[PATCH v2 10/70] mm/mmap: Change unmapped_area and unmapped_area_topdown to use maple tree

["Liam R. Howlett" <Liam.Howlett@Oracle.com>]

Use the new maple tree data structure to find an unmapped area.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
---
 mm/mmap.c | 249 ++++++------------------------------------------------
 1 file changed, 27 insertions(+), 222 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index f123f9c97dfe8..3b3084ee309b7 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2040,260 +2040,65 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	return error;
 }
 
+/* unmapped_area() Find an area between the low_limit and the high_limit with
+ * the correct alignment and offset, all from @info. Note: current->mm is used
+ * for the search.
+ *
+ * @info: The unmapped area information including the range (low_limit -
+ * hight_limit), the alignment offset and mask.
+ *
+ * Return: A memory address or -ENOMEM.
+ */
 static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
 {
-	/*
-	 * We implement the search by looking for an rbtree node that
-	 * immediately follows a suitable gap. That is,
-	 * - gap_start = vma->vm_prev->vm_end <= info->high_limit - length;
-	 * - gap_end   = vma->vm_start        >= info->low_limit  + length;
-	 * - gap_end - gap_start >= length
-	 */
+	unsigned long length, gap;
 
-	struct mm_struct *mm = current->mm;
-	struct vm_area_struct *vma;
-	unsigned long length, low_limit, high_limit, gap_start, gap_end;
-	unsigned long gap;
+	MA_STATE(mas, &current->mm->mm_mt, 0, 0);
+	validate_mm(current->mm);
 
-	MA_STATE(mas, &mm->mm_mt, 0, 0);
 	/* Adjust search length to account for worst case alignment overhead */
 	length = info->length + info->align_mask;
 	if (length < info->length)
 		return -ENOMEM;
 
-
-	/* Maple tree is self contained. */
-	rcu_read_lock();
 	if (mas_get_empty_area(&mas, info->low_limit, info->high_limit - 1,
 				  length)) {
 		rcu_read_unlock();
 		return -ENOMEM;
 	}
-	rcu_read_unlock();
 	gap = mas.index;
 	gap += (info->align_offset - gap) & info->align_mask;
-
-	/* Adjust search limits by the desired length */
-	if (info->high_limit < length)
-		return -ENOMEM;
-	high_limit = info->high_limit - length;
-
-	if (info->low_limit > high_limit)
-		return -ENOMEM;
-	low_limit = info->low_limit + length;
-
-	/* Check if rbtree root looks promising */
-	if (RB_EMPTY_ROOT(&mm->mm_rb))
-		goto check_highest;
-	vma = rb_entry(mm->mm_rb.rb_node, struct vm_area_struct, vm_rb);
-	if (vma->rb_subtree_gap < length)
-		goto check_highest;
-
-	while (true) {
-		/* Visit left subtree if it looks promising */
-		gap_end = vm_start_gap(vma);
-		if (gap_end >= low_limit && vma->vm_rb.rb_left) {
-			struct vm_area_struct *left =
-				rb_entry(vma->vm_rb.rb_left,
-					 struct vm_area_struct, vm_rb);
-			if (left->rb_subtree_gap >= length) {
-				vma = left;
-				continue;
-			}
-		}
-
-		gap_start = vma->vm_prev ? vm_end_gap(vma->vm_prev) : 0;
-check_current:
-		/* Check if current node has a suitable gap */
-		if (gap_start > high_limit)
-			return -ENOMEM;
-		if (gap_end >= low_limit &&
-		    gap_end > gap_start && gap_end - gap_start >= length)
-			goto found;
-
-		/* Visit right subtree if it looks promising */
-		if (vma->vm_rb.rb_right) {
-			struct vm_area_struct *right =
-				rb_entry(vma->vm_rb.rb_right,
-					 struct vm_area_struct, vm_rb);
-			if (right->rb_subtree_gap >= length) {
-				vma = right;
-				continue;
-			}
-		}
-
-		/* Go back up the rbtree to find next candidate node */
-		while (true) {
-			struct rb_node *prev = &vma->vm_rb;
-			if (!rb_parent(prev))
-				goto check_highest;
-			vma = rb_entry(rb_parent(prev),
-				       struct vm_area_struct, vm_rb);
-			if (prev == vma->vm_rb.rb_left) {
-				gap_start = vm_end_gap(vma->vm_prev);
-				gap_end = vm_start_gap(vma);
-				goto check_current;
-			}
-		}
-	}
-
-check_highest:
-	/* Check highest gap, which does not precede any rbtree node */
-	gap_start = mm->highest_vm_end;
-	gap_end = ULONG_MAX;  /* Only for VM_BUG_ON below */
-	if (gap_start > high_limit)
-		return -ENOMEM;
-
-found:
-	/* We found a suitable gap. Clip it with the original low_limit. */
-	if (gap_start < info->low_limit)
-		gap_start = info->low_limit;
-
-	/* Adjust gap address to the desired alignment */
-	gap_start += (info->align_offset - gap_start) & info->align_mask;
-
-	VM_BUG_ON(gap_start + info->length > info->high_limit);
-	VM_BUG_ON(gap_start + info->length > gap_end);
-
-	VM_BUG_ON(gap != gap_start);
-	return gap_start;
+	return gap;
 }
 
