[Xen-devel] Re: [PATCH] xen/balloon: Memory hotplug support for Xen balloon driver

[Dave Hansen <dave@xxxxxxxxxxxxxxxxxx>]

On Mon, 2011-03-28 at 11:47 +0200, Daniel Kiper wrote:
> 
> +static enum bp_state reserve_additional_memory(long credit)
> +{
> +       int nid, rc;
> +       u64 start;
> +       unsigned long balloon_hotplug = credit;
> +
> +       start = PFN_PHYS(SECTION_ALIGN_UP(max_pfn));
> +       balloon_hotplug = (balloon_hotplug & PAGE_SECTION_MASK) + 
> PAGES_PER_SECTION;
> +       nid = memory_add_physaddr_to_nid(start); 

Is the 'balloon_hotplug' calculation correct?  I _think_ you're trying
to round up to the SECTION_SIZE_PAGES.  But, if 'credit' was already
section-aligned I think you'll unnecessarily round up to the next
SECTION_SIZE_PAGES boundary.  Should it just be:

        balloon_hotplug = ALIGN(balloon_hotplug, PAGES_PER_SECTION);

You might also want to consider some nicer units for those suckers.
'start_paddr' is _much_ easier to grok than 'start', for instance.

-- Dave


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