[PATCH v1 3/5] mm/page_alloc: always move pages to the tail of the freelist in unset_migratetype_isolate()

David Hildenbrand
2020-09-28T18:21:44Z

Page isolation doesn't actually touch the pages, it simply isolates
pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.

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.

Add a "to_tail" parameter to move_freepages_block() but introduce a
a new move_to_free_list_tail() - similar to add_to_free_list_tail().

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@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Scott Cheloha <cheloha@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
include/linux/page-isolation.h | 4 ++--
mm/page_alloc.c | 35 +++++++++++++++++++++++-----------
mm/page_isolation.c | 12 +++++++++---
3 files changed, 35 insertions(+), 16 deletions(-)

diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
index 572458016331..3eca9b3c5305 100644
--- a/include/linux/page-isolation.h
+++ b/include/linux/page-isolation.h
@@ -36,8 +36,8 @@ static inline bool is_migrate_isolate(int migratetype)
struct page *has_unmovable_pages(struct zone *zone, struct page *page,
int migratetype, int flags);
void set_pageblock_migratetype(struct page *page, int migratetype);
-int move_freepages_block(struct zone *zone, struct page *page,
- int migratetype, int *num_movable);
+int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
+ bool to_tail, int *num_movable);

/*
* Changes migrate type in [start_pfn, end_pfn) to be MIGRATE_ISOLATE.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9e3ed4a6f69a..d5a5f528b8ca 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -905,6 +905,15 @@ static inline void move_to_free_list(struct page *page, struct zone *zone,
list_move(&page->lru, &area->free_list[migratetype]);
}

+/* Used for pages which are on another list */
+static inline void move_to_free_list_tail(struct page *page, struct zone *zone,
+ unsigned int order, int migratetype)
+{
+ struct free_area *area = &zone->free_area[order];
+
+ list_move_tail(&page->lru, &area->free_list[migratetype]);
+}
+
static inline void del_page_from_free_list(struct page *page, struct zone *zone,
unsigned int order)
{
@@ -2338,9 +2347,9 @@ static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
* Note that start_page and end_pages are not aligned on a pageblock
* boundary. If alignment is required, use move_freepages_block()
*/
-static int move_freepages(struct zone *zone,
- struct page *start_page, struct page *end_page,
- int migratetype, int *num_movable)
+static int move_freepages(struct zone *zone, struct page *start_page,
+ struct page *end_page, int migratetype,
+ bool to_tail, int *num_movable)
{
struct page *page;
unsigned int order;
@@ -2371,7 +2380,10 @@ static int move_freepages(struct zone *zone,
VM_BUG_ON_PAGE(page_zone(page) != zone, page);

order = page_order(page);
- move_to_free_list(page, zone, order, migratetype);
+ if (to_tail)
+ move_to_free_list_tail(page, zone, order, migratetype);
+ else
+ move_to_free_list(page, zone, order, migratetype);
page += 1 << order;
pages_moved += 1 << order;
}
@@ -2379,8 +2391,8 @@ static int move_freepages(struct zone *zone,
return pages_moved;
}

-int move_freepages_block(struct zone *zone, struct page *page,
- int migratetype, int *num_movable)
+int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
+ bool to_tail, int *num_movable)
{
unsigned long start_pfn, end_pfn;
struct page *start_page, *end_page;
@@ -2401,7 +2413,7 @@ int move_freepages_block(struct zone *zone, struct page *page,
return 0;

return move_freepages(zone, start_page, end_page, migratetype,
- num_movable);
+ to_tail, num_movable);
}

static void change_pageblock_range(struct page *pageblock_page,
@@ -2526,8 +2538,8 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
if (!whole_block)
goto single_page;

- free_pages = move_freepages_block(zone, page, start_type,
- &movable_pages);
+ free_pages = move_freepages_block(zone, page, start_type, false,
+ &movable_pages);
/*
* Determine how many pages are compatible with our allocation.
* For movable allocation, it's the number of movable pages which
@@ -2635,7 +2647,8 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
&& !is_migrate_cma(mt)) {
zone->nr_reserved_highatomic += pageblock_nr_pages;
set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
- move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, NULL);
+ move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, false,
+ NULL);
}

out_unlock:
@@ -2711,7 +2724,7 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
*/
set_pageblock_migratetype(page, ac->migratetype);
ret = move_freepages_block(zone, page, ac->migratetype,
- NULL);
+ false, NULL);
if (ret) {
spin_unlock_irqrestore(&zone->lock, flags);
return ret;
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index abfe26ad59fd..de44e1329706 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -45,7 +45,7 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
set_pageblock_migratetype(page, MIGRATE_ISOLATE);
zone->nr_isolate_pageblock++;
nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE,
- NULL);
+ false, NULL);

__mod_zone_freepage_state(zone, -nr_pages, mt);
spin_unlock_irqrestore(&zone->lock, flags);
@@ -83,7 +83,7 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
* Because freepage with more than pageblock_order on isolated
* pageblock is restricted to merge due to freepage counting problem,
* it is possible that there is free buddy page.
- * move_freepages_block() doesn't care of merge so we need other
+ * move_freepages_block() don't care about merging, so we need another
* approach in order to merge them. Isolation and free will make
* these pages to be merged.
*/
@@ -106,9 +106,15 @@ 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);
+ nr_pages = move_freepages_block(zone, page, migratetype, true,
+ NULL);
__mod_zone_freepage_state(zone, nr_pages, migratetype);
}
set_pageblock_migratetype(page, migratetype);
--
2.26.2