mm: use vma_iter_clear_gfp() in nommu

Move the definition of vma_iter_clear_gfp() from mmap.c to internal.h so
it can be used in the nommu code.  This will reduce node preallocations
in nommu.

Link: https://lkml.kernel.org/r/20230724183157.3939892-10-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/internal.h

@@ -1064,6 +1064,18 @@ static inline void vma_iter_clear(struct vma_iterator *vmi,
 	mas_store_prealloc(&vmi->mas, NULL);
 }
 
+static inline int vma_iter_clear_gfp(struct vma_iterator *vmi,
+			unsigned long start, unsigned long end, gfp_t gfp)
+{
+	vmi->mas.index = start;
+	vmi->mas.last = end - 1;
+	mas_store_gfp(&vmi->mas, NULL, gfp);
+	if (unlikely(mas_is_err(&vmi->mas)))
+		return -ENOMEM;
+
+	return 0;
+}
+
 static inline struct vm_area_struct *vma_iter_load(struct vma_iterator *vmi)
 {
 	return mas_walk(&vmi->mas);

mm/mmap.c

@@ -154,18 +154,6 @@ static inline struct vm_area_struct *vma_prev_limit(struct vma_iterator *vmi,
 	return mas_prev(&vmi->mas, min);
 }
 
-static inline int vma_iter_clear_gfp(struct vma_iterator *vmi,
-			unsigned long start, unsigned long end, gfp_t gfp)
-{
-	vmi->mas.index = start;
-	vmi->mas.last = end - 1;
-	mas_store_gfp(&vmi->mas, NULL, gfp);
-	if (unlikely(mas_is_err(&vmi->mas)))
-		return -ENOMEM;
-
-	return 0;
-}
-
 /*
  * check_brk_limits() - Use platform specific check of range & verify mlock
  * limits.

mm/nommu.c

@@ -1396,17 +1396,13 @@ static int vmi_shrink_vma(struct vma_iterator *vmi,
 
 	/* adjust the VMA's pointers, which may reposition it in the MM's tree
 	 * and list */
-	if (vma_iter_prealloc(vmi)) {
-		pr_warn("Allocation of vma tree for process %d failed\n",
-		       current->pid);
-		return -ENOMEM;
-	}
-
 	if (from > vma->vm_start) {
-		vma_iter_clear(vmi, from, vma->vm_end);
+		if (vma_iter_clear_gfp(vmi, from, vma->vm_end, GFP_KERNEL))
+			return -ENOMEM;
 		vma->vm_end = from;
 	} else {
-		vma_iter_clear(vmi, vma->vm_start, to);
+		if (vma_iter_clear_gfp(vmi, vma->vm_start, to, GFP_KERNEL))
+			return -ENOMEM;
 		vma->vm_start = to;
 	}