linux-kernel - Re: [PATCH v3 2/3] augmented rbtree: add new RB_DECLARE_CALLBACKS

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Date:   Tue, 30 Jul 2019 00:31:04 -0700
From:   Michel Lespinasse <walken@...gle.com>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Peter Zijlstra <peterz@...radead.org>,
        David Howells <dhowells@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/3] augmented rbtree: add new RB_DECLARE_CALLBACKS_MAX macro

On Mon, Jul 29, 2019 at 3:15 AM Uladzislau Rezki <urezki@...il.com> wrote:
>
> >
> > --- a/lib/rbtree_test.c~augmented-rbtree-add-new-rb_declare_callbacks_max-macro-fix-2
> > +++ a/lib/rbtree_test.c
> > @@ -220,10 +220,6 @@ static void check_augmented(int nr_nodes
> >       struct rb_node *rb;
> >
> >       check(nr_nodes);
> > -     for (rb = rb_first(&root.rb_root); rb; rb = rb_next(rb)) {
> > -             struct test_node *node = rb_entry(rb, struct test_node, rb);
> > -             WARN_ON_ONCE(node->augmented != augment_recompute(node));
> > -     }
> >  }
> >
> I have a question here it is a bit out of this topic but still related :)
>
> Can we move "check augmented" functionality to the rbtree_augmented.h
> header file making it public?

Hmmm, I had not thought about that. Agree that this can be useful -
there is already similar test code in rbtree_test.c and also
vma_compute_subtree_gap() in mmap.c, ...

With patch 3/3 of this series, the RBCOMPUTE function (typically
generated through the RB_DECLARE_CALLBACKS_MAX macro) will return a
bool indicating if the node's augmented value was already correctly
set. Maybe this can be used for test code, through in the false case,
the node's augmented value is already overwritten with the correct
value. Not sure if that is a problem though - the files I mentioned
above have test code that will dump the values if there is a mismatch,
but really I think in every realistic case just noting that there was
one would be just as helpful as being able to dump the old (incorrect)
value....

What do you think - is the RBCOMPUTE(node, true) function sufficient
for such debugging ?