[Patch v3 4/4] mm/migrate.c: handle same node and add failure in the same way

[Wei Yang]

When page is not queued for migration, there are two possible cases:

  * page already on the target node
  * failed to add to migration queue

Current code handle them differently, this leads to a behavior
inconsistency.

Usually for each page's status, we just do store for once. While for the
page already on the target node, we might store the node information for
twice:

  * once when we found the page is on the target node
  * second when moving the pages to target node successfully after above
    action

The reason is even we don't add the page to pagelist, but store_status()
does store in a range which still contains the page.

This patch handles these two cases in the same way to reduce this
inconsistency and also make the code a little easier to read.

Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
---
 mm/migrate.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index b123ced445b7..bb4f45b120fd 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1665,18 +1665,18 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 		err = add_page_for_migration(mm, addr, current_node,
 				&pagelist, flags & MPOL_MF_MOVE_ALL);
 
-		if (!err) {
-			/* The page is already on the target node */
-			err = store_status(status, i, current_node, 1);
-			if (err)
-				goto out_flush;
-			continue;
-		} else if (err > 0) {
+		if (err > 0) {
 			/* The page is successfully queued for migration */
 			continue;
 		}
 
-		err = store_status(status, i, err, 1);
+		/*
+		 * Two possible cases for err here:
+		 * == 0: page is already on the target node, then store
+		 *       current_node to status
+		 * <  0: failed to add page to list, then store err to status
+		 */
+		err = store_status(status, i, err ? : current_node, 1);
 		if (err)
 			goto out_flush;
 
-- 
2.17.1