linux-kernel - [PATCH v5 4/9] mm/migrate: clear __GFP_RECLAIM to make the migration callback consistent with regular THP allocations

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Date:   Mon, 13 Jul 2020 15:41:52 +0900
From:   js1304@...il.com
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@....com, Vlastimil Babka <vbabka@...e.cz>,
        Christoph Hellwig <hch@...radead.org>,
        Roman Gushchin <guro@...com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Michal Hocko <mhocko@...e.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: [PATCH v5 4/9] mm/migrate: clear __GFP_RECLAIM to make the migration callback consistent with regular THP allocations

From: Joonsoo Kim <iamjoonsoo.kim@....com>

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.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
---
 mm/migrate.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/migrate.c b/mm/migrate.c
index 3b3d918..1cfc965 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1547,6 +1547,11 @@ struct page *new_page_nodemask(struct page *page,
 	}

 	if (PageTransHuge(page)) {
+		/*
+		 * clear __GFP_RECALIM to make the migration callback
+		 * consistent with regular THP allocations.
+		 */
+		gfp_mask &= ~__GFP_RECLAIM;
 		gfp_mask |= GFP_TRANSHUGE;
 		order = HPAGE_PMD_ORDER;
 	}
-- 
2.7.4