mm/page_alloc: avoid unneeded alike_pages calculation

When free_pages is 0, alike_pages is not used.  So alike_pages calculation
can be avoided by checking free_pages early to save cpu cycles.  Also fix
typo 'comparable'.  It should be 'compatible' here.

Link: https://lkml.kernel.org/r/20230801123723.2225543-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c

@@ -1833,6 +1833,10 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
 
 	free_pages = move_freepages_block(zone, page, start_type,
 						&movable_pages);
+	/* moving whole block can fail due to zone boundary conditions */
+	if (!free_pages)
+		goto single_page;
+
 	/*
 	 * Determine how many pages are compatible with our allocation.
 	 * For movable allocation, it's the number of movable pages which
@@ -1854,14 +1858,9 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
 		else
 			alike_pages = 0;
 	}
-
-	/* moving whole block can fail due to zone boundary conditions */
-	if (!free_pages)
-		goto single_page;
-
 	/*
 	 * If a sufficient number of pages in the block are either free or of
-	 * comparable migratability as our allocation, claim the whole block.
+	 * compatible migratability as our allocation, claim the whole block.
 	 */
 	if (free_pages + alike_pages >= (1 << (pageblock_order-1)) ||
 			page_group_by_mobility_disabled)