linux-kernel - Re: [Patch v2 1/2] lib/rbtree: set successor's parent unconditionally

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Date:   Sun, 27 Oct 2019 21:29:43 -0700
From:   Michel Lespinasse <walken@...gle.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Davidlohr Bueso <dbueso@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Patch v2 1/2] lib/rbtree: set successor's parent unconditionally

Code looks fine, for both commits in this series. Please make sure to
double check that lib/rbtree_test does not show any performance
regressions, but assuming they don't, looks great !

Reviewed-By: Michel Lespinasse <walken@...gle.com>

On Sun, Oct 27, 2019 at 7:15 PM Wei Yang <richardw.yang@...ux.intel.com> wrote:
>
> Both in Case 2 and 3, we exchange n and s. This mean no matter whether
> child2 is NULL or not, successor's parent should be assigned to node's.
>
> This patch takes this step out to make it explicit and reduce the
> ambiguity.
>
> Besides, this step reduces some symbol size like rb_erase().
>
>    KERN_CONFIG       upstream       patched
>    OPT_FOR_PERF      877            870
>    OPT_FOR_SIZE      635            621
>
> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
> ---
>  include/linux/rbtree_augmented.h | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/include/linux/rbtree_augmented.h b/include/linux/rbtree_augmented.h
> index fdd421b8d9ae..99c42e1a74b8 100644
> --- a/include/linux/rbtree_augmented.h
> +++ b/include/linux/rbtree_augmented.h
> @@ -283,14 +283,13 @@ __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
>                 __rb_change_child(node, successor, tmp, root);
>
>                 if (child2) {
> -                       successor->__rb_parent_color = pc;
>                         rb_set_parent_color(child2, parent, RB_BLACK);
>                         rebalance = NULL;
>                 } else {
>                         unsigned long pc2 = successor->__rb_parent_color;
> -                       successor->__rb_parent_color = pc;
>                         rebalance = __rb_is_black(pc2) ? parent : NULL;
>                 }
> +               successor->__rb_parent_color = pc;
>                 tmp = successor;
>         }
>
> --
> 2.17.1
>


-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.