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

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
...@@ -223,6 +223,22 @@ void arch_pick_mmap_layout(struct mm_struct *mm) ...@@ -223,6 +223,22 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
} }
#endif #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 __attribute__((weak)) get_user_pages_fast(unsigned long start,
int nr_pages, int write, struct page **pages) int nr_pages, int write, struct page **pages)
{ {
......
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