On Mon, Jan 20, 2020 at 02:17:44PM +0100, Michal Hocko wrote: >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 Thanks, I see the change. >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 Well, the above two links return 404. > >> 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 -- Wei Yang Help you, Help me
