linux-kernel - [PATCH v2] mm: Correct comments regarding do_fault

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Message-Id: <302D0B14-C7E9-44C6-8BED-033F9ACBD030@oracle.com>
Date:   Fri, 26 Jan 2018 20:25:25 -0700
From:   William Kucharski <william.kucharski@...cle.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH v2] mm: Correct comments regarding do_fault_around() 

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
aecd6f44266c13b8709245b21ded2d19291ab070.

Signed-off-by: William Kucharski <william.kucharski@...cle.com>
Reviewed-by: Larry Bassel <larry.bassel@...cle.com>
---
 memory.c |   22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 793004608332..885dffe194f8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3485,9 +3485,8 @@ 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)
 {
@@ -3530,13 +3529,14 @@ 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)
 {
@@ -3553,8 +3553,8 @@ 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)) +