mm: vma_adjust: remove superfluous confusing update in remove_next == 1 case

mm->highest_vm_end doesn't need any update.

After finally removing the oddness from vma_merge case 8 that was
causing:

1) constant risk of trouble whenever anybody would check vma fields
   from rmap_walks, like it happened when page migration was
   introduced and it read the vma->vm_page_prot from a rmap_walk

2) the callers of vma_merge to re-initialize any value different from
   the current vma, instead of vma_merge() more reliably returning a
   vma that already matches all fields passed as parameter

.. it is also worth to take the opportunity of cleaning up superfluous
code in vma_adjust(), that if not removed adds up to the hard
readability of the function.

Link: http://lkml.kernel.org/r/1474492522-2261-5-git-send-email-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Jan Vorlicek <janvorli@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index b3b74cc705aea3e43741838e712a6244af8b7a45..183694b80bcc85f1ae7ec050135648046133c4c2 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -817,8 +817,28 @@ again:
                }
                else if (next)
                        vma_gap_update(next);
-               else
-                       mm->highest_vm_end = end;
+               else {
+                       /*
+                        * If remove_next == 2 we obviously can't
+                        * reach this path.
+                        *
+                        * If remove_next == 3 we can't reach this
+                        * path because pre-swap() next is always not
+                        * NULL. pre-swap() "next" is not being
+                        * removed and its next->vm_end is not altered
+                        * (and furthermore "end" already matches
+                        * next->vm_end in remove_next == 3).
+                        *
+                        * We reach this only in the remove_next == 1
+                        * case if the "next" vma that was removed was
+                        * the highest vma of the mm. However in such
+                        * case next->vm_end == "end" and the extended
+                        * "vma" has vma->vm_end == next->vm_end so
+                        * mm->highest_vm_end doesn't need any update
+                        * in remove_next == 1 case.
+                        */
+                       VM_WARN_ON(mm->highest_vm_end != end);
+               }
        }
        if (insert && file)
                uprobe_mmap(insert);