[PATCH] mm/page_alloc: Add some comments for specific scenarios to make it easier to understand why unmovable and reclaimable allocations can steal from moveable pageblocks by default.

[Xiang Gao <gxxa03070307@gmail.com>]

From: gaoxiang17 <gaoxiang17@xiaomi.com>

Signed-off-by: gaoxiang17 <gaoxiang17@xiaomi.com>
---
 mm/page_alloc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 91ace8ca97e2..cc8a7a0772cb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1818,6 +1818,13 @@ static bool can_steal_fallback(unsigned int order, int start_mt)
 	if (order >= pageblock_order)
 		return true;
 
+	/*
+	 * The reasons why unmovable and reclaimable allocations can steal from
+	 * moveable pageblocks by default aside from the above comments, a different
+	 * and better understood scenario is: System initializations are all movable
+	 * pageblocks. If you want to alloc unmovable and reclaimable pages,
+	 * you have to steal from moveable pageblocks or it may fail.
+	 */
 	if (order >= pageblock_order / 2 ||
 		start_mt == MIGRATE_RECLAIMABLE ||
 		start_mt == MIGRATE_UNMOVABLE ||
-- 
2.34.1