On Sat 18-01-20 13:26:43, Yang Shi wrote:
The do_move_pages_to_node() might return > 0 value, the number of pages that are not migrated, then the value will be returned to userspace directly. But, move_pages() syscall would just return 0 or errno. So, we need reset the return value to 0 for such case as what pre-v4.17 did.
The patch is wrong. migrate_pages returns the number of pages it _hasn't_ migrated or -errno. Yeah that semantic sucks but... So err != 0 is always an error. Except err > 0 doesn't really provide any useful information to the userspace. I cannot really remember what was the actual behavior before my rework because there were some gotchas hidden there.
If you want to fix this properly then you have to query node status of each page unmigrated when migrate_pages fails with > 0. This would be easier if the fix is done on the latest cleanup posted to the list which consolidates all do_move_pages_to_node and store_status calls to a single function.
Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move") Cc: Michal Hocko mhocko@suse.com Cc: Wei Yang richardw.yang@linux.intel.com Cc: stable@vger.kernel.org [4.17+] Signed-off-by: Yang Shi yang.shi@linux.alibaba.com
mm/migrate.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/mm/migrate.c b/mm/migrate.c index 86873b6..3e75432 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1659,8 +1659,11 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes, goto out_flush; err = do_move_pages_to_node(mm, &pagelist, current_node);
if (err)
if (err) {if (err > 0)err = 0; goto out;}-- 1.8.3.1