+/* unmapped_area() Find an area between the low_limit and the high_limit with
+ * the correct alignment and offset at the highest available address, all from
+ * @info. Note: current->mm is used for the search.
+ *
+ * @info: The unmapped area information including the range (low_limit -
+ * hight_limit), the alignment offset and mask.
+ *
+ * Return: A memory address or -ENOMEM.
+ */
 static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
 {
-	struct mm_struct *mm = current->mm;
-	struct vm_area_struct *vma = NULL;
-	unsigned long length, low_limit, high_limit, gap_start, gap_end;
-	unsigned long gap;
+	unsigned long length, gap;
 
-	MA_STATE(mas, &mm->mm_mt, 0, 0);
-	validate_mm_mt(mm);
+	MA_STATE(mas, &current->mm->mm_mt, 0, 0);
+	validate_mm_mt(current->mm);
 	/* Adjust search length to account for worst case alignment overhead */
 	length = info->length + info->align_mask;
 	if (length < info->length)
 		return -ENOMEM;
 
-	rcu_read_lock();
-	if (mas_get_empty_area_rev(&mas, info->low_limit, info->high_limit,
+	if (mas_get_empty_area_rev(&mas, info->low_limit, info->high_limit - 1,
 				length)) {
 		rcu_read_unlock();
 		return -ENOMEM;
 	}
-	rcu_read_unlock();
 	gap = (mas.index + info->align_mask) & ~info->align_mask;
 	gap -= info->align_offset & info->align_mask;
-	/*
-	 * Adjust search limits by the desired length.
-	 * See implementation comment at top of unmapped_area().
-	 */
-	gap_end = info->high_limit;
-	if (gap_end < length)
-		return -ENOMEM;
-	high_limit = gap_end - length;
-
-	if (info->low_limit > high_limit)
-		return -ENOMEM;
-	low_limit = info->low_limit + length;
-
-	/* Check highest gap, which does not precede any rbtree node */
-	gap_start = mm->highest_vm_end;
-	if (gap_start <= high_limit)
-		goto found_highest;
-
-	/* Check if rbtree root looks promising */
-	if (RB_EMPTY_ROOT(&mm->mm_rb))
-		return -ENOMEM;
-	vma = rb_entry(mm->mm_rb.rb_node, struct vm_area_struct, vm_rb);
-	if (vma->rb_subtree_gap < length)
-		return -ENOMEM;
-
-	while (true) {
-		/* Visit right subtree if it looks promising */
-		gap_start = vma->vm_prev ? vm_end_gap(vma->vm_prev) : 0;
-		if (gap_start <= high_limit && vma->vm_rb.rb_right) {
-			struct vm_area_struct *right =
-				rb_entry(vma->vm_rb.rb_right,
-					 struct vm_area_struct, vm_rb);
-			if (right->rb_subtree_gap >= length) {
-				vma = right;
-				continue;
-			}
-		}
-
-check_current:
-		/* Check if current node has a suitable gap */
-		gap_end = vm_start_gap(vma);
-		if (gap_end < low_limit)
-			return -ENOMEM;
-		if (gap_start <= high_limit &&
-		    gap_end > gap_start && gap_end - gap_start >= length)
-			goto found;
-
-		/* Visit left subtree if it looks promising */
-		if (vma->vm_rb.rb_left) {
-			struct vm_area_struct *left =
-				rb_entry(vma->vm_rb.rb_left,
-					 struct vm_area_struct, vm_rb);
-			if (left->rb_subtree_gap >= length) {
-				vma = left;
-				continue;
-			}
-		}
-
-		/* Go back up the rbtree to find next candidate node */
-		while (true) {
-			struct rb_node *prev = &vma->vm_rb;
-			if (!rb_parent(prev))
-				return -ENOMEM;
-			vma = rb_entry(rb_parent(prev),
-				       struct vm_area_struct, vm_rb);
-			if (prev == vma->vm_rb.rb_right) {
-				gap_start = vma->vm_prev ?
-					vm_end_gap(vma->vm_prev) : 0;
-				goto check_current;
-			}
-		}
-	}
-
-found:
-	/* We found a suitable gap. Clip it with the original high_limit. */
-	if (gap_end > info->high_limit)
-		gap_end = info->high_limit;
-
-found_highest:
-	/* Compute highest gap address at the desired alignment */
-	gap_end -= info->length;
-	gap_end -= (gap_end - info->align_offset) & info->align_mask;
-
-	VM_BUG_ON(gap_end < info->low_limit);
-	VM_BUG_ON(gap_end < gap_start);
-
-	if (gap != gap_end) {
-		pr_err("%s: %px Gap was found: mt %lu gap_end %lu\n", __func__,
-				mm, gap, gap_end);
-		pr_err("window was %lu - %lu size %lu\n", info->high_limit,
-				info->low_limit, length);
-		pr_err("mas.min %lu max %lu mas.last %lu\n", mas.min, mas.max,
-				mas.last);
-		pr_err("mas.index %lu align mask %lu offset %lu\n", mas.index,
-				info->align_mask, info->align_offset);
-		pr_err("rb_find_vma find on %lu => %px (%px)\n", mas.index,
-				find_vma(mm, mas.index), vma);
-#if defined(CONFIG_DEBUG_MAPLE_TREE)
-		mt_dump(&mm->mm_mt);
-#endif
-		{
-			struct vm_area_struct *dv = mm->mmap;
-
-			while (dv) {
-				printk("vma %px %lu-%lu\n", dv, dv->vm_start, dv->vm_end);
-				dv = dv->vm_next;
-			}
-		}
-		VM_BUG_ON(gap != gap_end);
-	}
-
-	return gap_end;
+	return gap;
 }
 
 /*
-- 
2.28.0