Re: [PATCH] maple_tree: Avoid checking other gaps after getting the largest gap

[Peng Zhang]

在 2023/12/19 04:28, Liam R. Howlett 写道:
> * Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> [231218 15:20]:
> > * Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx> [231215 02:46]:
> > > The last range stored in maple tree is typically quite large. By
> > > checking if it exceeds the sum of the remaining ranges in that node, it
> > > is possible to avoid checking all other gaps.
> > >
> > > Running the maple tree test suite in user mode almost always results in
> > > a near 100% hit rate for this optimization.
> >
> > This should only be triggered for right-most nodes and root though,
> > correct (mas->max  == ULONG_MAX from just before this)?
Yes, only for right-most nodes and root.
> > I wonder if it's worth special case checking the first gap if the node
> > min is 0 as well.  Might be worth looking at, but this patch is
> > certainly worth doing.
>
> Actually, not just when the min is 0, we have a special case close to
> here for slot 0 so we could just check the same sort of thing there.
I think that the first slot in a node does not have any special
significance. It has a lower probability of being the largest gap,
so it may not be worth considering.
> > > Signed-off-by: Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx>
> >
> > Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> >
> > > ---
> > >   lib/maple_tree.c | 3 +++
> > >   1 file changed, 3 insertions(+)
> > >
> > > diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> > > index c9a970ea20dd..6f241bb38799 100644
> > > --- a/lib/maple_tree.c
> > > +++ b/lib/maple_tree.c
> > > @@ -1518,6 +1518,9 @@ static unsigned long mas_leaf_max_gap(struct ma_state *mas)
> > >   		gap = ULONG_MAX - pivots[max_piv];
> > >   		if (gap > max_gap)
> > >   			max_gap = gap;
> > > +
> > > +		if (max_gap > pivots[max_piv] - mas->min)
> > > +			return max_gap;
> > >   	}
> > >   
> > >   	for (; i <= max_piv; i++) {
> > > --
> > > 2.20.1