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mm, hotplug: move init_currently_empty_zone() under zone_span_lock protection
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 locks (device_device_hotplug_lock and mem_hotplug_lock), which ensures there is no contention during the update of nr_zones. These global locks introduces scalability issues (especially the second one), which slow down code relying on get_online_mems(). This is also a preparation for not having to rely on get_online_mems() but instead some more fine grained locks. 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. Link: http://lkml.kernel.org/r/20181203205016.14123-1-richard.weiyang@gmail.com Signed-off-by: Wei Yang <richard.weiyang@gmail.com> Acked-by: Michal Hocko <mhocko@suse.com> Reviewed-by: Oscar Salvador <osalvador@suse.de> Cc: David Hildenbrand <david@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -636,8 +636,8 @@ typedef struct pglist_data {
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#endif
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#if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_DEFERRED_STRUCT_PAGE_INIT)
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/*
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* Must be held any time you expect node_start_pfn, node_present_pages
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* or node_spanned_pages stay constant.
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* Must be held any time you expect node_start_pfn,
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* node_present_pages, node_spanned_pages or nr_zones to stay constant.
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*
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* pgdat_resize_lock() and pgdat_resize_unlock() are provided to
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* manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG
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@ -743,14 +743,13 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
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int nid = pgdat->node_id;
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unsigned long flags;
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if (zone_is_empty(zone))
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init_currently_empty_zone(zone, start_pfn, nr_pages);
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clear_zone_contiguous(zone);
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/* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */
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pgdat_resize_lock(pgdat, &flags);
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zone_span_writelock(zone);
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if (zone_is_empty(zone))
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init_currently_empty_zone(zone, start_pfn, nr_pages);
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resize_zone_range(zone, start_pfn, nr_pages);
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zone_span_writeunlock(zone);
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resize_pgdat_range(pgdat, start_pfn, nr_pages);
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