linux-kernel - Re: [PATCH 00/13] rbtree updates

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Message-ID: <CANN689GdKaACaCcvuFym5qp=QJEMRVmK1qzmV4PpyfxLYCgk+A@mail.gmail.com>
Date:	Thu, 12 Jul 2012 17:39:27 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	aarcange@...hat.com, dwmw2@...radead.org, riel@...hat.com,
	daniel.santos@...ox.com, axboe@...nel.dk, ebiederm@...ssion.com,
	linux-mm@...ck.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org
Subject: Re: [PATCH 00/13] rbtree updates

On Thu, Jul 12, 2012 at 7:12 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, 2012-07-11 at 18:12 -0700, Michel Lespinasse wrote:
>>
>> In __rb_erase_color(), some of the cases are more complicated than you drew however, because some node colors aren't known.
>
> Right, the wikipedia article draws them blank, I couldn't come up with a
> 3rd case, although maybe we can annotate them like (P) to mean blank..

Ah, good idea, I adopted that :)

> Yes, very nice.. someday when I'm bored I might expand the comments with
> the reason why we're doing the given operation.

There is a brief comment at the start of the loop that indicates which
rbtree invariants might be violated at that point; so someone could
deduce that we're trying to either fix these or move towards the root
until they get fixed. But yeah, this is never explicitly explained.

> Also, I was sorely tempted to rename your tmp1,tmp2 variables to sl and
> sr.

This could be done, but you'd *still* need one extra temporary, so
you'd end up with sl, sr and tmp. Which is fine, I guess, but I
preferred to have one less variable around.

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