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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>,
        Hugh Dickins <hughd@google.com>
CC:     Yu Zhao <yuzhao@google.com>
Subject: [PATCH v12 18/69] mmap: change zeroing of maple tree in
 __vma_adjust()
Thread-Topic: [PATCH v12 18/69] mmap: change zeroing of maple tree in
 __vma_adjust()
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Date:   Wed, 20 Jul 2022 02:17:49 +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.

Link: https://lkml.kernel.org/r/20220504011345.662299-3-Liam.Howlett@oracle=
.com
Link: https://lkml.kernel.org/r/20220621204632.3370049-19-Liam.Howlett@orac=
le.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 mm/mmap.c | 30 ++++++++++++++++++++++--------
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 71713c661db0..02d2fd90af80 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -614,11 +614,11 @@ 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);
 	vma_mas_store(vma, mas);
 	__vma_link_list(mm, vma, prev);
@@ -648,6 +648,7 @@ 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) {
@@ -775,15 +776,27 @@ 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_mas_szero(&mas, vma->vm_start, start);
-		vma_changed =3D true;
+			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_mas_szero(&mas, end, vma->vm_end);
-		vma_changed =3D true;
+		if (vma->vm_end > end) {
+			if (!insert || (insert->vm_start !=3D end)) {
+				vma_mas_szero(&mas, 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);
@@ -830,7 +843,7 @@ 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) {
@@ -917,6 +930,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned l=
ong start,
 	if (insert && file)
 		uprobe_mmap(insert);
=20
+	mas_destroy(&mas);
 	validate_mm(mm);
 	return 0;
 }
--=20
2.35.1