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

[Shivam Kalra via B4 Relay]

From: Shivam Kalra <shivamklr@xxxxxxx>

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@xxxxxxx>
---
 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);
+        }
     }
 
     pub(crate) fn set_manager_node(&self, node_ref: NodeRef) -> Result {

-- 
2.43.0