slab: document kzfree() zeroing behavior

[sfrench/cifs-2.6.git] / mm / util.c

diff --git a/mm/util.c b/mm/util.c
index 2599e83eea17a9c9673c26507541b12581e952f0..e79572b3684ccb9f467d42b4f18420640e706b07 100644 (file)
--- a/mm/util.c
+++ b/mm/util.c
@@ -166,6 +166,10 @@ EXPORT_SYMBOL(krealloc);
  *
  * The memory of the object @p points to is zeroed before freed.
  * If @p is %NULL, kzfree() does nothing.
+ *
+ * Note: this function zeroes the whole allocated buffer which can be a good
+ * deal bigger than the requested buffer size passed to kmalloc(). So be
+ * careful when using this function in performance sensitive code.
  */
 void kzfree(const void *p)
 {
@@ -223,6 +227,22 @@ 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)
 {