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Commit 9de100d0 authored by Andy Grover's avatar Andy Grover Committed by Linus Torvalds
Browse files

mm: 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: Ingo Molnar <mingo@elte.hu>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d20d5a74

mm/util.c

+16 −0
Original line number Diff line number Diff line
@@ -223,6 +223,22 @@ void arch_pick_mmap_layout(struct mm_struct *mm) 
}

#endif



/**

 * 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 __attribute__((weak)) get_user_pages_fast(unsigned long start,

				int nr_pages, int write, struct page **pages)

{