Commit d532e2e5 authored by Yang Shi's avatar Yang Shi Committed by Linus Torvalds
Browse files

mm: migrate: return -ENOSYS if THP migration is unsupported 

In the current implementation unmap_and_move() would return -ENOMEM if THP
migration is unsupported, then the THP will be split.  If split is failed
just exit without trying to migrate other pages.  It doesn't make too much
sense since there may be enough free memory to migrate other pages and
there may be a lot base pages on the list.

Return -ENOSYS to make consistent with hugetlb.  And if THP split is
failed just skip and try other pages on the list.

Just skip the whole list and exit when free memory is really low.

Link: https://lkml.kernel.org/r/20201113205359.556831-6-shy828301@gmail.com


Signed-off-by: default avatarYang Shi <shy828301@gmail.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 236c32eb

mm/migrate.c

+46 −16
Original line number Diff line number Diff line
@@ -1171,7 +1171,7 @@ static int unmap_and_move(new_page_t get_new_page, 
	struct page *newpage = NULL;



	if (!thp_migration_supported() && PageTransHuge(page))

		return -ENOMEM;

		return -ENOSYS;



	if (page_count(page) == 1) {

		/* page was freed from under us. So we are done. */
@@ -1378,6 +1378,20 @@ out: 
	return rc;

}



static inline int try_split_thp(struct page *page, struct page **page2,

				struct list_head *from)

{

	int rc = 0;



	lock_page(page);

	rc = split_huge_page_to_list(page, from);

	unlock_page(page);

	if (!rc)

		list_safe_reset_next(page, *page2, lru);



	return rc;

}



/*

 * migrate_pages - migrate the pages specified in a list, to the free pages

 *		   supplied as the target for the page migration
@@ -1455,7 +1469,6 @@ retry: 
			 *		     from list

			 */

			switch(rc) {

			case -ENOMEM:

			/*

			 * THP migration might be unsupported or the

			 * allocation could've failed so we should
@@ -1467,12 +1480,29 @@ retry: 
			 * we encounter them after the rest of the list

			 * is processed.

			 */

			case -ENOSYS:

				/* THP migration is unsupported */

				if (is_thp) {

					lock_page(page);

					rc = split_huge_page_to_list(page, from);

					unlock_page(page);

					if (!rc) {

						list_safe_reset_next(page, page2, lru);

					if (!try_split_thp(page, &page2, from)) {

						nr_thp_split++;

						goto retry;

					}



					nr_thp_failed++;

					nr_failed += nr_subpages;

					break;

				}



				/* Hugetlb migration is unsupported */

				nr_failed++;

				break;

			case -ENOMEM:

				/*

				 * When memory is low, don't bother to try to migrate

				 * other pages, just exit.

				 */

				if (is_thp) {

					if (!try_split_thp(page, &page2, from)) {

						nr_thp_split++;

						goto retry;

					}
@@ -1500,7 +1530,7 @@ retry: 
				break;

			default:

				/*

				 * Permanent failure (-EBUSY, -ENOSYS, etc.):

				 * Permanent failure (-EBUSY, etc.):

				 * unlike -EAGAIN case, the failed page is

				 * removed from migration page list and not

				 * retried in the next outer loop.

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