Re: [Qemu-devel] [PATCH v2 repost 6/7] mm: add the related functions to get free page info

[Michael S. Tsirkin]

On Thu, Jul 28, 2016 at 12:10:16AM +0000, Li, Liang Z wrote:
> > Subject: Re: [PATCH v2 repost 6/7] mm: add the related functions to get free
> > page info
> > 
> > On 07/26/2016 06:23 PM, Liang Li wrote:
> > > + for_each_migratetype_order(order, t) {
> > > +         list_for_each(curr, &zone->free_area[order].free_list[t]) {
> > > +                 pfn = page_to_pfn(list_entry(curr, struct page, lru));
> > > +                 if (pfn >= start_pfn && pfn <= end_pfn) {
> > > +                         page_num = 1UL << order;
> > > +                         if (pfn + page_num > end_pfn)
> > > +                                 page_num = end_pfn - pfn;
> > > +                         bitmap_set(bitmap, pfn - start_pfn,
> > page_num);
> > > +                 }
> > > +         }
> > > + }
> > 
> > Nit:  The 'page_num' nomenclature really confused me here.  It is the
> > number of bits being set in the bitmap.  Seems like calling it nr_pages or
> > num_pages would be more appropriate.
> > 
> 
> You are right,  will change.
> 
> > Isn't this bitmap out of date by the time it's send up to the hypervisor?  
> > Is
> > there something that makes the inaccuracy OK here?
> 
> Yes. The dirty page logging will be used to correct the inaccuracy.
> The dirty page logging should be started before getting the free page bitmap, 
> then if some of the free pages become no free for writing, these pages will 
> be tracked by the dirty page logging mechanism.
> 
> Thanks!
> Liang

Right but this should be clear from code and naming.