linux-kernel - Re: [PATCH 1/8] rbtree: Cache leftmost node internally

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Message-ID: <20170609143250.GB20320@linux-80c1.suse>
Date:   Fri, 9 Jun 2017 07:32:50 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Jan Kara <jack@...e.cz>
Cc:     mingo@...nel.org, peterz@...radead.org, akpm@...ux-foundation.org,
        kirill.shutemov@...ux.intel.com, ldufour@...ux.vnet.ibm.com,
        mhocko@...e.com, mgorman@...hsingularity.net,
        linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 1/8] rbtree: Cache leftmost node internally

On Fri, 09 Jun 2017, Jan Kara wrote:
>
>Looks good to me. Just one nit below:

Thanks for having a look!

>
>> @@ -150,6 +161,7 @@ extern void __rb_erase_color(struct rb_node *parent, struct rb_root *root,
>>
>>  static __always_inline struct rb_node *
>>  __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
>> +		     struct rb_node **leftmost,
>>  		     const struct rb_augment_callbacks *augment)
>>  {
>>  	struct rb_node *child = node->rb_right;
>> @@ -157,6 +169,9 @@ __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
>>  	struct rb_node *parent, *rebalance;
>>  	unsigned long pc;
>>
>> +	if (leftmost && node == *leftmost)
>> +		*leftmost = rb_next(node);
>> +
>>  	if (!tmp) {
>>  		/*
>>  		 * Case 1: node to erase has no more than 1 child (easy!)
>
>Why do you propagate e.g. 'leftmost' down to __rb_erase_augmented() when
>you could just handle everything within rb_erase_augmented_cached?
>Similarly for other functions like __rb_insert()... It would seem like less
>churn and I don't see downside to it...

I propagate args so we don't have to duplicate the checks between the regular
and augmented rbtrees.

Thanks,
Davidlohr