Re: [virtio-dev] Re: [PATCH v13 4/5] mm: support reporting free page blocks

[Wei Wang <wei.w.wang@intel.com>]

On 08/08/2017 02:12 PM, Wei Wang wrote:
> On 08/03/2017 05:11 PM, Michal Hocko wrote:
> > On Thu 03-08-17 14:38:18, Wei Wang wrote:
> > This is just too ugly and wrong actually. Never provide struct page
> > pointers outside of the zone->lock. What I've had in mind was to simply
> > walk free lists of the suitable order and call the callback for each 
> > one.
> > Something as simple as
> >
> >     for (i = 0; i < MAX_NR_ZONES; i++) {
> >         struct zone *zone = &pgdat->node_zones[i];
> >
> >         if (!populated_zone(zone))
> >             continue;
>
> Can we directly use for_each_populated_zone(zone) here?
>
>
> > spin_lock_irqsave(&zone->lock, flags);
> >         for (order = min_order; order < MAX_ORDER; ++order) {
>
>
> This appears to be covered by for_each_migratetype_order(order, mt) 
> below.
>
>
> >             struct free_area *free_area = &zone->free_area[order];
> >             enum migratetype mt;
> >             struct page *page;
> >
> >             if (!free_area->nr_pages)
> >                 continue;
> >
> >             for_each_migratetype_order(order, mt) {
> >                 list_for_each_entry(page,
> >                         &free_area->free_list[mt], lru) {
> >
> >                     pfn = page_to_pfn(page);
> >                     visit(opaque2, prn, 1<<order);
> >                 }
> >             }
> >         }
> >
> >         spin_unlock_irqrestore(&zone->lock, flags);
> >     }
> >
> > [...]
>
> What do you think if we further simply the above implementation like 
> this:
>
> for_each_populated_zone(zone) {
>                 for_each_migratetype_order_decend(1, order, mt) {

here it will be min_order (passed by the caller), instead of "1",
that is, for_each_migratetype_order_decend(min_order, order, mt)


> spin_lock_irqsave(&zone->lock, flags);
>                         list_for_each_entry(page,
> &zone->free_area[order].free_list[mt], lru) {
>                                 pfn = page_to_pfn(page);
>                                 visit(opaque1, pfn, 1 << order);
>                         }
>                         spin_unlock_irqrestore(&zone->lock, flags);
>                 }
>         }


Best,
Wei