[PATCH v4 17/66] mmap: Change zeroing of maple tree in __vma_adjust

[Liam Howlett]

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@xxxxxxxxxx>
---
 mm/mmap.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 93ed19b2c6ce..c5f92666d145 100644
--- 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 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
 			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) {
-- 
2.30.2