linux-kernel - [v3 PATCH 5/7] mm: migrate: don't split THP for misplaced NUMA page

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Date:   Tue, 18 May 2021 13:07:59 -0700
From:   Yang Shi <shy828301@...il.com>
To:     mgorman@...e.de, kirill.shutemov@...ux.intel.com, ziy@...dia.com,
        ying.huang@...el.com, mhocko@...e.com, hughd@...gle.com,
        gerald.schaefer@...ux.ibm.com, hca@...ux.ibm.com,
        gor@...ux.ibm.com, borntraeger@...ibm.com,
        akpm@...ux-foundation.org
Cc:     shy828301@...il.com, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [v3 PATCH 5/7] mm: migrate: don't split THP for misplaced NUMA page

The old behavior didn't split THP if migration is failed due to lack of
memory on the target node.  But the THP migration does split THP, so keep
the old behavior for misplaced NUMA page migration.

Acked-by: Mel Gorman <mgorman@...e.de>
Signed-off-by: Yang Shi <shy828301@...il.com>
---
 mm/migrate.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 26f79f516100..035daaec1ca0 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1420,6 +1420,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 	int swapwrite = current->flags & PF_SWAPWRITE;
 	int rc, nr_subpages;
 	LIST_HEAD(ret_pages);
+	bool nosplit = (reason == MR_NUMA_MISPLACED);
 
 	trace_mm_migrate_pages_start(mode, reason);
 
@@ -1491,8 +1492,9 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 				/*
 				 * When memory is low, don't bother to try to migrate
 				 * other pages, just exit.
+				 * THP NUMA faulting doesn't split THP to retry.
 				 */
-				if (is_thp) {
+				if (is_thp && !nosplit) {
 					if (!try_split_thp(page, &page2, from)) {
 						nr_thp_split++;
 						goto retry;
-- 
2.26.2