Linux Virtualization - Apr 2017 - [PATCH v9 3/5] mm: function to offer a page block on the free list

On Thu, 13 Apr 2017 17:35:06 +0800 Wei Wang <wei.w.wang at 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.

On 04/14/2017 04:02 AM, Andrew Morton wrote:
> On Thu, 13 Apr 2017 17:35:06 +0800 Wei Wang <wei.w.wang at 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

On Fri, Apr 14, 2017 at 10:30:27AM +0800, Wei Wang
wrote:
> OK. What do you think if we add this:
> 
> #if defined(CONFIG_VIRTIO_BALLOON) || defined(CONFIG_VIRTIO_BALLOON_MODULE)
That's spelled "IS_ENABLED(CONFIG_VIRTIO_BALLOON)", FYI.