On Sat, Sep 15, 2012 at 4:14 AM, Andrew Morton <akpm@linux-foundation.org>wrote:

> On Fri, 14 Sep 2012 20:00:09 +0900
> Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> wrote:
>
> > > @@ -187,9 +184,10 @@ void register_page_bootmem_info_node(struct
> pglist_data *pgdat)
> > >     end_pfn = pfn + pgdat->node_spanned_pages;
> > >
> > >     /* register_section info */
> > > -   for (; pfn < end_pfn; pfn += PAGES_PER_SECTION)
> > > -           register_page_bootmem_info_section(pfn);
> > > -
> > > +   for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
> > > +           if (pfn_valid(pfn) && (pfn_to_nid(pfn) == node))
> >
> > I cannot judge whether your configuration is correct or not.
> > Thus if it is correct, I want a comment of why the node check is
> > needed. In usual configuration, a node does not span the other one.
> > So it is natural that "pfn_to_nid(pfn) is same as "pgdat->node_id".
> > Thus we may remove the node check in the future.
>
>

yup.  How does this look?
>

It looks fine to me. Some platforms can have this unusual  configuration,
not only in IA64.
And register_page_bootmem_info_section() is only called by
register_page_bootmem_info_node(),
so we can delete pfn_valid() check in register_page_bootmem_info_section()

Thanks
Xishi Qiu


> ---
> a/mm/memory_hotplug.c~memory-hotplug-fix-a-double-register-section-info-bug-fix
> +++ a/mm/memory_hotplug.c
> @@ -185,6 +185,12 @@ void register_page_bootmem_info_node(str
>
>         /* register_section info */
>         for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
> +               /*
> +                * Some platforms can assign the same pfn to multiple
> nodes - on
> +                * node0 as well as nodeN.  To avoid registering a pfn
> against
> +                * multiple nodes we check that this pfn does not already
> +                * reside in some other node.
> +                */
>                 if (pfn_valid(pfn) && (pfn_to_nid(pfn) == node))
>                         register_page_bootmem_info_section(pfn);
>         }
> _
>
>