[PATCH 45/63] mm: numa: copy cpupid on page migration

[Mel Gorman]

From: Rik van Riel <riel@xxxxxxxxxx>

After page migration, the new page has the nidpid unset. This makes
every fault on a recently migrated page look like a first numa fault,
leading to another page migration.

Copying over the nidpid at page migration time should prevent erroneous
migrations of recently migrated pages.

Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
 mm/migrate.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/migrate.c b/mm/migrate.c
index 6ff845f..1e1dbc9 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -439,6 +439,8 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
  */
 void migrate_page_copy(struct page *newpage, struct page *page)
 {
+	int cpupid;
+
 	if (PageHuge(page) || PageTransHuge(page))
 		copy_huge_page(newpage, page);
 	else
@@ -475,6 +477,13 @@ void migrate_page_copy(struct page *newpage, struct page *page)
 			__set_page_dirty_nobuffers(newpage);
  	}
 
+	/*
+	 * Copy NUMA information to the new page, to prevent over-eager
+	 * future migrations of this same page.
+	 */
+	cpupid = page_cpupid_xchg_last(page, -1);
+	page_cpupid_xchg_last(newpage, cpupid);
+
 	mlock_migrate_page(newpage, page);
 	ksm_migrate_page(newpage, page);
 	/*
-- 
1.8.1.4

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