Re: "mm: use early_pfn_to_nid in page_ext_init" broken on some configurations?

[Joonsoo Kim]

On Fri, Jun 30, 2017 at 05:44:16PM +0200, Michal Hocko wrote:
> On Fri 30-06-17 17:42:24, Michal Hocko wrote:
> [...]
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > index 16532fa0bb64..894697c1e6f5 100644
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -1055,6 +1055,7 @@ static inline struct zoneref 
> > *first_zones_zonelist(struct zonelist *zonelist,
> >     !defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP)
> >  static inline unsigned long early_pfn_to_nid(unsigned long pfn)
> >  {
> > +   BUILD_BUG_ON(!IS_ENABLED(CONFIG_NUMA));
> 
> Err, this should read BUILD_BUG_ON(IS_ENABLED(CONFIG_NUMA)) of course

Agreed.

However, AFAIK, ARM can set CONFIG_NUMA but it doesn't have
CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID and CONFIG_HAVE_MEMBLOCK_NODE_MAP.

If page_ext uses early_pfn_to_nid(), it will cause build error in ARM.

Therefore, I suggest following change.
CONFIG_DEFERRED_STRUCT_PAGE_INIT depends on proper early_pfn_to_nid().
So, following code will always work as long as
CONFIG_DEFERRED_STRUCT_PAGE_INIT works.

Thanks.

----------->8---------------
diff --git a/mm/page_ext.c b/mm/page_ext.c
index 88ccc044..e3db259 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -384,6 +384,7 @@ void __init page_ext_init(void)
 
        for_each_node_state(nid, N_MEMORY) {
                unsigned long start_pfn, end_pfn;
+               int page_nid;
 
                start_pfn = node_start_pfn(nid);
                end_pfn = node_end_pfn(nid);
@@ -405,8 +406,15 @@ void __init page_ext_init(void)
                         *
                         * Take into account DEFERRED_STRUCT_PAGE_INIT.
                         */
-                       if (early_pfn_to_nid(pfn) != nid)
+#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
+                       page_nid = early_pfn_to_nid(pfn);
+#else
+                       page_nid = pfn_to_nid(pfn);
+#endif
+
+                       if (page_nid != nid)
                                continue;
+
                        if (init_section_page_ext(pfn, nid))
                                goto oom;
                }