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 eb32bbd8f43977de1ce2fe1d7176edbcd53662c4..f1b95a1d9705f2332bdca21913d0926f866f41dd 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -635,6 +635,7 @@ 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;
@@ -760,25 +761,29 @@ 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) {