On 01.12.18 01:27, Wei Yang wrote: > On Fri, Nov 30, 2018 at 10:30:22AM +0100, David Hildenbrand wrote: >> On 30.11.18 07:58, Wei Yang wrote: >>> During online_pages phase, pgdat->nr_zones will be updated in case this >>> zone is empty. >>> >>> Currently the online_pages phase is protected by the global lock >>> mem_hotplug_begin(), which ensures there is no contention during the >>> update of nr_zones. But this global lock introduces scalability issues. >>> >>> The patch moves init_currently_empty_zone under both zone_span_writelock >>> and pgdat_resize_lock because both the pgdat state is changed (nr_zones) >>> and the zone's start_pfn. Also this patch changes the documentation >>> of node_size_lock to include the protectioin of nr_zones. >> >> s/protectioin/protection/ >> >>> >>> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx> >>> Acked-by: Michal Hocko <mhocko@xxxxxxxx> >>> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx> >>> CC: David Hildenbrand <david@xxxxxxxxxx> >>> >>> --- >>> David, I may not catch you exact comment on the code or changelog. If I >>> missed, just let me know. >> >> I guess I would have rewritten it to something like the following >> >> " >> Currently the online_pages phase is protected by two global locks >> (device_device_hotplug_lock and mem_hotplug_lock). Especial the latter >> can result in scalability issues, as it will slow down code relying on >> get_online_mems(). Let's prepare code for not having to rely on >> get_online_mems() but instead some more fine grained locks. > > I am not sure why we specify get_online_mems() here. mem_hotplug_lock is > grabed in many places besides this one. In my mind, each place introduce > scalability issue, not only this one. mem_hotplug_lock is grabbed in write only when adding/removing/onlining/offlining memory and when adding/removing device memory. The read locker are the critical part for now. > > Or you want to say, the mem_hotplug_lock will introduce scalability > issue in two place: > > * hotplug process itself > * slab allocation process > > The second one is more critical. And this is what we try to address? Indeed, especially as the first usually (except device memory) also uses the device_hotplug_lock, I only consider the second one critical. Feel free to change this description to whatever you like. As I already stated scalability of adding/removing/onlining/offlining is not really an issue as of now (prove me wrong :) ). So I would not care about including such information in this patch. -- Thanks, David / dhildenb
