On Wed 21-11-18 02:52:31, Wei Yang wrote: > On Tue, Nov 20, 2018 at 08:58:11AM +0100, osalvador@xxxxxxx wrote: > >> On the other hand I would like to see the global lock to go away because > >> it causes scalability issues and I would like to change it to a range > >> lock. This would make this race possible. > >> > >> That being said this is more of a preparatory work than a fix. One could > >> argue that pgdat resize lock is abused here but I am not convinced a > >> dedicated lock is much better. We do take this lock already and spanning > >> its scope seems reasonable. An update to the documentation is due. > > > >Would not make more sense to move it within the pgdat lock > >in move_pfn_range_to_zone? > >The call from free_area_init_core is safe as we are single-thread there. > > > > Agree. This would be better. > > >And if we want to move towards a range locking, I even think it would be more > >consistent if we move it within the zone's span lock (which is already > >wrapped with a pgdat lock). > > > > I lost a little here, just want to confirm with you. > > Instead of call pgdat_resize_lock() around init_currently_empty_zone() > in move_pfn_range_to_zone(), we move init_currently_empty_zone() before > resize_zone_range()? > > This sounds reasonable. Btw. resolving the existing TODO would be nice as well, now that you are looking that direction... diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index c6c42a7425e5..c75fca900044 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -743,13 +743,12 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn, int nid = pgdat->node_id; unsigned long flags; + /* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */ + pgdat_resize_lock(pgdat, &flags); if (zone_is_empty(zone)) init_currently_empty_zone(zone, start_pfn, nr_pages); clear_zone_contiguous(zone); - - /* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */ - pgdat_resize_lock(pgdat, &flags); zone_span_writelock(zone); resize_zone_range(zone, start_pfn, nr_pages); zone_span_writeunlock(zone); -- Michal Hocko SUSE Labs
