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Commit 2be0ffe2 authored by Timur Tabi's avatar Timur Tabi Committed by Linus Torvalds
Browse files

mm: add alloc_pages_exact() and free_pages_exact() 



alloc_pages_exact() is similar to alloc_pages(), except that it allocates
the minimum number of pages to fulfill the request.  This is useful if you
want to allocate a very large buffer that is slightly larger than an even
power-of-two number of pages.  In that case, alloc_pages() will waste a
lot of memory.

I have a video driver that wants to allocate a 5MB buffer.  alloc_pages()
wiill waste 3MB of physically-contiguous memory.

Signed-off-by: default avatarTimur Tabi <timur@freescale.com>
Cc: Andi Kleen <andi@firstfloor.org>
Acked-by: default avatarMel Gorman <mel@csn.ul.ie>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3560e249

include/linux/gfp.h

+3 −0
Original line number Diff line number Diff line
@@ -228,6 +228,9 @@ extern struct page *alloc_page_vma(gfp_t gfp_mask, 
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)

mm/page_alloc.c

+53 −0
Original line number Diff line number Diff line
@@ -1697,6 +1697,59 @@ void free_pages(unsigned long addr, unsigned int order) 


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;