Re: RCU red-black tree (was: Re: [PATCH 4/6] kvm tools: Add rwlock wrapper)

Sasha Levin
2011-05-30T17:53:21Z

On Mon, 2011-05-30 at 13:38 -0400, Mathieu Desnoyers wrote:
> * Sasha Levin (levinsasha928@gmail.com) wrote:
> > On Sun, 2011-05-29 at 22:54 -0400, Mathieu Desnoyers wrote:
> > > Please note that what I currently have is a normal rbtree, not an
> > > interval rbtree. Can you elaborate on your use-case so I can try to
> > > figure out how we could augment it to support the interval rbtree you
> > > need ?
> >
> > We don't need anything specific for interval rbtree. The rbtree used in
> > the kernel provides augmentation functions for insert and erase (see
> > rb_augment_insert() and rb_augment_erase_begin() +
> > rb_augment_erase_end()).
> > What they basically do is call a user-provided callback for each node
> > from the newly inserted (or deepest after deletion) node up to the root
> > of the tree. You can see our code at 'tools/kvm/util/rbtree-interval.c',
> > basically all we need are the 2 augmentation functions I've mentioned
> > above.
>
> Just a little question about Documentation/rbtree.txt:
>
> I see that find_lowest_match(lo, hi, node) seems to use ">" and "<" to
> compare the lo value with the max_hi and node->lo. I think it would be
> more natural to do range comparison functions with inclusive ranges (>=
> and <=). Or maybe I am missing something about the way find_lowest_match
> works ?

It's just an implementation of an interval search() function. Since
kernel rbtree users implement their own search() and insert() functions
(look in our util/rbtree-interval.c) it shouldn't be a consideration in
designing the tree - we (the users of urcu/rbtree) want to control the
search code anyway.

--

Sasha.