[PATCH 4/4] mm: vma_adjust: remove superfluous confusing update in remove_next == 1 case

[Andrea Arcangeli <aarcange@redhat.com>]

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.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---
 mm/mmap.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 57b1eaf..bf2dc6b 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -915,8 +915,28 @@ 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);

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