Re: [Qemu-devel] [PATCH v9 3/5] mm: function to offer a page block on the free list

[Wei Wang <wei.w.wang@intel.com>]

On 04/14/2017 04:02 AM, Andrew Morton wrote:
> On Thu, 13 Apr 2017 17:35:06 +0800 Wei Wang <wei.w.wang@intel.com> wrote:
>
>> Add a function to find a page block on the free list specified by the
>> caller. Pages from the page block may be used immediately after the
>> function returns. The caller is responsible for detecting or preventing
>> the use of such pages.
>>
>> ...
>>
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -4498,6 +4498,93 @@ void show_free_areas(unsigned int filter)
>>   	show_swap_cache_info();
>>   }
>>   
>> +/**
>> + * Heuristically get a page block in the system that is unused.
>> + * It is possible that pages from the page block are used immediately after
>> + * inquire_unused_page_block() returns. It is the caller's responsibility
>> + * to either detect or prevent the use of such pages.
>> + *
>> + * The free list to check: zone->free_area[order].free_list[migratetype].
>> + *
>> + * If the caller supplied page block (i.e. **page) is on the free list, offer
>> + * the next page block on the list to the caller. Otherwise, offer the first
>> + * page block on the list.
>> + *
>> + * Return 0 when a page block is found on the caller specified free list.
>> + */
>> +int inquire_unused_page_block(struct zone *zone, unsigned int order,
>> +			      unsigned int migratetype, struct page **page)
>> +{
> Perhaps we can wrap this in the appropriate ifdef so the kernels which
> won't be using virtio-balloon don't carry the added overhead.
>
>

OK. What do you think if we add this:

#if defined(CONFIG_VIRTIO_BALLOON) || defined(CONFIG_VIRTIO_BALLOON_MODULE)



Best,
Wei