[RFC PATCH 3/3] mm, page_alloc: prevent merge freepages between highatomic and others

[Wenwei Tao]

From: Wenwei Tao <ww.tao0320@xxxxxxxxx>

We might not want other migrate types pin highatomic pageblock
away since it's reserved for high order use. And also we might
not want reserve high atomic pages out of limit, we can add
check in __free_one_page but this might be costly, so just stop
the merging.

Signed-off-by: Wenwei Tao <ww.tao0320@xxxxxxxxx>
---
 mm/page_alloc.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b72b771..ffce9b5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -832,7 +832,8 @@ continue_merging:
 		 * We don't want to hit this code for the more frequent
 		 * low-order merging.
 		 */
-		if (unlikely(has_isolate_pageblock(zone))) {
+		if (unlikely(has_isolate_pageblock(zone) ||
+				zone->nr_reserved_highatomic)) {
 			int buddy_mt;
 
 			buddy_idx = __find_buddy_index(page_idx, order);
@@ -841,7 +842,9 @@ continue_merging:
 
 			if (migratetype != buddy_mt
 					&& (is_migrate_isolate(migratetype) ||
-						is_migrate_isolate(buddy_mt)))
+					is_migrate_isolate(buddy_mt) ||
+					migratetype == MIGRATE_HIGHATOMIC ||
+					buddy_mt == MIGRATE_HIGHATOMIC))
 				goto done_merging;
 		}
 		max_order++;
-- 
1.8.3.1