* Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx> [230419 05:02]:
>
> 在 2023/4/14 22:57, Liam R. Howlett 写道:
> > Stop using maple state min/max for the range by passing through pointers
> > for those values. This will allow the maple state to be reused without
> > resetting.
> >
> > Also add some logic to fail out early on searching with invalid
> > arguments.
> >
> > Fixes: 54a611b60590 ("Maple Tree: add new data structure")
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> > ---
> > lib/maple_tree.c | 27 +++++++++++++--------------
> > 1 file changed, 13 insertions(+), 14 deletions(-)
> >
> > diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> > index 4df6a0ce1c1b..ed350aa293b2 100644
> > --- a/lib/maple_tree.c
> > +++ b/lib/maple_tree.c
> > @@ -4938,7 +4938,8 @@ static inline void *mas_prev_entry(struct ma_state *mas, unsigned long min)
> > * Return: True if found in a leaf, false otherwise.
> > *
> > */
> > -static bool mas_rev_awalk(struct ma_state *mas, unsigned long size)
> > +static bool mas_rev_awalk(struct ma_state *mas, unsigned long size,
> > + unsigned long *gap_min, unsigned long *gap_max)
> > {
> > enum maple_type type = mte_node_type(mas->node);
> > struct maple_node *node = mas_mn(mas);
> > @@ -5003,8 +5004,8 @@ static bool mas_rev_awalk(struct ma_state *mas, unsigned long size)
> > if (unlikely(ma_is_leaf(type))) {
> > mas->offset = offset;
> > - mas->min = min;
> > - mas->max = min + gap - 1;
> > + *gap_min = min;
> > + *gap_max = min + gap - 1;
> > return true;
> > }
> > @@ -5280,6 +5281,9 @@ int mas_empty_area(struct ma_state *mas, unsigned long min,
> > unsigned long *pivots;
> > enum maple_type mt;
> > + if (min >= max)
> This can lead to errors, min == max is valid.
> I think it's better to change it to this:
> if (min > max || size == 0 || max - min < size - 1)
I am not sure what it means to search within a range of one. I guess
you would expect it to just return that value if it's empty?
In any case, since we are dealing with pages of data for the VMAs,
having min == max really makes no sense, even with the subtraction of
one in the caller to reduce the max, the min and max should be at least
PAGE_SIZE - 1 apart here.
I think you are right, and I think this needs to be looked at for the
tree on its own, but I don't think it's a problem for the VMA user. I'll
write a testcase and ensure a search for a single entry in a single
entry window works separately. Thanks for pointing this out.
> > + return -EINVAL;
> > +
> > if (mas_is_start(mas))
> > mas_start(mas);
> > else if (mas->offset >= 2)
> > @@ -5334,6 +5338,9 @@ int mas_empty_area_rev(struct ma_state *mas, unsigned long min,
> > {
> > struct maple_enode *last = mas->node;
> > + if (min >= max)
> ditto.
I'll do the search in both directions.
> > + return -EINVAL;
> > +
> > if (mas_is_start(mas)) {
> > mas_start(mas);
> > mas->offset = mas_data_end(mas);
> > @@ -5353,7 +5360,7 @@ int mas_empty_area_rev(struct ma_state *mas, unsigned long min,
> > mas->index = min;
> > mas->last = max;
> > - while (!mas_rev_awalk(mas, size)) {
> > + while (!mas_rev_awalk(mas, size, &min, &max)) {
> > if (last == mas->node) {
> > if (!mas_rewind_node(mas))
> > return -EBUSY;
> > @@ -5368,17 +5375,9 @@ int mas_empty_area_rev(struct ma_state *mas, unsigned long min,
> > if (unlikely(mas->offset == MAPLE_NODE_SLOTS))
> > return -EBUSY;
> > - /*
> > - * mas_rev_awalk() has set mas->min and mas->max to the gap values. If
> > - * the maximum is outside the window we are searching, then use the last
> > - * location in the search.
> > - * mas->max and mas->min is the range of the gap.
> > - * mas->index and mas->last are currently set to the search range.
> > - */
> > -
> > /* Trim the upper limit to the max. */
> > - if (mas->max <= mas->last)
> > - mas->last = mas->max;
> > + if (max <= mas->last)
> > + mas->last = max;
>
> We can get max as follows, without using pointers to track min, max in
> mas_rev_awalk().
>
> mt = mte_node_type(mas->node); pivots = ma_pivots(mas_mn(mas), mt); max =
> mas_logical_pivot(mas, pivots, mas->offset, mt);
Yes, but why would we do this? We have done all this work already in
mas_rev_awalk(), and we have to do it there to get the offset in the
first place.
> if (max < mas->last) /* The equal sign here can be removed */
Thanks. I'll keep this in mind when I revisit the function. I don't
want to re-spin the patch for this alone.
> mas->last = max;
>
> > mas->index = mas->last - size + 1;
> > return 0;
