mm: correct comments regarding do_fault_around()

There are multiple comments surrounding do_fault_around that memtion
fault_around_pages() and fault_around_mask(), two routines that do not
exist.  These comments should be reworded to reference
fault_around_bytes, the value which is used to determine how much
do_fault_around() will attempt to read when processing a fault.

These comments should have been updated when fault_around_pages() and
fault_around_mask() were removed in commit aecd6f44266c ("mm: close race
between do_fault_around() and fault_around_bytes_set()").

Fixes: aecd6f44266c1 ("mm: close race between do_fault_around() and fault_around_bytes_set()")
Link: http://lkml.kernel.org/r/302D0B14-C7E9-44C6-8BED-033F9ACBD030@oracle.com
Signed-off-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Larry Bassel <larry.bassel@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory.c

@@ -3511,9 +3511,8 @@ static int fault_around_bytes_get(void *data, u64 *val)
 }
 
 /*
- * fault_around_pages() and fault_around_mask() expects fault_around_bytes
- * rounded down to nearest page order. It's what do_fault_around() expects to
- * see.
+ * fault_around_bytes must be rounded down to the nearest page order as it's
+ * what do_fault_around() expects to see.
  */
 static int fault_around_bytes_set(void *data, u64 val)
 {
@@ -3556,13 +3555,14 @@ late_initcall(fault_around_debugfs);
  * This function doesn't cross the VMA boundaries, in order to call map_pages()
  * only once.
  *
- * fault_around_pages() defines how many pages we'll try to map.
- * do_fault_around() expects it to return a power of two less than or equal to
- * PTRS_PER_PTE.
+ * fault_around_bytes defines how many bytes we'll try to map.
+ * do_fault_around() expects it to be set to a power of two less than or equal
+ * to PTRS_PER_PTE.
  *
- * The virtual address of the area that we map is naturally aligned to the
- * fault_around_pages() value (and therefore to page order).  This way it's
- * easier to guarantee that we don't cross page table boundaries.
+ * The virtual address of the area that we map is naturally aligned to
+ * fault_around_bytes rounded down to the machine page size
+ * (and therefore to page order).  This way it's easier to guarantee
+ * that we don't cross page table boundaries.
  */
 static int do_fault_around(struct vm_fault *vmf)
 {
@@ -3579,8 +3579,8 @@ static int do_fault_around(struct vm_fault *vmf)
 	start_pgoff -= off;
 
 	/*
-	 *  end_pgoff is either end of page table or end of vma
-	 *  or fault_around_pages() from start_pgoff, depending what is nearest.
+	 *  end_pgoff is either the end of the page table, the end of
+	 *  the vma or nr_pages from start_pgoff, depending what is nearest.
 	 */
 	end_pgoff = start_pgoff -
 		((vmf->address >> PAGE_SHIFT) & (PTRS_PER_PTE - 1)) +