[PATCH -V2 2/2] migrate: convert migrate_pages() to use folios

[Huang Ying]

Quite straightforward, the page functions are converted to
corresponding folio functions.  Same for comments.

THP specific code are converted to be large folio.

Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
---
 mm/migrate.c | 210 +++++++++++++++++++++++++++------------------------
 1 file changed, 112 insertions(+), 98 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index eed8082664f2..8e4088aab27a 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1373,231 +1373,245 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 	return rc;
 }
 
-static inline int try_split_thp(struct page *page, struct list_head *split_pages)
+static inline int try_split_folio(struct folio *folio, struct list_head *split_folios)
 {
 	int rc;
 
-	lock_page(page);
-	rc = split_huge_page_to_list(page, split_pages);
-	unlock_page(page);
+	folio_lock(folio);
+	rc = split_folio_to_list(folio, split_folios);
+	folio_unlock(folio);
 	if (!rc)
-		list_move_tail(&page->lru, split_pages);
+		list_move_tail(&folio->lru, split_folios);
 
 	return rc;
 }
 
 /*
- * migrate_pages - migrate the pages specified in a list, to the free pages
+ * migrate_pages - migrate the folios specified in a list, to the free folios
  *		   supplied as the target for the page migration
  *
- * @from:		The list of pages to be migrated.
- * @get_new_page:	The function used to allocate free pages to be used
- *			as the target of the page migration.
- * @put_new_page:	The function used to free target pages if migration
+ * @from:		The list of folios to be migrated.
+ * @get_new_page:	The function used to allocate free folios to be used
+ *			as the target of the folio migration.
+ * @put_new_page:	The function used to free target folios if migration
  *			fails, or NULL if no special handling is necessary.
  * @private:		Private data to be passed on to get_new_page()
  * @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 normal pages migrated successfully if
+ *			folio migration, if any.
+ * @reason:		The reason for folio migration.
+ * @ret_succeeded:	Set to the number of folios migrated successfully if
  *			the caller passes a non-NULL pointer.
  *
- * The function returns after 10 attempts or if no pages are movable any more
- * because the list has become empty or no retryable pages exist any more.
- * It is caller's responsibility to call putback_movable_pages() to return pages
+ * The function returns after 10 attempts or if no folios are movable any more
+ * because the list has become empty or no retryable folios exist any more.
+ * It is caller's responsibility to call putback_movable_pages() to return folios
  * to the LRU or free list only if ret != 0.
  *
- * Returns the number of {normal page, THP, hugetlb} 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.
+ * Returns the number of {normal folio, large folio, hugetlb} that were not
+ * migrated, or an error code. The number of large folio splits will be
+ * considered as the number of non-migrated large folio, no matter how many
+ * split folios of the large folio 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,
 		enum migrate_mode mode, int reason, unsigned int *ret_succeeded)
 {
 	int retry = 1;
+	int large_retry = 1;
 	int thp_retry = 1;
 	int nr_failed = 0;
 	int nr_failed_pages = 0;
 	int nr_retry_pages = 0;
 	int nr_succeeded = 0;
 	int nr_thp_succeeded = 0;
+	int nr_large_failed = 0;
 	int nr_thp_failed = 0;
 	int nr_thp_split = 0;
 	int pass = 0;
+	bool is_large = false;
 	bool is_thp = false;
-	struct page *page;
-	struct page *page2;
-	int rc, nr_subpages;
-	LIST_HEAD(ret_pages);
-	LIST_HEAD(thp_split_pages);
+	struct folio *folio, *folio2;
+	int rc, nr_pages;
+	LIST_HEAD(ret_folios);
+	LIST_HEAD(split_folios);
 	bool nosplit = (reason == MR_NUMA_MISPLACED);
-	bool no_subpage_counting = false;
+	bool no_split_folio_counting = false;
 
 	trace_mm_migrate_pages_start(mode, reason);
 
-thp_subpage_migration:
-	for (pass = 0; pass < 10 && (retry || thp_retry); pass++) {
+split_folio_migration:
+	for (pass = 0; pass < 10 && (retry || large_retry); pass++) {
 		retry = 0;
+		large_retry = 0;
 		thp_retry = 0;
 		nr_retry_pages = 0;
 
