linux-kernel - [PATCH 03/17] rbtree: add some additional comments for rebalancing cases

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Message-Id: <20170719014603.19029-4-dave@stgolabs.net>
Date:   Tue, 18 Jul 2017 18:45:49 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     akpm@...ux-foundation.org
Cc:     mingo@...nel.org, peterz@...radead.org, jack@...e.cz,
        torvalds@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        hch@...radead.org, ldufour@...ux.vnet.ibm.com, mhocko@...e.com,
        mgorman@...hsingularity.net, dave@...olabs.net,
        linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 03/17] rbtree: add some additional comments for rebalancing cases

While overall the code is very nicely commented, it might not be
immediately obvious from the diagrams what is going on. Add a
very brief summary of each case. Opposite cases where the node
is the left child are left untouched.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 lib/rbtree.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/rbtree.c b/lib/rbtree.c
index e7cce12f404f..ba4a9d165f1b 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -132,7 +132,7 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
 		if (parent != tmp) {	/* parent == gparent->rb_left */
 			if (tmp && rb_is_red(tmp)) {
 				/*
-				 * Case 1 - color flips
+				 * Case 1 - node's uncle is red (color flips).
 				 *
 				 *       G            g
 				 *      / \          / \
@@ -155,7 +155,8 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
 			tmp = parent->rb_right;
 			if (node == tmp) {
 				/*
-				 * Case 2 - left rotate at parent
+				 * Case 2 - node's uncle is black and node is
+				 * the parent's right child (left rotate at parent).
 				 *
 				 *      G             G
 				 *     / \           / \
@@ -179,7 +180,8 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
 			}
 
 			/*
-			 * Case 3 - right rotate at gparent
+			 * Case 3 - node's uncle is black and node is
+			 * the parent's left child (right rotate at gparent).
 			 *
 			 *        G           P
 			 *       / \         / \
-- 
2.12.0