On Mon, 13 May 2013 16:13:06 -0700 Cody P Schafer <c...@linux.vnet.ibm.com>
wrote:
> mmzone.h documents node_size_lock (which pgdat_resize_lock() locks) as
> follows:
>
> * Must be held any time you expect node_start_pfn, node_present_pages
> * or node_spanned_pages stay constant. [...]
Yeah, I suppose so. Although no present code sites actually do that.
> So actually hold it when we update node_present_pages in online_pages().
>
> ...
>
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -915,6 +915,7 @@ static void node_states_set_node(int node, struct
> memory_notify *arg)
>
> int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int
> online_type)
> {
> + unsigned long flags;
> unsigned long onlined_pages = 0;
> struct zone *zone;
> int need_zonelists_rebuild = 0;
> @@ -993,7 +994,11 @@ int __ref online_pages(unsigned long pfn, unsigned long
> nr_pages, int online_typ
>
> zone->managed_pages += onlined_pages;
> zone->present_pages += onlined_pages;
> +
> + pgdat_resize_lock(zone->zone_pgdat, &flags);
> zone->zone_pgdat->node_present_pages += onlined_pages;
> + pgdat_resize_unlock(zone->zone_pgdat, &flags);
> +
> if (onlined_pages) {
> node_states_set_node(zone_to_nid(zone), &arg);
> if (need_zonelists_rebuild)
afaict the only benefits of making this change are
a) so that code which does
a = p->node_present_pages;
...
b = p->node_present_pages;
can ensure that `a' and `b' are equal, by taking pgdat_resize_lock().
Which is somewhat odd, and
b) to make the comment truthful ;)
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