-		list_for_each_entry_safe(page, page2, from, lru) {
+		list_for_each_entry_safe(folio, folio2, from, lru) {
 			/*
-			 * THP statistics is based on the source huge page.
-			 * Capture required information that might get lost
-			 * during migration.
+			 * Large folio statistics is based on the source large
+			 * folio. Capture required information that might get
+			 * lost during migration.
 			 */
-			is_thp = PageTransHuge(page) && !PageHuge(page);
-			nr_subpages = compound_nr(page);
+			is_large = folio_test_large(folio) && !folio_test_hugetlb(folio);
+			is_thp = is_large && folio_test_pmd_mappable(folio);
+			nr_pages = folio_nr_pages(folio);
 			cond_resched();
 
-			if (PageHuge(page))
+			if (folio_test_hugetlb(folio))
 				rc = unmap_and_move_huge_page(get_new_page,
-						put_new_page, private, page,
-						pass > 2, mode, reason,
-						&ret_pages);
+						put_new_page, private,
+						&folio->page, pass > 2, mode,
+						reason,
+						&ret_folios);
 			else
 				rc = unmap_and_move(get_new_page, put_new_page,
-						private, page_folio(page), pass > 2, mode,
-						reason, &ret_pages);
+						private, folio, pass > 2, mode,
+						reason, &ret_folios);
 			/*
 			 * The rules are:
-			 *	Success: non hugetlb page will be freed, hugetlb
-			 *		 page will be put back
+			 *	Success: non hugetlb folio will be freed, hugetlb
+			 *		 folio will be put back
 			 *	-EAGAIN: stay on the from list
 			 *	-ENOMEM: stay on the from list
 			 *	-ENOSYS: stay on the from list
-			 *	Other errno: put on ret_pages list then splice to
+			 *	Other errno: put on ret_folios list then splice to
 			 *		     from list
 			 */
 			switch(rc) {
 			/*
-			 * THP migration might be unsupported or the
-			 * allocation could've failed so we should
-			 * retry on the same page with the THP split
-			 * to base pages.
+			 * Large folio migration might be unsupported or
+			 * the allocation could've failed so we should retry
+			 * on the same folio with the large folio split
+			 * to normal folios.
 			 *
-			 * Sub-pages are put in thp_split_pages, and
+			 * Split folios are put in split_folios, and
 			 * we will migrate them after the rest of the
 			 * list is processed.
 			 */
 			case -ENOSYS:
-				/* THP migration is unsupported */
-				if (is_thp) {
-					nr_thp_failed++;
-					if (!try_split_thp(page, &thp_split_pages)) {
-						nr_thp_split++;
+				/* Large folio migration is unsupported */
+				if (is_large) {
+					nr_large_failed++;
+					nr_thp_failed += is_thp;
+					if (!try_split_folio(folio, &split_folios)) {
+						nr_thp_split += is_thp;
 						break;
 					}
 				/* Hugetlb migration is unsupported */
-				} else if (!no_subpage_counting) {
+				} else if (!no_split_folio_counting) {
 					nr_failed++;
 				}
 
-				nr_failed_pages += nr_subpages;
-				list_move_tail(&page->lru, &ret_pages);
+				nr_failed_pages += nr_pages;
+				list_move_tail(&folio->lru, &ret_folios);
 				break;
 			case -ENOMEM:
 				/*
 				 * When memory is low, don't bother to try to migrate
-				 * other pages, just exit.
+				 * other folios, just exit.
 				 */
-				if (is_thp) {
-					nr_thp_failed++;
-					/* THP NUMA faulting doesn't split THP to retry. */
+				if (is_large) {
+					nr_large_failed++;
+					nr_thp_failed += is_thp;
+					/* Large folio NUMA faulting doesn't split to retry. */
 					if (!nosplit) {
-						int ret = try_split_thp(page, &thp_split_pages);
+						int ret = try_split_folio(folio, &split_folios);
 
 						if (!ret) {
-							nr_thp_split++;
+							nr_thp_split += is_thp;
 							break;
 						} else if (reason == MR_LONGTERM_PIN &&
 							   ret == -EAGAIN) {
 							/*
-							 * Try again to split THP to mitigate
-							 * the failure of longterm pinning.
+							 * Try again to split large folio to
+							 * mitigate the failure of longterm pinning.
 							 */
-							thp_retry++;
-							nr_retry_pages += nr_subpages;
+							large_retry++;
+							thp_retry += is_thp;
+							nr_retry_pages += nr_pages;
 							break;
 						}
 					}
-				} else if (!no_subpage_counting) {
+				} else if (!no_split_folio_counting) {
 					nr_failed++;
 				}
 
