linux-kernel - Re: [PATCH] rbtree: undo augmented damage -v2

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Message-ID: <AANLkTilGfY1PnNgpEeB3AQEqTNoDJQfPTxK5LNUYb7ZA@mail.gmail.com>
Date:	Tue, 1 Jun 2010 10:34:31 -0700
From:	Venkatesh Pallipadi <venki@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	suresh.b.siddha@...el.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org,
	Fabio Checconi <fabio@...dalf.sssup.it>
Subject: Re: [PATCH] rbtree: undo augmented damage -v2

On Tue, Jun 1, 2010 at 10:19 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, 2010-06-01 at 10:00 -0700, Venkatesh Pallipadi wrote:
>> I am not seeing how this can cover all the callbacks we will need to
>> maintain the augmented tree property. May be I am missing something.
>
> Yes, indeed, how about the below delta, which my eevdf code did do but I
> overlooked on the conversion to the PAT code.
>
> That removes the break as you said, but also adds code to update the
> child nodes when walking up the path.
>
> So in your rotation case:
>
>    G             P
>   / \    -->    / \
>  P   U         N   G
>  /        <--        \
> N                     U
>
> Say we take the right rotation, then the traversal up from N to P will
> find that since N was the left child of P and it has a right child (G)
> it will also update G.

Yes. This will cover all the cases on insert. But on erase, there is
still a case where a rotate of sibling node is done during the
re-coloration process. There we have a child change on sibling's
child. I am not able to think of any easy way to handle that case.

Thanks,
Venki

>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  arch/x86/mm/pat_rbtree.c |   23 ++++++++++++-----------
>  1 files changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/mm/pat_rbtree.c b/arch/x86/mm/pat_rbtree.c
> index f537087..ca19aae 100644
> --- a/arch/x86/mm/pat_rbtree.c
> +++ b/arch/x86/mm/pat_rbtree.c
> @@ -81,20 +81,21 @@ static void update_node_max_end(struct rb_node *node)
>  /* Update 'subtree_max_end' for a node and all its ancestors */
>  static void update_path_max_end(struct rb_node *node)
>  {
> -       u64 old_max_end, new_max_end;
> +       struct rb_node *parent;
>
> -       while (node) {
> -               struct memtype *data = container_of(node, struct memtype, rb);
> -
> -               old_max_end = data->subtree_max_end;
> -               update_node_max_end(node);
> -               new_max_end = data->subtree_max_end;
> +up:
> +       update_node_max_end(node);
> +       parent = rb_parent(node);
> +       if (!parent)
> +               return;
>
> -               if (new_max_end == old_max_end)
> -                       break;
> +       if (node == parent->rb_left && parent->rb_right)
> +               update_node_max_end(parent->rb_right);
> +       else if (parent->rb_left)
> +               update_node_max_end(parent->rb_left);
>
> -               node = rb_parent(node);
> -       }
> +       node = parent;
> +       goto up;
>  }
>
>  /* Find the first (lowest start addr) overlapping range from rb tree */
>
>
--
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