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

[Wei Wang]

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) {
                        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