Commit b5bade97 authored by Baolin Wang's avatar Baolin Wang Committed by Linus Torvalds
Browse files

mm: migrate: fix the return value of migrate_pages() 

Patch series "Improve the migration stats".

According to talk with Zi Yan [1], this patch set changes the return
value of migrate_pages() to avoid returning a number which is larger
than the number of pages the users tried to migrate by move_pages()
syscall.  Also fix the hugetlb migration stats and migration stats in
trace_mm_compaction_migratepages().

[1] https://lore.kernel.org/linux-mm/7E44019D-2A5D-4BA7-B4D5-00D4712F1687@nvidia.com/

This patch (of 3):

As Zi Yan pointed out, the syscall move_pages() can return a
non-migrated number larger than the number of pages the users tried to
migrate, when a THP page is failed to migrate.  This is confusing for
users.

Since other migration scenarios do not care about the actual
non-migrated number of pages except the memory compaction migration
which will fix in following patch.  Thus we can change the return value
to return the number of {normal page, THP, hugetlb} instead to avoid
this issue, and the number of THP splits will be considered as the
number of non-migrated THP, no matter how many subpages of the THP are
migrated successfully.  Meanwhile we should still keep the migration
counters using the number of normal pages.

Link: https://lkml.kernel.org/r/cover.1636275127.git.baolin.wang@linux.alibaba.com
Link: https://lkml.kernel.org/r/6486fabc3e8c66ff613e150af25e89b3147977a6.1636275127.git.baolin.wang@linux.alibaba.com


Signed-off-by: default avatarBaolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: default avatarZi Yan <ziy@nvidia.com>
Co-developed-by: default avatarZi Yan <ziy@nvidia.com>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d6aba4c8

mm/migrate.c

+47 −16
Original line number Diff line number Diff line
@@ -1421,7 +1421,7 @@ static inline int try_split_thp(struct page *page, struct page **page2, 
 * @mode:		The migration mode that specifies the constraints for

 *			page migration, if any.

 * @reason:		The reason for page migration.

 * @ret_succeeded:	Set to the number of pages migrated successfully if

 * @ret_succeeded:	Set to the number of normal pages migrated successfully if

 *			the caller passes a non-NULL pointer.

 *

 * The function returns after 10 attempts or if no pages are movable any more
@@ -1429,7 +1429,9 @@ static inline int try_split_thp(struct page *page, struct page **page2, 
 * It is caller's responsibility to call putback_movable_pages() to return pages

 * to the LRU or free list only if ret != 0.

 *

 * Returns the number of pages that were not migrated, or an error code.

 * Returns the number of {normal page, THP} that were not migrated, or an error code.

 * The number of THP splits will be considered as the number of non-migrated THP,

 * no matter how many subpages of the THP are migrated successfully.

 */

int migrate_pages(struct list_head *from, new_page_t get_new_page,

		free_page_t put_new_page, unsigned long private,
@@ -1438,6 +1440,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, 
	int retry = 1;

	int thp_retry = 1;

	int nr_failed = 0;

	int nr_failed_pages = 0;

	int nr_succeeded = 0;

	int nr_thp_succeeded = 0;

	int nr_thp_failed = 0;
@@ -1449,13 +1452,16 @@ 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);

	LIST_HEAD(thp_split_pages);

	bool nosplit = (reason == MR_NUMA_MISPLACED);

	bool no_subpage_counting = false;



	trace_mm_migrate_pages_start(mode, reason);



	if (!swapwrite)

		current->flags |= PF_SWAPWRITE;



thp_subpage_migration:

	for (pass = 0; pass < 10 && (retry || thp_retry); pass++) {

		retry = 0;

		thp_retry = 0;
@@ -1504,18 +1510,20 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, 
			case -ENOSYS:

				/* THP migration is unsupported */

				if (is_thp) {

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

					nr_thp_failed++;

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

						nr_thp_split++;

						goto retry;

					}



					nr_thp_failed++;

					nr_failed += nr_subpages;

					nr_failed_pages += nr_subpages;

					break;

				}



				/* Hugetlb migration is unsupported */

				if (!no_subpage_counting)

					nr_failed++;

				nr_failed_pages++;

				break;

			case -ENOMEM:

				/*
@@ -1524,16 +1532,19 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, 
				 * THP NUMA faulting doesn't split THP to retry.

				 */

				if (is_thp && !nosplit) {

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

					nr_thp_failed++;

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

						nr_thp_split++;

						goto retry;

					}



					nr_thp_failed++;

					nr_failed += nr_subpages;

					nr_failed_pages += nr_subpages;

					goto out;

				}



				if (!no_subpage_counting)

					nr_failed++;

				nr_failed_pages++;

				goto out;

			case -EAGAIN:

				if (is_thp) {
@@ -1559,17 +1570,37 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, 
				 */

				if (is_thp) {

					nr_thp_failed++;

					nr_failed += nr_subpages;

					nr_failed_pages += nr_subpages;

					break;

				}



				if (!no_subpage_counting)

					nr_failed++;

				nr_failed_pages++;

				break;

			}

		}

	}

	nr_failed += retry + thp_retry;

	nr_failed += retry;

	nr_thp_failed += thp_retry;

	rc = nr_failed;

	/*

	 * Try to migrate subpages of fail-to-migrate THPs, no nr_failed

	 * counting in this round, since all subpages of a THP is counted

	 * as 1 failure in the first round.

	 */

	if (!list_empty(&thp_split_pages)) {

		/*

		 * Move non-migrated pages (after 10 retries) to ret_pages

		 * to avoid migrating them again.

		 */

		list_splice_init(from, &ret_pages);

		list_splice_init(&thp_split_pages, from);

		no_subpage_counting = true;

		retry = 1;

		goto thp_subpage_migration;

	}



	rc = nr_failed + nr_thp_failed;

out:

	/*

	 * Put the permanent failure page back to migration list, they
@@ -1578,11 +1609,11 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, 
	list_splice(&ret_pages, from);



	count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);

	count_vm_events(PGMIGRATE_FAIL, nr_failed);

	count_vm_events(PGMIGRATE_FAIL, nr_failed_pages);

	count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded);

	count_vm_events(THP_MIGRATION_FAIL, nr_thp_failed);

	count_vm_events(THP_MIGRATION_SPLIT, nr_thp_split);

	trace_mm_migrate_pages(nr_succeeded, nr_failed, nr_thp_succeeded,

	trace_mm_migrate_pages(nr_succeeded, nr_failed_pages, nr_thp_succeeded,

			       nr_thp_failed, nr_thp_split, mode, reason);



	if (!swapwrite)