fix recycler free stat report (#23159)

* fix recycler free stat report

* update comments for ewma window size

* one atomic update with aggregated local counter

* fix clippy integer arithmetic error

* move free calcs outside of loop

* fix integer arithmetic error

perf/src/recycler.rs

@@ -14,14 +14,19 @@ use {
 // cushion against *normal* variations in the workload while bounding the
 // number of redundant garbage collected objects after temporary bursts.
 const RECYCLER_SHRINK_SIZE: usize = 1024;
-// Lookback window for averaging number of garbage collected objects in terms
-// of number of allocations.
+
+// Lookback window for exponential moving averaging number of garbage collected
+// objects in terms of number of allocations. The half-life of the decaying
+// factor based on the window size defined below is 11356. This means a sample
+// of gc.size() that is 11356 allocations ago has half of the weight as the most
+// recent sample of gc.size() at current allocation.
 const RECYCLER_SHRINK_WINDOW: usize = 16384;
 
 #[derive(Debug, Default)]
 struct RecyclerStats {
     total: AtomicUsize,
     reuse: AtomicUsize,
+    freed: AtomicUsize,
     max_gc: AtomicUsize,
 }
 
@@ -148,6 +153,10 @@ impl<T: Default + Reset> RecyclerX<T> {
             if gc.len() > RECYCLER_SHRINK_SIZE
                 && self.size_factor.load(Ordering::Acquire) >= SIZE_FACTOR_AFTER_SHRINK
             {
+                self.stats.freed.fetch_add(
+                    gc.len().saturating_sub(RECYCLER_SHRINK_SIZE),
+                    Ordering::Relaxed,
+                );
                 for mut x in gc.drain(RECYCLER_SHRINK_SIZE..) {
                     x.set_recycler(Weak::default());
                 }
@@ -169,7 +178,7 @@ impl<T: Default + Reset> RecyclerX<T> {
         }
         let total = self.stats.total.load(Ordering::Relaxed);
         let reuse = self.stats.reuse.load(Ordering::Relaxed);
-        let freed = self.stats.total.fetch_add(1, Ordering::Relaxed);
+        let freed = self.stats.freed.load(Ordering::Relaxed);
         datapoint_debug!(
             "recycler",
             ("gc_len", len as i64, i64),