mm: migrate: correct the hugetlb migration stats

Correct the migration stats for hugetlb with using compound_nr() instead
of thp_nr_pages(), meanwhile change 'nr_failed_pages' to record the
number of normal pages failed to migrate, including THP and hugetlb, and
'nr_succeeded' will record the number of normal pages migrated
successfully.

[baolin.wang@linux.alibaba.com: fix docs, per Mike]
  Link: https://lkml.kernel.org/r/141bdfc6-f898-3cc3-f692-726c5f6cb74d@linux.alibaba.com

Link: https://lkml.kernel.org/r/71a4b6c22f208728fe8c78ad26375436c4ff9704.1636275127.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/vm/page_migration.rst

@@ -263,15 +263,15 @@ Monitoring Migration
 The following events (counters) can be used to monitor page migration.
 
 1. PGMIGRATE_SUCCESS: Normal page migration success. Each count means that a
-   page was migrated. If the page was a non-THP page, then this counter is
-   increased by one. If the page was a THP, then this counter is increased by
-   the number of THP subpages. For example, migration of a single 2MB THP that
-   has 4KB-size base pages (subpages) will cause this counter to increase by
-   512.
+   page was migrated. If the page was a non-THP and non-hugetlb page, then
+   this counter is increased by one. If the page was a THP or hugetlb, then
+   this counter is increased by the number of THP or hugetlb subpages.
+   For example, migration of a single 2MB THP that has 4KB-size base pages
+   (subpages) will cause this counter to increase by 512.
 
 2. PGMIGRATE_FAIL: Normal page migration failure. Same counting rules as for
    PGMIGRATE_SUCCESS, above: this will be increased by the number of subpages,
-   if it was a THP.
+   if it was a THP or hugetlb.
 
 3. THP_MIGRATION_SUCCESS: A THP was migrated without being split.
 

mm/migrate.c

@@ -1429,9 +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 {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.
+ * 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.
  */
 int migrate_pages(struct list_head *from, new_page_t get_new_page,
 		free_page_t put_new_page, unsigned long private,
@@ -1474,7 +1474,7 @@ retry:
 			 * during migration.
 			 */
 			is_thp = PageTransHuge(page) && !PageHuge(page);
-			nr_subpages = thp_nr_pages(page);
+			nr_subpages = compound_nr(page);
 			cond_resched();
 
 			if (PageHuge(page))
@@ -1523,7 +1523,7 @@ retry:
 				/* Hugetlb migration is unsupported */
 				if (!no_subpage_counting)
 					nr_failed++;
-				nr_failed_pages++;
+				nr_failed_pages += nr_subpages;
 				break;
 			case -ENOMEM:
 				/*
@@ -1544,7 +1544,7 @@ retry:
 
 				if (!no_subpage_counting)
 					nr_failed++;
-				nr_failed_pages++;
+				nr_failed_pages += nr_subpages;
 				goto out;
 			case -EAGAIN:
 				if (is_thp) {
@@ -1554,12 +1554,11 @@ retry:
 				retry++;
 				break;
 			case MIGRATEPAGE_SUCCESS:
+				nr_succeeded += nr_subpages;
 				if (is_thp) {
 					nr_thp_succeeded++;
-					nr_succeeded += nr_subpages;
 					break;
 				}
-				nr_succeeded++;
 				break;
 			default:
 				/*
@@ -1576,7 +1575,7 @@ retry:
 
 				if (!no_subpage_counting)
 					nr_failed++;
-				nr_failed_pages++;
+				nr_failed_pages += nr_subpages;
 				break;
 			}
 		}