Re: [PATCH 1/8] rbtree: Cache leftmost node internally

[Davidlohr Bueso]

On Fri, 09 Jun 2017, Jan Kara wrote:
> Looks good to me. Just one nit below:

Thanks for having a look!

> > @@ -150,6 +161,7 @@ extern void __rb_erase_color(struct rb_node *parent, struct rb_root *root,
> >
> >  static __always_inline struct rb_node *
> >  __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
> > +		     struct rb_node **leftmost,
> >  		     const struct rb_augment_callbacks *augment)
> >  {
> >  	struct rb_node *child = node->rb_right;
> > @@ -157,6 +169,9 @@ __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
> >  	struct rb_node *parent, *rebalance;
> >  	unsigned long pc;
> >
> > +	if (leftmost && node == *leftmost)
> > +		*leftmost = rb_next(node);
> > +
> >  	if (!tmp) {
> >  		/*
> >  		 * Case 1: node to erase has no more than 1 child (easy!)
>
> Why do you propagate e.g. 'leftmost' down to __rb_erase_augmented() when
> you could just handle everything within rb_erase_augmented_cached?
> Similarly for other functions like __rb_insert()... It would seem like less
> churn and I don't see downside to it...

I propagate args so we don't have to duplicate the checks between the regular
and augmented rbtrees.

Thanks,
Davidlohr