[PATCH] mm/page_alloc: Add some detailed comments in can_steal_fallback

From: Xiang Gao
Date: Fri Sep 20 2024 - 08:20:46 EST


From: gaoxiang17 <gaoxiang17@xxxxxxxxxx>

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

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0aefae4a26b2..8b0634d1728b 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;

+ /*
+ * movable pages won't cause permanent fragmentation, so when you alloc small pages,
+ * you just need to temporarily steal unmovable or reclaimable pages that are closest
+ * to the request size. After a while, memory compact may occur to form large contiguous
+ * pages, and the next movable allocation may not need to steal. Unmovable and reclaimable
+ * allocation need to actually steal pages.
+ */
if (order >= pageblock_order / 2 ||
start_mt == MIGRATE_RECLAIMABLE ||
start_mt == MIGRATE_UNMOVABLE ||
--
2.34.1