diff mbox series

[v4,11/66] mm/mmap: Use maple tree for unmapped_area{_topdown}

Message ID 20211201142918.921493-12-Liam.Howlett@oracle.com (mailing list archive)
State New
Headers show
Series Introducing the Maple Tree | expand

Commit Message

Liam R. Howlett Dec. 1, 2021, 2:29 p.m. UTC 
From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>

The maple tree code was added to find the unmapped area in a previous
commit and was checked against what the rbtree returned, but the actual
result was never used.  Start using the maple tree implementation and
remove the rbtree code.

Add kernel documentation comment for these functions.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
---
 mm/mmap.c | 262 +++++++-----------------------------------------------
 1 file changed, 31 insertions(+), 231 deletions(-)

Comments

Vlastimil Babka Dec. 15, 2021, 4:43 p.m. UTC | #1 
On 12/1/21 15:29, Liam Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
> 
> The maple tree code was added to find the unmapped area in a previous
> commit and was checked against what the rbtree returned, but the actual
> result was never used.  Start using the maple tree implementation and
> remove the rbtree code.

Nice cleanup. But...

> Add kernel documentation comment for these functions.
> 
> Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>

>  
>  	/* 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();
> -	mas_empty_area_rev(&mas, info->low_limit, info->high_limit - 1,
> -			   length);
> -	rcu_read_unlock();

Why is RCU locking being removed as part of this? Ditton in
unmapped_area_topdown()
Liam R. Howlett Dec. 15, 2021, 6:28 p.m. UTC | #2 
* Vlastimil Babka <vbabka@suse.cz> [211215 11:43]:
> On 12/1/21 15:29, Liam Howlett wrote:
> > From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
> > 
> > The maple tree code was added to find the unmapped area in a previous
> > commit and was checked against what the rbtree returned, but the actual
> > result was never used.  Start using the maple tree implementation and
> > remove the rbtree code.
> 
> Nice cleanup. But...
> 
> > Add kernel documentation comment for these functions.
> > 
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
> 
> >  
> >  	/* 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();
> > -	mas_empty_area_rev(&mas, info->low_limit, info->high_limit - 1,
> > -			   length);
> > -	rcu_read_unlock();
> 
> Why is RCU locking being removed as part of this? Ditton in
> unmapped_area_topdown()

It is not needed with the mmap_lock() being used in the maple tree.  But
I should either be consistent and keep it everywhere or not have it in
the earlier patch.  I will fix this, maybe I should have left them in
everywhere.
diff mbox series

Patch

diff --git a/mm/mmap.c b/mm/mmap.c
index 8425ab573770..0ee4e430e4b1 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1995,260 +1995,60 @@  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, &mm->mm_mt, 0, 0);
+	MA_STATE(mas, &current->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;
 
-	rcu_read_lock();
-	mas_empty_area_rev(&mas, info->low_limit, info->high_limit - 1,
-			   length);
-	rcu_read_unlock();
+	if (mas_empty_area(&mas, info->low_limit, info->high_limit - 1,
+				  length))
+		return -ENOMEM;
 	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;
-}
-
-static inline unsigned long top_area_aligned(struct vm_unmapped_area_info *info,
-					     unsigned long end)
-{
-	return (end - info->length - info->align_offset) & (~info->align_mask);
+	return gap;
 }
 
+/* unmapped_area_topdown() 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;
-
-	MA_STATE(mas, &mm->mm_mt, 0, 0);
-	validate_mm_mt(mm);
+	unsigned long length, gap;
 
+	MA_STATE(mas, &current->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;
 
-	rcu_read_lock();
-	mas_empty_area_rev(&mas, info->low_limit, info->high_limit - 1,
-		   length);
-	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)
+	if (mas_empty_area_rev(&mas, info->low_limit, info->high_limit - 1,
+				length))
 		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;
+	gap = (mas.index + info->align_mask) & ~info->align_mask;
+	gap -= info->align_offset & info->align_mask;
+	return gap;
 }
 
 /*