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

On 08/08/2017 02:12 PM, Wei Wang wrote:

On 08/03/2017 05:11 PM, Michal Hocko wrote:

quoted

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?

quoted

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.

quoted

            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