[134/165] mm/migrate: clear __GFP_RECLAIM to make the migration callback consistent with regular THP allocations

Commit Message

Andrew Morton Aug. 12, 2020, 1:37 a.m. UTC

From: Joonsoo Kim <[e-mail]>
Subject: mm/migrate: clear __GFP_RECLAIM to make the migration callback consistent with regular THP allocations

new_page_nodemask is a migration callback and it tries to use a common gfp
flags for the target page allocation whether it is a base page or a THP. 
The later only adds GFP_TRANSHUGE to the given mask.  This results in the
allocation being slightly more aggressive than necessary because the
resulting gfp mask will contain also __GFP_RECLAIM_KSWAPD.  THP
allocations usually exclude this flag to reduce over eager background
reclaim during a high THP allocation load which has been seen during large
mmaps initialization.  There is no indication that this is a problem for
migration as well but theoretically the same might happen when migrating
large mappings to a different node.  Make the migration callback
consistent with regular THP allocations.

[[e-mail]: fix comment typo, per Vlastimil]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Joonsoo Kim <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Mike Kravetz <[e-mail]>
Cc: Naoya Horiguchi <[e-mail]>
Cc: Roman Gushchin <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/migrate.c |    5 +++++
 1 file changed, 5 insertions(+)

Patch

--- a/mm/migrate.c~mm-migrate-clear-__gfp_reclaim-to-make-the-migration-callback-consistent-with-regular-thp-allocations
+++ a/mm/migrate.c
@@ -1554,6 +1554,11 @@  struct page *new_page_nodemask(struct pa
 	}
 
 	if (PageTransHuge(page)) {
+		/*
+		 * clear __GFP_RECLAIM to make the migration callback
+		 * consistent with regular THP allocations.
+		 */
+		gfp_mask &= ~__GFP_RECLAIM;
 		gfp_mask |= GFP_TRANSHUGE;
 		order = HPAGE_PMD_ORDER;
 	}