Messages in this thread | | | Date | Tue, 29 Aug 2017 11:23:52 +0800 | From | Wei Wang <> | Subject | Re: [PATCH v15 4/5] mm: support reporting free page blocks |
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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 blocks > page_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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