 12, 2026 at 01:47:09PM +0530, Shivam Kalra wrote:
> When a process is deregistered from the binder context, the all_procs
> vector may have significant unused capacity. Add logic to shrink the
> vector using a conservative strategy that prevents shrink-then-regrow
> oscillation.
> The shrinking strategy triggers when length drops below 1/4 of capacity,
> and shrinks to 1/2 of capacity rather than to the exact length. This
> provides hysteresis to avoid repeated reallocations when the process
> count fluctuates.
> 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.
> 
> Suggested-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in>
> ---
>  drivers/android/binder/context.rs | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/android/binder/context.rs b/drivers/android/binder/context.rs
> index 9cf437c025a20..399dab475728b 100644
> --- a/drivers/android/binder/context.rs
> +++ b/drivers/android/binder/context.rs
> @@ -94,6 +94,17 @@ 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 to avoid memory waste,
> +        // but use a conservative strategy to prevent shrink-then-regrow oscillation.
> +        // Only shrink when length drops below 1/4 of capacity, and shrink to 1/2 capacity.
> +        let len = manager.all_procs.len();
> +        let cap = manager.all_procs.capacity();
> +        if len < cap / 4 {
> +            // Shrink to half capacity. Ignore allocation failures since this is just an
> +            // optimization; the vector remains valid even if shrinking fails.
> +            let _ = manager.all_procs.shrink_to(cap / 2, GFP_KERNEL);

Not a big deal, but perhaps we should write len*2 here instead of cap/2?
That way, if the cap got way far away from the length, it would equalize
right away.

Alice