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 80daaf67359a93621663c77319206f473ee1999f..d64f09eabe21f5ffa7cd6b8b064523f0f69ae0cd 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -615,6 +615,7 @@ 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;
@@ -740,25 +741,29 @@ 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_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) {