core/state/snapshot: reduce disk layer depth during generation

core/state/snapshot/snapshot.go

@@ -263,6 +263,13 @@ func (t *Tree) Cap(root common.Hash, layers int) error {
 	if !ok {
 		return fmt.Errorf("snapshot [%#x] is disk layer", root)
 	}
+	// If the generator is still running, use a more aggressive cap
+	diff.origin.lock.RLock()
+	if diff.origin.genMarker != nil && layers > 8 {
+		layers = 8
+	}
+	diff.origin.lock.RUnlock()
+
 	// Run the internal capping and discard all stale layers
 	t.lock.Lock()
 	defer t.lock.Unlock()