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

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