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

[Daniel Kiper <dkiper@net-space.pl>]

On Mon, Mar 28, 2011 at 08:55:27AM -0700, Dave Hansen wrote:
> 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);

Yes, you are right. I am wrong. I will correct that. However, as I said
ealier I do not like ALIGN() in size context. For me ALIGN() is operation
on an address which aligns this address to specified boundary. That is
why I prefer use here open coded version (I agree that it is the same
to ALIGN()). I think that ROUND() macro would be better in size context.
However, I am not native english speaker and if I missed something correct
me, please.

> You might also want to consider some nicer units for those suckers.

What do you mind ??? I think that in that context PAGES_PER_SECTION
is quite good.

> 'start_paddr' is _much_ easier to grok than 'start', for instance.

OK.

Daniel

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