Re: [PATCH 4/6] Have x86_64 use add_active_range() and free_area_init_nodes

[Mel Gorman <mel@csn.ul.ie>]

On Thu, 31 Aug 2006, Mika Penttilä wrote:

> > > > static __init inline int srat_disabled(void)
> > > > @@ -166,7 +167,7 @@ static int hotadd_enough_memory(struct b
> > > >
> > > >        if (mem < 0)
> > > >                return 0;
> > > > -       allowed = (end_pfn - e820_hole_size(0, end_pfn)) * PAGE_SIZE;
> > > > +       allowed = (end_pfn - absent_pages_in_range(0, end_pfn)) * 
> > > > PAGE_SIZE;
> > > >        allowed = (allowed / 100) * hotadd_percent;
> > > >        if (allocated + mem > allowed) {
> > > >                unsigned long range;
> > > > @@ -238,7 +239,7 @@ static int reserve_hotadd(int node, unsi
> > > >        }
> > > >
> > > >        /* This check might be a bit too strict, but I'm keeping it for 
> > > > now. */
> > > > -       if (e820_hole_size(s_pfn, e_pfn) != e_pfn - s_pfn) {
> > > > +       if (absent_pages_in_range(s_pfn, e_pfn) != e_pfn - s_pfn) {
> > > >                printk(KERN_ERR "SRAT: Hotplug area has existing 
> > > > memory\n");
> > > >                return -1;
> > > >        }
> > > We really do want to to compare against the e820 map at it contains
> > > the memory that is really present (this info was blown away before
> > > acpi_numa) 
> >
> > The information used by absent_pages_in_range() should match what was
> > available to e820_hole_size().
> But it doesn't : all active ranges are removed before parsing srat. I think 
> we really need to check against e820 here.

What I see happening is this;

1. setup_arch calls e820_register_active_regions(0, 0, -1UL) so that all
   regions are registered as if they were on node 0 so e820_end_of_ram()
   gets the right value
2. remove_all_active_regions() is called to clear what was registered so
   that rediscovery with NUMA awareness happens
3. acpi_numa_init() is called. It parses the table and a little later
   calls acpi_numa_memory_affinity_init() for each range in the table so
   now we're into x86_64 code
4. acpi_numa_memory_affinity_init() basically deals an address range.
   Assuming the SRAT table is not broken, it calls
   e820_register_active_ranges() for that range. At this point, for the
   range of addresses, the active ranges are now registered
5. reserve_hotadd is called if the range is hotpluggable. It will fail if
   it finds that memory already exists there

So, when absent_pages_in_range() is being called by reserve_hotadd(), it 
should be using the same information that was available in e820. What am I 
missing?

--
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab