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

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