On Wed, Nov 21, 2018 at 08:15:49AM +0100, Michal Hocko wrote: >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... I took a look at that commit, seems I need some time to understand this TODO. :-) > >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); Just want to make sure, Oscar suggests to move the code here to protect this under zone_span_lock. If this the correct, I would spin a v2 and try to address the TODO. > resize_zone_range(zone, start_pfn, nr_pages); > zone_span_writeunlock(zone); >-- >Michal Hocko >SUSE Labs -- Wei Yang Help you, Help me
