mm, migrate: count pages failing all retries in vmstat and tracepoint

Migration tries up to 10 times to migrate pages that return -EAGAIN until
it gives up.  If some pages fail all retries, they are counted towards the
number of failed pages that migrate_pages() returns.  They should also be
counted in the /proc/vmstat pgmigrate_fail and in the mm_migrate_pages
tracepoint.

Signed-off-by: Vlastimil Babka <[email protected]>
Acked-by: David Rientjes <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: "Aneesh Kumar K.V" <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
Cc: Mel Gorman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/migrate.c

@@ -1169,7 +1169,8 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 			}
 		}
 	}
-	rc = nr_failed + retry;
+	nr_failed += retry;
+	rc = nr_failed;
 out:
 	if (nr_succeeded)
 		count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);