From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx125.postini.com [74.125.245.125]) by kanga.kvack.org (Postfix) with SMTP id CCD826B0068 for ; Thu, 12 Jul 2012 10:13:04 -0400 (EDT) Message-ID: <1342102376.28010.7.camel@twins> Subject: Re: [PATCH 00/13] rbtree updates From: Peter Zijlstra Date: Thu, 12 Jul 2012 16:12:56 +0200 In-Reply-To: <20120712011208.GA1152@google.com> References: <1341876923-12469-1-git-send-email-walken@google.com> <1342012996.3462.154.camel@twins> <20120712011208.GA1152@google.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable Mime-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Michel Lespinasse Cc: aarcange@redhat.com, dwmw2@infradead.org, riel@redhat.com, daniel.santos@pobox.com, axboe@kernel.dk, ebiederm@xmission.com, linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org On Wed, 2012-07-11 at 18:12 -0700, Michel Lespinasse wrote: >=20 > In __rb_erase_color(), some of the cases are more complicated than you dr= ew 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.. > This is what I ended up with: >=20 > * 5), then the longest possible path due to 4 is 2B. > * > * We shall indicate color with case, where black nodes are uppercase a= nd red > - * nodes will be lowercase. > + * nodes will be lowercase. Unknown color nodes shall be drawn as red w= ith > + * some accompanying text comment. > */ >=20 > + /* > + * Case 2 - sibling color flip > + * (p could be either color here) > + * > + * p p > + * / \ / \ > + * N S --> N s > + * / \ / \ > + * Sl Sr Sl Sr > + * > + * This leaves us violating 5), s= o > + * recurse at p. If p is red, the > + * recursion will just flip it to= black > + * and exit. If coming from Case = 1, > + * p is known to be red. > + */ >=20 > + /* > + * Case 3 - right rotate at sibling > + * (p could be either color here) > + * > + * p p > + * / \ / \ > + * N S --> N Sl > + * / \ \ > + * sl Sr s > + * \ > + * Sr > + */ >=20 > + /* > + * Case 4 - left rotate at parent + color flips > + * (p and sl could be either color here. > + * After rotation, p becomes black, s acquires > + * p's color, and sl keeps its color) > + * > + * p s > + * / \ / \ > + * N S --> P Sr > + * / \ / \ > + * sl sr N sl > + */=20 Yes, very nice.. someday when I'm bored I might expand the comments with the reason why we're doing the given operation. Also, I was sorely tempted to rename your tmp1,tmp2 variables to sl and sr. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org