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Subject[Patch v3 4/4] mm/migrate.c: handle same node and add failure in the same way
Date
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@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
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
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