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Subject: Re: [PATCH v15 4/5] mm: support reporting free page blocks
On 08/28/2017 09:33 PM, Michal Hocko wrote:
On Mon 28-08-17 18:08:32, Wei Wang wrote:This patch adds support to walk through the free page blocks in the system and report them via a callback function. Some page blocks may leave the free list after zone->lock is released, so it is the caller's responsibility to either detect or prevent the use of such pages. One use example of this patch is to accelerate live migration by skipping the transfer of free pages reported from the guest. A popular method used by the hypervisor to track which part of memory is written during live migration is to write-protect all the guest memory. So, those pages that are reported as free pages but are written after the report function returns will be captured by the hypervisor, and they will be added to the next round of memory transfer.OK, looks much better. I still have few nits.+extern void walk_free_mem_block(void *opaque, + int min_order, + bool (*report_page_block)(void *, unsigned long, + unsigned long)); +please add names to arguments of the prototype/* * Free reserved pages within range [PAGE_ALIGN(start), end & PAGE_MASK) * into the buddy system. The freed pages will be poisoned with pattern diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 6d00f74..81eedc7 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4762,6 +4762,71 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask) show_swap_cache_info(); }+/**+ * walk_free_mem_block - Walk through the free page blocks in the system + * @opaque: the context passed from the caller + * @min_order: the minimum order of free lists to check + * @report_page_block: the callback function to report free page blockspage_block has meaning in the core MM which doesn't strictly match its usage here. Moreover we are reporting pfn ranges rather than struct page range. So report_pfn_range would suit better. [...]+ for_each_populated_zone(zone) { + for (order = MAX_ORDER - 1; order >= min_order; order--) { + for (mt = 0; !stop && mt < MIGRATE_TYPES; mt++) { + spin_lock_irqsave(&zone->lock, flags); + list = &zone->free_area[order].free_list[mt]; + list_for_each_entry(page, list, lru) { + pfn = page_to_pfn(page); + stop = report_page_block(opaque, pfn, + 1 << order); + if (stop) + break;if (stop) { spin_unlock_irqrestore(&zone->lock, flags); return; } would be both easier and less error prone. E.g. You wouldn't pointlessly iterate over remaining orders just to realize there is nothing to be done for those...
Yes, that's better, thanks. I will take other suggestions as well. Best, Wei
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