Whenever we move pages between freelists via move_to_free_list()/
move_freepages_block(), we don't actually touch the pages:
1. Page isolation doesn't actually touch the pages, it simply isolates
pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
When undoing isolation, we move the pages back to the target list.
2. Page stealing (steal_suitable_fallback()) moves free pages directly
between lists without touching them.
3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock() moves
free pages directly between freelists without touching them.
We already place pages to the tail of the freelists when undoing isolation
via __putback_isolated_page(), let's do it in any case (e.g., if order <=
pageblock_order) and document the behavior. To simplify, let's move the
pages to the tail for all move_to_free_list()/move_freepages_block() users.
In 2., the target list is empty, so there should be no change. In 3.,
we might observe a change, however, highatomic is more concerned about
allocations succeeding than cache hotness - if we ever realize this
change degrades a workload, we can special-case this instance and add a
proper comment.
This change results in all pages getting onlined via online_pages() to
be placed to the tail of the freelist.
Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
Acked-by: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>
Reviewed-by: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: Scott Cheloha <cheloha@xxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
mm/page_alloc.c | 10 +++++++---
mm/page_isolation.c | 5 +++++
2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index df5ff0cd6df1..b187e46cf640 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -901,13 +901,17 @@ static inline void add_to_free_list_tail(struct page *page, struct zone *zone,
area->nr_free++;
}
-/* Used for pages which are on another list */
+/*
+ * Used for pages which are on another list. Move the pages to the tail
+ * of the list - so the moved pages won't immediately be considered for
+ * allocation again (e.g., optimization for memory onlining).
+ */
static inline void move_to_free_list(struct page *page, struct zone *zone,
unsigned int order, int migratetype)
{
struct free_area *area = &zone->free_area[order];
- list_move(&page->lru, &area->free_list[migratetype]);
+ list_move_tail(&page->lru, &area->free_list[migratetype]);
}
static inline void del_page_from_free_list(struct page *page, struct zone *zone,
@@ -2340,7 +2344,7 @@ static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
#endif
/*
- * Move the free pages in a range to the free lists of the requested type.
+ * Move the free pages in a range to the freelist tail of the requested type.
* Note that start_page and end_pages are not aligned on a pageblock
* boundary. If alignment is required, use move_freepages_block()
*/
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index abfe26ad59fd..83692b937784 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -106,6 +106,11 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
* If we isolate freepage with more than pageblock_order, there
* should be no freepage in the range, so we could avoid costly
* pageblock scanning for freepage moving.
+ *
+ * We didn't actually touch any of the isolated pages, so place them
+ * to the tail of the freelist. This is an optimization for memory
+ * onlining - just onlined memory won't immediately be considered for
+ * allocation.
*/
if (!isolated_page) {
nr_pages = move_freepages_block(zone, page, migratetype, NULL);
--
2.26.2
