[PATCH v5 57/70] mm/mempolicy: Use vma iterator & maple state instead of vma linked list

[Liam Howlett <liam.howlett@oracle.com>]

From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>

Reworked the way mbind_range() finds the first VMA to reuse the maple
state and limit the number of tree walks needed.

Note, this drops the VM_BUG_ON(!vma) call, which would catch a start
address higher than the last VMA.  The code was written in a way that
allowed no VMA updates to occur and still return success.  There should
be no functional change to this scenario with the new code.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
---
 mm/mempolicy.c | 58 +++++++++++++++++++++++++++-----------------------
 1 file changed, 31 insertions(+), 27 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 028e8dd82b44..d058b2be8655 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -380,9 +380,10 @@ void mpol_rebind_task(struct task_struct *tsk, const nodemask_t *new)
 void mpol_rebind_mm(struct mm_struct *mm, nodemask_t *new)
 {
 	struct vm_area_struct *vma;
+	VMA_ITERATOR(vmi, mm, 0);
 
 	mmap_write_lock(mm);
-	for (vma = mm->mmap; vma; vma = vma->vm_next)
+	for_each_vma(vmi, vma)
 		mpol_rebind_policy(vma->vm_policy, new);
 	mmap_write_unlock(mm);
 }
@@ -655,7 +656,7 @@ static unsigned long change_prot_numa(struct vm_area_struct *vma,
 static int queue_pages_test_walk(unsigned long start, unsigned long end,
 				struct mm_walk *walk)
 {
-	struct vm_area_struct *vma = walk->vma;
+	struct vm_area_struct *next, *vma = walk->vma;
 	struct queue_pages *qp = walk->private;
 	unsigned long endvma = vma->vm_end;
 	unsigned long flags = qp->flags;
@@ -670,9 +671,10 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
 			/* hole at head side of range */
 			return -EFAULT;
 	}
+	next = find_vma(vma->vm_mm, vma->vm_end);
 	if (!(flags & MPOL_MF_DISCONTIG_OK) &&
 		((vma->vm_end < qp->end) &&
-		(!vma->vm_next || vma->vm_end < vma->vm_next->vm_start)))
+		(!next || vma->vm_end < next->vm_start)))
 		/* hole at middle or tail of range */
 		return -EFAULT;
 
@@ -786,28 +788,24 @@ static int vma_replace_policy(struct vm_area_struct *vma,
 static int mbind_range(struct mm_struct *mm, unsigned long start,
 		       unsigned long end, struct mempolicy *new_pol)
 {
-	struct vm_area_struct *next;
+	MA_STATE(mas, &mm->mm_mt, start - 1, start - 1);
 	struct vm_area_struct *prev;
 	struct vm_area_struct *vma;
 	int err = 0;
 	pgoff_t pgoff;
-	unsigned long vmstart;
-	unsigned long vmend;
-
-	vma = find_vma(mm, start);
-	VM_BUG_ON(!vma);
 
-	prev = vma->vm_prev;
-	if (start > vma->vm_start)
-		prev = vma;
+	prev = mas_find_rev(&mas, 0);
+	if (prev && (start < prev->vm_end))
+		vma = prev;
+	else
+		vma = mas_next(&mas, end - 1);
 
-	for (; vma && vma->vm_start < end; prev = vma, vma = next) {
-		next = vma->vm_next;
-		vmstart = max(start, vma->vm_start);
-		vmend   = min(end, vma->vm_end);
+	for (; vma; vma = mas_next(&mas, end - 1)) {
+		unsigned long vmstart = max(start, vma->vm_start);
+		unsigned long vmend = min(end, vma->vm_end);
 
 		if (mpol_equal(vma_policy(vma), new_pol))
-			continue;
+			goto next;
 
 		pgoff = vma->vm_pgoff +
 			((vmstart - vma->vm_start) >> PAGE_SHIFT);
@@ -816,8 +814,9 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
 				 new_pol, vma->vm_userfaultfd_ctx,
 				 vma_anon_name(vma));
 		if (prev) {
+			/* vma_merge() invalidated the mas */
+			mas_pause(&mas);
 			vma = prev;
-			next = vma->vm_next;
 			if (mpol_equal(vma_policy(vma), new_pol))
 				continue;
 			/* vma_merge() joined vma && vma->next, case 8 */
@@ -827,19 +826,24 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
 			err = split_vma(vma->vm_mm, vma, vmstart, 1);
 			if (err)
 				goto out;
+			/* split_vma() invalidated the mas */
+			mas_pause(&mas);
 		}
 		if (vma->vm_end != vmend) {
 			err = split_vma(vma->vm_mm, vma, vmend, 0);
 			if (err)
 				goto out;
+			/* mas_pause() unnecessary as the loop is ending */
 		}
- replace:
+replace:
 		err = vma_replace_policy(vma, new_pol);
 		if (err)
 			goto out;
+next:
+		prev = vma;
 	}
 
- out:
+out:
 	return err;
 }
 
@@ -1057,6 +1061,7 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
 			   int flags)
 {
 	nodemask_t nmask;
+	struct vm_area_struct *vma;
 	LIST_HEAD(pagelist);
 	int err = 0;
 	struct migration_target_control mtc = {
@@ -1072,8 +1077,9 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
 	 * need migration.  Between passing in the full user address
 	 * space range and MPOL_MF_DISCONTIG_OK, this call can not fail.
 	 */
+	vma = find_vma(mm, 0);
 	VM_BUG_ON(!(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)));
-	queue_pages_range(mm, mm->mmap->vm_start, mm->task_size, &nmask,
+	queue_pages_range(mm, vma->vm_start, mm->task_size, &nmask,
 			flags | MPOL_MF_DISCONTIG_OK, &pagelist);
 
 	if (!list_empty(&pagelist)) {
@@ -1202,13 +1208,12 @@ static struct page *new_page(struct page *page, unsigned long start)
 {
 	struct vm_area_struct *vma;
 	unsigned long address;
+	VMA_ITERATOR(vmi, current->mm, start);
 
-	vma = find_vma(current->mm, start);
-	while (vma) {
+	for_each_vma(vmi, vma) {
 		address = page_address_in_vma(page, vma);
 		if (address != -EFAULT)
 			break;
-		vma = vma->vm_next;
 	}
 
 	if (PageHuge(page)) {
@@ -1491,6 +1496,7 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
 	unsigned long vmend;
 	unsigned long end;
 	int err = -ENOENT;
+	VMA_ITERATOR(vmi, mm, start);
 
 	start = untagged_addr(start);
 	if (start & ~PAGE_MASK)
@@ -1516,9 +1522,7 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
 	if (end == start)
 		return 0;
 	mmap_write_lock(mm);
-	vma = find_vma(mm, start);
-	for (; vma && vma->vm_start < end;  vma = vma->vm_next) {
-
+	for_each_vma_range(vmi, vma, end) {
 		vmstart = max(start, vma->vm_start);
 		vmend   = min(end, vma->vm_end);
 		new = mpol_dup(vma_policy(vma));
-- 
2.34.1