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Subject[PATCH RFC 3/4] mm/page_alloc: always move pages to the tail of the freelist in unset_migratetype_isolate()
Date
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.

This change results in all pages getting onlined via online_pages() to
be placed to the tail of the freelist.

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 | 2 ++
mm/page_alloc.c | 36 +++++++++++++++++++++++++++++-----
mm/page_isolation.c | 8 ++++++--
3 files changed, 39 insertions(+), 7 deletions(-)

diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
index 572458016331..a36be2cf4dbb 100644
--- a/include/linux/page-isolation.h
+++ b/include/linux/page-isolation.h
@@ -38,6 +38,8 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
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_tail(struct zone *zone, struct page *page,
+ int migratetype);

/*
* 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 bba9a0f60c70..75b0f49b4022 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -899,6 +899,15 @@ 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)
{
@@ -2323,7 +2332,7 @@ static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
*/
static int move_freepages(struct zone *zone,
struct page *start_page, struct page *end_page,
- int migratetype, int *num_movable)
+ int migratetype, int *num_movable, bool to_tail)
{
struct page *page;
unsigned int order;
@@ -2354,7 +2363,10 @@ 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;
}
@@ -2362,8 +2374,9 @@ 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)
+static int __move_freepages_block(struct zone *zone, struct page *page,
+ int migratetype, int *num_movable,
+ bool to_tail)
{
unsigned long start_pfn, end_pfn;
struct page *start_page, *end_page;
@@ -2384,7 +2397,20 @@ int move_freepages_block(struct zone *zone, struct page *page,
return 0;

return move_freepages(zone, start_page, end_page, migratetype,
- num_movable);
+ num_movable, to_tail);
+}
+
+int move_freepages_block(struct zone *zone, struct page *page,
+ int migratetype, int *num_movable)
+{
+ return __move_freepages_block(zone, page, migratetype, num_movable,
+ false);
+}
+
+int move_freepages_block_tail(struct zone *zone, struct page *page,
+ int migratetype)
+{
+ return __move_freepages_block(zone, page, migratetype, NULL, true);
}

static void change_pageblock_range(struct page *pageblock_page,
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index abfe26ad59fd..84aa1d14751d 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -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 +106,13 @@ 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 freelists. This is especially relevant during
+ * memory onlining.
*/
if (!isolated_page) {
- nr_pages = move_freepages_block(zone, page, migratetype, NULL);
+ nr_pages = move_freepages_block_tail(zone, page, migratetype);
__mod_zone_freepage_state(zone, nr_pages, migratetype);
}
set_pageblock_migratetype(page, migratetype);
--
2.26.2
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