-				nr_failed_pages += nr_subpages + nr_retry_pages;
+				nr_failed_pages += nr_pages + nr_retry_pages;
 				/*
-				 * There might be some subpages of fail-to-migrate THPs
-				 * left in thp_split_pages list. Move them back to migration
+				 * There might be some split folios of fail-to-migrate large
+				 * folios left in split_folios list. Move them back to migration
 				 * list so that they could be put back to the right list by
-				 * the caller otherwise the page refcnt will be leaked.
+				 * the caller otherwise the folio refcnt will be leaked.
 				 */
-				list_splice_init(&thp_split_pages, from);
+				list_splice_init(&split_folios, from);
 				/* nr_failed isn't updated for not used */
+				nr_large_failed += large_retry;
 				nr_thp_failed += thp_retry;
 				goto out;
 			case -EAGAIN:
-				if (is_thp)
-					thp_retry++;
-				else if (!no_subpage_counting)
+				if (is_large) {
+					large_retry++;
+					thp_retry += is_thp;
+				} else if (!no_split_folio_counting) {
 					retry++;
-				nr_retry_pages += nr_subpages;
+				}
+				nr_retry_pages += nr_pages;
 				break;
 			case MIGRATEPAGE_SUCCESS:
-				nr_succeeded += nr_subpages;
-				if (is_thp)
-					nr_thp_succeeded++;
+				nr_succeeded += nr_pages;
+				nr_thp_succeeded += is_thp;
 				break;
 			default:
 				/*
 				 * Permanent failure (-EBUSY, etc.):
-				 * unlike -EAGAIN case, the failed page is
-				 * removed from migration page list and not
+				 * unlike -EAGAIN case, the failed folio is
+				 * removed from migration folio list and not
 				 * retried in the next outer loop.
 				 */
-				if (is_thp)
-					nr_thp_failed++;
-				else if (!no_subpage_counting)
+				if (is_large) {
+					nr_large_failed++;
+					nr_thp_failed += is_thp;
+				} else if (!no_split_folio_counting) {
 					nr_failed++;
+				}
 
-				nr_failed_pages += nr_subpages;
+				nr_failed_pages += nr_pages;
 				break;
 			}
 		}
 	}
 	nr_failed += retry;
+	nr_large_failed += large_retry;
 	nr_thp_failed += thp_retry;
 	nr_failed_pages += nr_retry_pages;
 	/*
-	 * 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.
+	 * Try to migrate split folios of fail-to-migrate large folios, no
+	 * nr_failed counting in this round, since all split folios of a
+	 * large folio is counted as 1 failure in the first round.
 	 */
-	if (!list_empty(&thp_split_pages)) {
+	if (!list_empty(&split_folios)) {
 		/*
-		 * Move non-migrated pages (after 10 retries) to ret_pages
+		 * Move non-migrated folios (after 10 retries) to ret_folios
 		 * to avoid migrating them again.
 		 */
-		list_splice_init(from, &ret_pages);
-		list_splice_init(&thp_split_pages, from);
-		no_subpage_counting = true;
+		list_splice_init(from, &ret_folios);
+		list_splice_init(&split_folios, from);
+		no_split_folio_counting = true;
 		retry = 1;
-		goto thp_subpage_migration;
+		goto split_folio_migration;
 	}
 
-	rc = nr_failed + nr_thp_failed;
+	rc = nr_failed + nr_large_failed;
 out:
 	/*
-	 * Put the permanent failure page back to migration list, they
+	 * Put the permanent failure folio back to migration list, they
 	 * will be put back to the right list by the caller.
 	 */
-	list_splice(&ret_pages, from);
+	list_splice(&ret_folios, from);
 
 	/*
-	 * Return 0 in case all subpages of fail-to-migrate THPs are
-	 * migrated successfully.
+	 * Return 0 in case all split folios of fail-to-migrate large folios
+	 * are migrated successfully.
 	 */
 	if (list_empty(from))
 		rc = 0;
-- 
2.35.1