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

[Wei Yang]

On Sun, Oct 27, 2019 at 09:29:43PM -0700, Michel Lespinasse wrote:
>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 !
>

Thanks :-)

>Reviewed-By: Michel Lespinasse <walken@xxxxxxxxxx>
>
>On Sun, Oct 27, 2019 at 7:15 PM Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
>> ---
>>  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.

-- 
Wei Yang
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