On Mon, Dec 03, 2018 at 11:09:52AM +0100, David Hildenbrand wrote: >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 for your information. Let me try to reword the changelog. >-- > >Thanks, > >David / dhildenb -- Wei Yang Help you, Help me
