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 cee254c7e319907347707da564a28bae4dbfd30c..ff909eb0b9fb289314c1d603dedbb72d82e0c2af 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -638,6 +638,7 @@ 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;
@@ -763,25 +764,29 @@ 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 (!next)
                        mm->highest_vm_end = vm_end_gap(vma);
        }
 
-       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) {