mm: add alloc_pages_exact() and free_pages_exact()

extern unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order);

extern unsigned long get_zeroed_page(gfp_t gfp_mask);

void *alloc_pages_exact(size_t size, gfp_t gfp_mask);

void free_pages_exact(void *virt, size_t size);

#define __get_free_page(gfp_mask) \

		__get_free_pages((gfp_mask),0)

EXPORT_SYMBOL(free_pages);

/**

 * alloc_pages_exact - allocate an exact number physically-contiguous pages.

 * @size: the number of bytes to allocate

 * @gfp_mask: GFP flags for the allocation

 *

 * This function is similar to alloc_pages(), except that it allocates the

 * minimum number of pages to satisfy the request.  alloc_pages() can only

 * allocate memory in power-of-two pages.

 *

 * This function is also limited by MAX_ORDER.

 *

 * Memory allocated by this function must be released by free_pages_exact().

 */

void *alloc_pages_exact(size_t size, gfp_t gfp_mask)

{

	unsigned int order = get_order(size);

	unsigned long addr;

	addr = __get_free_pages(gfp_mask, order);

	if (addr) {

		unsigned long alloc_end = addr + (PAGE_SIZE << order);

		unsigned long used = addr + PAGE_ALIGN(size);

		split_page(virt_to_page(addr), order);

		while (used < alloc_end) {

			free_page(used);

			used += PAGE_SIZE;

		}

	}

	return (void *)addr;

}

EXPORT_SYMBOL(alloc_pages_exact);

/**

 * free_pages_exact - release memory allocated via alloc_pages_exact()

 * @virt: the value returned by alloc_pages_exact.

 * @size: size of allocation, same value as passed to alloc_pages_exact().

 *

 * Release the memory allocated by a previous call to alloc_pages_exact.

 */

void free_pages_exact(void *virt, size_t size)

{

	unsigned long addr = (unsigned long)virt;

	unsigned long end = addr + PAGE_ALIGN(size);

	while (addr < end) {

		free_page(addr);

		addr += PAGE_SIZE;

	}

}

EXPORT_SYMBOL(free_pages_exact);

static unsigned int nr_free_zone_pages(int offset)

{

	struct zoneref *z;