Re: [PATCH] mm/memory hotplug: print the last vmemmap region at the end of hot add memory

[Zhu Guihua]

On 06/10/2015 04:29 AM, Andrew Morton wrote:
> On Tue, 9 Jun 2015 11:41:28 +0800 Zhu Guihua <zhugh.fnst@xxxxxxxxxxxxxx> wrote:
>
> > > > --- a/mm/memory_hotplug.c
> > > > +++ b/mm/memory_hotplug.c
> > > > @@ -513,6 +513,7 @@ int __ref __add_pages(int nid, struct zone *zone, unsigned long phys_start_pfn,
> > > >    			break;
> > > >    		err = 0;
> > > >    	}
> > > > +	vmemmap_populate_print_last();
> > > >    
> > > >    	return err;
> > > >    }
> > > vmemmap_populate_print_last() is only available on x86_64, when
> > > CONFIG_SPARSEMEM_VMEMMAP=y.  Are you sure this won't break builds?
> > I tried this on i386 and on x86_64 when CONFIG_SPARSEMEM_VMEMMAP=n ,
> > it builds ok.
> With powerpc:
>
> akpm3:/usr/src/25> make allmodconfig
> akpm3:/usr/src/25> make mm/memory_hotplug.o
> akpm3:/usr/src/25> nm mm/memory_hotplug.o | grep vmemmap_populate_print_last
> 	U .vmemmap_populate_print_last
> akpm3:/usr/src/25> grep -r vmemmap_populate_print_last arch/powerpc
> akpm3:/usr/src/25>
>
> So I think that's going to break.
>
> I expect ia64 will break also, but I didn't investigate.
> .

There is
void __weak __meminit vmemmap_populate_print last(void)
in /mm/sparse.c, so I think this won't break builds.

And I found the function was invoked in void __init sparse_init(void) 
without
CONFIG_SPARSEMEM_VMEMMAP=y.

I also tried this on arm, it builds ok too.

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