linux-kernel - [PATCH 5/6] mm: migrate: don't split THP for misplaced NUMA page

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Message-Id: <20210329183312.178266-6-shy828301@gmail.com>
Date:   Mon, 29 Mar 2021 11:33:11 -0700
From:   Yang Shi <shy828301@...il.com>
To:     mgorman@...e.de, kirill.shutemov@...ux.intel.com, ziy@...dia.com,
        mhocko@...e.com, ying.huang@...el.com, hughd@...gle.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: [PATCH 5/6] 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.

Signed-off-by: Yang Shi <shy828301@...il.com>
---
 mm/migrate.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 86325c750c14..1c0c873375ab 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1444,6 +1444,7 @@ 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);
 
 	if (!swapwrite)
 		current->flags |= PF_SWAPWRITE;
@@ -1495,7 +1496,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 			 */
 			case -ENOSYS:
 				/* THP migration is unsupported */
-				if (is_thp) {
+				if (is_thp && !nosplit) {
 					if (!try_split_thp(page, &page2, from)) {
 						nr_thp_split++;
 						goto retry;
-- 
2.26.2