mmap: Change zeroing of maple tree in __vma_adjust

Only write to the maple tree if we are not inserting or the insert isn't
going to overwrite the area to clear.  This avoids spanning writes and
node coealescing when unnecessary.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>

diff --git a/mm/mmap.c b/mm/mmap.c
index ff158583ee09ce1e2e4bcb78a5235723dc12e0dc..a732f116f0ecfa531b62740897776c596b707963 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -579,7 +579,6 @@ static void vma_link(struct mm_struct *mm, struct vm_area_struct *vma)
  */
 static void __insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
 {
-       BUG_ON(find_vma_intersection(mm, vma->vm_start, vma->vm_end));
        vma_mt_store(mm, vma);
        mm->map_count++;
 }
@@ -698,6 +697,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
        bool vma_changed = false;
        long adjust_next = 0;
        int remove_next = 0;
+       unsigned long old_start;
 
        if (next && !insert) {
                struct vm_area_struct *exporter = NULL, *importer = NULL;
@@ -823,23 +823,27 @@ again:
                        vma_interval_tree_remove(next, root);
        }
 
+       old_start = vma->vm_start;
        if (start != vma->vm_start) {
-               if (vma->vm_start < start)
-                       vma_mt_szero(mm, vma->vm_start, start);
-               else
-                       vma_changed = true;
+               vma_changed = true;
                vma->vm_start = start;
        }
        if (end != vma->vm_end) {
-               if (vma->vm_end > end)
-                       vma_mt_szero(mm, end, vma->vm_end);
-               else
+               if (vma->vm_end > end) {
+                       if (!insert || (insert && (insert->vm_start != end)))
+                               vma_mt_szero(mm, end, vma->vm_end);
+               } else
                        vma_changed = true;
                vma->vm_end = end;
        }
 
-       if (vma_changed)
+       if (vma_changed) {
                vma_mt_store(mm, vma);
+               if (old_start < start) {
+                       if (insert && (insert->vm_start != old_start))
+                               vma_mt_szero(mm, old_start, start);
+               }
+       }
 
        vma->vm_pgoff = pgoff;
        if (adjust_next) {