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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: Andy Grover <andy.grover@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andy Grover 2009-04-13 14:40:05 -07:00 committed by Linus Torvalds
parent d20d5a7456
commit 9de100d001
1 changed files with 16 additions and 0 deletions
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16
mm/util.c
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@ -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)
{