On Mon 20-01-20 14:06:26, Michal Hocko wrote: > 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. OK, so I've double checked. do_move_page_to_node_array would carry the error code over to do_pages_move and it would store the status stored in the pm array. It contains page_to_nid(page) so the resulting code indeed behaves properly before my change and this is a regression. I have a very vague recollection that this has been brought up already. <...looks in notes...> Found it! The report is http://lkml.kernel.org/r/0329efa0984b9b0252ef166abb4498c0795fab36.1535113317.git.jstancek@xxxxxxxxxx and my proposed workaround was http://lkml.kernel.org/r/20180829145537.GZ10223@xxxxxxxxxxxxxx > 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. Sorry forgot to put a reference to the patch: http://lkml.kernel.org/r/20200119030636.11899-5-richardw.yang@xxxxxxxxxxxxxxx -- Michal Hocko SUSE Labs
