mm: migrate: do not retry 10 times for the subpages of fail-to-migrate THP

If THP is failed to migrate due to -ENOSYS or -ENOMEM case, the THP will
be split, and the subpages of fail-to-migrate THP will be tried to migrate
again, so we should not account the retry counter in the second loop,
since we already accounted 'nr_thp_failed' in the first loop.

Moreover we also do not need retry 10 times for -EAGAIN case for the
subpages of fail-to-migrate THP in the second loop, since we already
regarded the THP as migration failure, and save some migration time (for
the worst case, will try 512 * 10 times) according to previous discussion
[1].

[1] https://lore.kernel.org/linux-mm/[email protected]/

Link: https://lkml.kernel.org/r/[email protected]
Tested-by: "Huang, Ying" <[email protected]>
Signed-off-by: Baolin Wang <[email protected]>
Signed-off-by: "Huang, Ying" <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Zi Yan <[email protected]>
Cc: Yang Shi <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Baolin Wang

mm/migrate.c

@@ -1522,7 +1522,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 			case -EAGAIN:
 				if (is_thp)
 					thp_retry++;
-				else
+				else if (!no_subpage_counting)
 					retry++;
 				nr_retry_pages += nr_subpages;
 				break;
@@ -1548,8 +1548,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 			}
 		}
 	}
-	if (!no_subpage_counting)
-		nr_failed += retry;
+	nr_failed += retry;
 	nr_thp_failed += thp_retry;
 	nr_failed_pages += nr_retry_pages;
 	/*