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From:   Liam Howlett <liam.howlett@oracle.com>
To:     "maple-tree@lists.infradead.org" <maple-tree@lists.infradead.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Yu Zhao <yuzhao@google.com>
Subject: [PATCH v8 19/70] mmap: change zeroing of maple tree in __vma_adjust()
Thread-Topic: [PATCH v8 19/70] mmap: change zeroing of maple tree in
 __vma_adjust()
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Date:   Tue, 26 Apr 2022 15:06:34 +0000
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From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>

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.

The change requires a custom search for the linked list addition to find
the correct VMA for the prev link.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---
 mm/mmap.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 622ccc28940f..ec09b68a3e0a 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -597,11 +597,11 @@ static int vma_link(struct mm_struct *mm, struct vm_a=
rea_struct *vma,
  * mm's list and the mm tree.  It has already been inserted into the inter=
val tree.
  */
 static void __insert_vm_struct(struct mm_struct *mm, struct ma_state *mas,
-			       struct vm_area_struct *vma)
+		struct vm_area_struct *vma, unsigned long location)
 {
 	struct vm_area_struct *prev;
=20
-	mas_set(mas, vma->vm_start);
+	mas_set(mas, location);
 	prev =3D mas_prev(mas, 0);
 	mas_reset(mas);
 	vma_mas_store(vma, mas);
@@ -632,6 +632,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned l=
ong start,
 	int remove_next =3D 0;
 	MA_STATE(mas, &mm->mm_mt, 0, 0);
 	struct vm_area_struct *exporter =3D NULL, *importer =3D NULL;
+	unsigned long ll_prev =3D vma->vm_start; /* linked list prev. */
=20
 	if (next && !insert) {
 		if (end >=3D next->vm_end) {
@@ -763,17 +764,27 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned=
 long start,
 	}
=20
 	if (start !=3D vma->vm_start) {
-		if (vma->vm_start < start)
+		if ((vma->vm_start < start) &&
+		    (!insert || (insert->vm_end !=3D start))) {
 			vma_mt_szero(mm, vma->vm_start, start);
-		else
+			VM_WARN_ON(insert && insert->vm_start > vma->vm_start);
+		} else {
 			vma_changed =3D true;
+		}
 		vma->vm_start =3D start;
 	}
 	if (end !=3D 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->vm_start !=3D end)) {
+				vma_mt_szero(mm, end, vma->vm_end);
+				VM_WARN_ON(insert &&
+					   insert->vm_end < vma->vm_end);
+			} else if (insert->vm_start =3D=3D end) {
+				ll_prev =3D vma->vm_end;
+			}
+		} else {
 			vma_changed =3D true;
+		}
 		vma->vm_end =3D end;
 		if (!next)
 			mm->highest_vm_end =3D vm_end_gap(vma);
@@ -808,7 +819,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned l=
ong start,
 		 * us to insert it before dropping the locks
 		 * (it may either follow vma or precede it).
 		 */
-		__insert_vm_struct(mm, &mas, insert);
+		__insert_vm_struct(mm, &mas, insert, ll_prev);
 	}
=20
 	if (anon_vma) {
--=20
2.35.1