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.
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?
>
>During online_pages phase, pgdat->nr_zones will be updated in case the
>zone is empty. Right now mem_hotplug_lock ensures that there is no
>contention during the update of nr_zones.
>
>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 protection of nr_zones.
>"
>
>Does that make sense?
>
>>
>> ---
>> v3:
>> * slightly modify the last paragraph of changelog based on Michal's
>> comment
>> v2:
>> * commit log changes
>> * modify the code in move_pfn_range_to_zone() instead of in
>> init_currently_empty_zone()
>> * pgdat_resize_lock documentation change
>> ---
>> include/linux/mmzone.h | 7 ++++---
>> mm/memory_hotplug.c | 5 ++---
>> 2 files changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index 3d0c472438d2..37d9c5c3faa6 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -635,9 +635,10 @@ typedef struct pglist_data {
>> #endif
>> #if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_DEFERRED_STRUCT_PAGE_INIT)
>> /*
>> - * Must be held any time you expect node_start_pfn, node_present_pages
>> - * or node_spanned_pages stay constant. Holding this will also
>> - * guarantee that any pfn_valid() stays that way.
>> + * Must be held any time you expect node_start_pfn,
>> + * node_present_pages, node_spanned_pages or nr_zones stay constant.
>> + * Holding this will also guarantee that any pfn_valid() stays that
>> + * way.
>> *
>> * pgdat_resize_lock() and pgdat_resize_unlock() are provided to
>> * manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 61972da38d93..f626e7e5f57b 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -742,14 +742,13 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
>> int nid = pgdat->node_id;
>> unsigned long 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);
>> + if (zone_is_empty(zone))
>> + init_currently_empty_zone(zone, start_pfn, nr_pages);
>> resize_zone_range(zone, start_pfn, nr_pages);
>> zone_span_writeunlock(zone);
>> resize_pgdat_range(pgdat, start_pfn, nr_pages);
>>
>
>
>--
>
>Thanks,
>
>David / dhildenb
--
Wei Yang
Help you, Help me
