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.

Link: https://lkml.kernel.org/r/20210518200801.7413-6-shy828301@gmail.com
Signed-off-by: Yang Shi <shy828301@gmail.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/migrate.c

@@ -1423,6 +1423,7 @@ 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);
 
@@ -1494,8 +1495,9 @@ 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;