diff --git a/src/runtime/mheap.go b/src/runtime/mheap.go
index 055dfee..47e3a33 100644
--- a/src/runtime/mheap.go
+++ b/src/runtime/mheap.go
@@ -107,6 +107,14 @@
 	// This is accessed atomically.
 	reclaimCredit uintptr
 
+	// scavengeCredit is spare credit for extra bytes scavenged.
+	// Since the scavenging mechanisms operate on spans, it may
+	// scavenge more than requested. Any spare pages released
+	// go to this credit pool.
+	//
+	// This is protected by the mheap lock.
+	scavengeCredit uintptr
+
 	// Malloc stats.
 	largealloc  uint64                  // bytes allocated for large objects
 	nlargealloc uint64                  // number of large object allocations
@@ -165,7 +173,7 @@
 	// simply blocking GC (by disabling preemption).
 	sweepArenas []arenaIdx
 
-	_ uint32 // ensure 64-bit alignment of central
+	// _ uint32 // ensure 64-bit alignment of central
 
 	// central free lists for small size classes.
 	// the padding makes sure that the mcentrals are
@@ -1349,6 +1357,14 @@
 // starting from the largest span and working down. It then takes those spans
 // and places them in scav. h must be locked.
 func (h *mheap) scavengeLargest(nbytes uintptr) {
+	// Use up scavenge credit if there's any available.
+	if nbytes > h.scavengeCredit {
+		nbytes -= h.scavengeCredit
+		h.scavengeCredit = 0
+	} else {
+		h.scavengeCredit -= nbytes
+		return
+	}
 	// Iterate over the treap backwards (from largest to smallest) scavenging spans
 	// until we've reached our quota of nbytes.
 	released := uintptr(0)
@@ -1377,6 +1393,10 @@
 		h.scav.insert(s)
 		released += r
 	}
+	// If we over-scavenged, turn that extra amount into credit.
+	if released > nbytes {
+		h.scavengeCredit += released - nbytes
+	}
 }
 
 // scavengeAll visits each node in the unscav treap and scavenges the