[PATCH v3] rust_binder: speed up get_node_debug_info using lower_bound iter

Finding the next node in the RBTree can be done more efficiently using
the cursor_lower_bound, as it reduces cost from O(n) to O(log n).

Reviewed-by: Alice Ryhl <[email protected]>
Link: https://github.com/Rust-for-Linux/linux/issues/1249
Suggested-by: Alice Ryhl <[email protected]>
Signed-off-by: Rafael Passos <[email protected]>
---

V1: https://lore.kernel.org/rust-for-linux/[email protected]/
Changes from V1:
    - remove the "if/else" block checking if the current>prt.
      The cursor_lower_bound function returns the "key" or the next larger.
      This is indeed better, my check was unnecessary.
    - add a comment about this fact before the cursor_lower_bound

V2: https://lore.kernel.org/rust-for-linux/[email protected]/
Changes from V2:
    - formatting fixes with rustfmt


 drivers/android/binder/process.rs | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/android/binder/process.rs b/drivers/android/binder/process.rs
index cdd1a9079726..b74c26f041bf 100644
--- a/drivers/android/binder/process.rs
+++ b/drivers/android/binder/process.rs
@@ -1174,11 +1174,10 @@ fn get_node_debug_info(&self, data: UserSlice) -> Result {
 
         {
             let inner = self.inner.lock();
-            for (node_ptr, node) in &inner.nodes {
-                if *node_ptr > ptr {
-                    node.populate_debug_info(&mut out, &inner);
-                    break;
-                }
+            // cursor_lower_bound retrieves the "key" passed or the next existing larger key
+            if let Some(cursor) = inner.nodes.cursor_lower_bound(&(ptr + 1)) {
+                let (_, node) = cursor.current();
+                node.populate_debug_info(&mut out, &inner);
             }
         }
 
-- 
2.55.0