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Commit a0d22f48 authored by Andy Grover's avatar Andy Grover Committed by Ingo Molnar
Browse files

x86: Document get_user_pages_fast() 



While better than get_user_pages(), the usage of gupf(),
especially the return values and the fact that it can
potentially only partially pin the range, warranted some
documentation.

Signed-off-by: default avatarAndy Grover <andy.grover@oracle.com>
Cc: npiggin@suse.de
Cc: akpm@linux-foundation.org
LKML-Reference: <1239320729-3262-1-git-send-email-andy.grover@oracle.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 746cddd3

arch/x86/mm/gup.c

+16 −0
Original line number Diff line number Diff line
@@ -219,6 +219,22 @@ static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end, 
	return 1;

}



/**

 * get_user_pages_fast() - pin user pages in memory

 * @start:	starting user address

 * @nr_pages:	number of pages from start to pin

 * @write:	whether pages will be written to

 * @pages:	array that receives pointers to the pages pinned.

 * 		Should be at least nr_pages long.

 *

 * Attempt to pin user pages in memory without taking mm->mmap_sem.

 * If not successful, it will fall back to taking the lock and

 * calling get_user_pages().

 *

 * Returns number of pages pinned. This may be fewer than the number

 * requested. If nr_pages is 0 or negative, returns 0. If no pages

 * were pinned, returns -errno.

 */

int get_user_pages_fast(unsigned long start, int nr_pages, int write,

			struct page **pages)

{