[PATCH v3 1/4] mm: don't steal highatomic pageblock

[Minchan Kim]

In page freeing path, migratetype is racy so that a highorderatomic
page could free into non-highorderatomic free list. If that page
is allocated, VM can change the pageblock from higorderatomic to
something. In that case, highatomic pageblock accounting is broken
so it doesn't work(e.g., VM cannot reserve highorderatomic pageblocks
any more although it doesn't reach 1% limit).

So, this patch prohibits the changing from highatomic to other type.
It's no problem because MIGRATE_HIGHATOMIC is not listed in fallback
array so stealing will only happen due to unexpected races which is
really rare. Also, such prohibiting keeps highatomic pageblock more
longer so it would be better for highorderatomic page allocation.

Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
---
 mm/page_alloc.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 55ad0229ebf3..79853b258211 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2154,7 +2154,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
 
 		page = list_first_entry(&area->free_list[fallback_mt],
 						struct page, lru);
-		if (can_steal)
+		if (can_steal &&
+			get_pageblock_migratetype(page) != MIGRATE_HIGHATOMIC)
 			steal_suitable_fallback(zone, page, start_migratetype);
 
 		/* Remove the page from the freelists */
@@ -2555,7 +2556,8 @@ int __isolate_free_page(struct page *page, unsigned int order)
 		struct page *endpage = page + (1 << order) - 1;
 		for (; page < endpage; page += pageblock_nr_pages) {
 			int mt = get_pageblock_migratetype(page);
-			if (!is_migrate_isolate(mt) && !is_migrate_cma(mt))
+			if (!is_migrate_isolate(mt) && !is_migrate_cma(mt)
+				&& mt != MIGRATE_HIGHATOMIC)
 				set_pageblock_migratetype(page,
 							  MIGRATE_MOVABLE);
 		}
-- 
2.7.4