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authorNick Piggin <nickpiggin@yahoo.com.au>2009-06-16 15:31:39 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-06-16 19:47:30 -0700
commitd2bf6be8ab63aa84e6149aac934649aadf3828b1 (patch)
tree65e7f74f1ed6fd9516f1615b0f293d2aaeede07b /mm/util.c
parent7ffc59b4d0bdfa00e882339f85b8a969bb7021e2 (diff)
downloadlinux-d2bf6be8ab63aa84e6149aac934649aadf3828b1.tar.gz
mm: clean up get_user_pages_fast() documentation
Move more documentation for get_user_pages_fast into the new kerneldoc comment. Add some comments for get_user_pages as well. Also, move get_user_pages_fast declaration up to get_user_pages. It wasn't there initially because it was once a static inline function. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: Andy Grover <andy.grover@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/util.c')
-rw-r--r--mm/util.c16
1 files changed, 12 insertions, 4 deletions
diff --git a/mm/util.c b/mm/util.c
index abc65aa7cdf..d5d2213728c 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -233,13 +233,21 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
* @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.
+ *
+ * get_user_pages_fast provides equivalent functionality to get_user_pages,
+ * operating on current and current->mm, with force=0 and vma=NULL. However
+ * unlike get_user_pages, it must be called without mmap_sem held.
+ *
+ * get_user_pages_fast may take mmap_sem and page table locks, so no
+ * assumptions can be made about lack of locking. get_user_pages_fast is to be
+ * implemented in a way that is advantageous (vs get_user_pages()) when the
+ * user memory area is already faulted in and present in ptes. However if the
+ * pages have to be faulted in, it may turn out to be slightly slower so
+ * callers need to carefully consider what to use. On many architectures,
+ * get_user_pages_fast simply falls back to get_user_pages.
*/
int __attribute__((weak)) get_user_pages_fast(unsigned long start,
int nr_pages, int write, struct page **pages)