linux-kernel - [PATCH v3 4/4] rust: binder: shrink all

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Message-Id: <20260207-binder-shrink-vec-v3-v3-4-8ff388563427@cock.li>
Date: Sat, 07 Feb 2026 17:02:50 +0530
From: Shivam Kalra via B4 Relay <devnull+shivamklr.cock.li@...nel.org>
To: Danilo Krummrich <dakr@...nel.org>, 
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
 Vlastimil Babka <vbabka@...e.cz>, 
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
 Uladzislau Rezki <urezki@...il.com>, Miguel Ojeda <ojeda@...nel.org>, 
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
 Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>, 
 Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 Arve Hjønnevåg <arve@...roid.com>, 
 Todd Kjos <tkjos@...roid.com>, Christian Brauner <brauner@...nel.org>, 
 Carlos Llamas <cmllamas@...gle.com>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Shivam Kalra <shivamklr@...k.li>
Subject: [PATCH v3 4/4] rust: binder: shrink all_procs when deregistering
 processes

From: Shivam Kalra <shivamklr@...k.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@...k.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);
+        }
     }

     pub(crate) fn set_manager_node(&self, node_ref: NodeRef) -> Result {

-- 
2.43.0