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SubjectRe: [PATCH -mm v2 01/11] mm: track free size between VMAs in VMA rbtree
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On Thu, 2012-06-21 at 17:57 -0400, Rik van Riel wrote:
> +static unsigned long largest_free_gap(struct rb_node *node)
> +{
> + struct vm_area_struct *vma, *prev, *left = NULL, *right = NULL;
> + unsigned long largest = 0;
> +
> + if (node->rb_left)
> + left = rb_to_vma(node->rb_left);
> + if (node->rb_right)
> + right = rb_to_vma(node->rb_right);
> +
> + /* Calculate the free gap size between us and the VMA to our left. */
> + vma = rb_to_vma(node);
> + prev = vma->vm_prev;
> +
> + if (prev)
> + largest = vma->vm_start - prev->vm_end;
> + else
> + largest = vma->vm_start;
> +
> + /* We propagate the largest of our own, or our children's free gaps. */
> + if (left)
> + largest = max(largest, left->free_gap);
> + if (right)
> + largest = max(largest, right->free_gap);
> +
> + return largest;
> +}

If you introduce helpers like:

static inline struct vm_area_struct *vma_of(struct rb_node *node)
{
return container_of(node, struct vm_area_struct, vm_rb);
}

static inline unsigned long max_gap_of(struct rb_node *node)
{
return vma_of(node)->free_gap;
}

static unsigned long gap_of(struct rb_node *node)
{
struct vm_area_struct *vma = vma_of(node);

if (!vma->vm_prev)
return vma->vm_start;

return vma->vm_start - vma->vm_prev->vm_end;
}

You can write your largest free gap as:

unsigned long largest_gap(struct rb_node *node)
{
unsigned long gap = gap_of(node);

if (node->rb_left)
gap = max(gap, max_gap_of(node->rb_left));
if (node->rb_right)
gap = max(gap, max_gap_of(node->rb_right));

return gap;
}

And as shown, you can re-used those {max_,}gap_of() function in the
lookup function in the next patch.


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