buddy: for batch return, check for full batch before instead of after

This way we have a better chance to call the actual return at a more
suitable time, for example outside a lock.

src/buddy.h

@@ -817,6 +817,9 @@ BUDDYF(return_off_page)(struct buddy_returns *rets, struct buddy_off_page *page)
 	map = buddy->map;
 	CHECK_OBJ_NOTNULL(map, BUDDY_MAP_MAGIC);
 
+	if (rets->n == rets->space)
+		BUDDYF(return)(rets);
+
 	assert(rets->n < rets->space);
 
 	if (page->off < 0 ||
@@ -837,8 +840,6 @@ BUDDYF(return_off_page)(struct buddy_returns *rets, struct buddy_off_page *page)
 
 	*page = buddy_off_page_nil;
 
-	if (rets->n == rets->space)
-		BUDDYF(return)(rets);
 	return (1);
 }
 
@@ -868,6 +869,9 @@ BUDDYF(return_off_extent)(struct buddy_returns *rets,
 	map = buddy->map;
 	CHECK_OBJ_NOTNULL(map, BUDDY_MAP_MAGIC);
 
+	if (rets->n == rets->space)
+		BUDDYF(return)(rets);
+
 	assert(rets->n < rets->space);
 
 	if (extent->off < 0 ||
@@ -892,9 +896,6 @@ BUDDYF(return_off_extent)(struct buddy_returns *rets,
 
 	*extent = buddy_off_extent_nil;
 
-	if (rets->n == rets->space)
-		BUDDYF(return)(rets);
-
 	return (1);
 }
 
@@ -1052,6 +1053,7 @@ BUDDYF(return1_ ## what)(buddy_t *buddy, struct buddy_ ## what *ret) \
 	struct buddy_returns *rets = BUDDY_RETURNS_STK(buddy, 1);	\
 									\
 	AN(BUDDYF(return_ ## what)(rets, ret));				\
+	BUDDYF(return)(rets);						\
 }
 
 // XXX remove off interface for !FREEPAGE_WHEN