[dm-devel] [PATCH 2/4] sysfs: use rb-tree for name lookups

[Mikulas Patocka]

sysfs: use rb-tree for name lookups

Use red-black tree for name lookups.

This patch improves time to create 10000 block devices from 120 seconds to 
68 seconds.

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>

---
 fs/sysfs/dir.c   |   45 +++++++++++++++++++++++++++++++++++++++------
 fs/sysfs/sysfs.h |    5 +++++
 2 files changed, 44 insertions(+), 6 deletions(-)

Index: linux-3.0-rc7-fast/fs/sysfs/sysfs.h
===================================================================
--- linux-3.0-rc7-fast.orig/fs/sysfs/sysfs.h	2011-07-18 20:06:24.000000000 +0200
+++ linux-3.0-rc7-fast/fs/sysfs/sysfs.h	2011-07-18 20:16:32.000000000 +0200
@@ -11,6 +11,7 @@
 #include <linux/lockdep.h>
 #include <linux/kobject_ns.h>
 #include <linux/fs.h>
+#include <linux/rbtree.h>
 
 struct sysfs_open_dirent;
 
@@ -21,6 +22,8 @@ struct sysfs_elem_dir {
 	struct sysfs_dirent	*children;
 
 	unsigned long		subdirs;
+
+	struct rb_root		name_tree;
 };
 
 struct sysfs_elem_symlink {
@@ -61,6 +64,8 @@ struct sysfs_dirent {
 	struct sysfs_dirent	*s_sibling;
 	const char		*s_name;
 
+	struct rb_node		name_node;
+
 	const void		*s_ns; /* namespace tag */
 	union {
 		struct sysfs_elem_dir		s_dir;
Index: linux-3.0-rc7-fast/fs/sysfs/dir.c
===================================================================
--- linux-3.0-rc7-fast.orig/fs/sysfs/dir.c	2011-07-18 20:06:24.000000000 +0200
+++ linux-3.0-rc7-fast/fs/sysfs/dir.c	2011-07-18 20:16:02.000000000 +0200
@@ -45,6 +45,9 @@ static void sysfs_link_sibling(struct sy
 	struct sysfs_dirent *parent_sd = sd->s_parent;
 	struct sysfs_dirent **pos;
 
+	struct rb_node **p;
+	struct rb_node *parent;
+
 	BUG_ON(sd->s_sibling);
 
 	if (sysfs_type(sd) == SYSFS_DIR)
@@ -60,6 +63,26 @@ static void sysfs_link_sibling(struct sy
 	}
 	sd->s_sibling = *pos;
 	*pos = sd;
+
+	p = &parent_sd->s_dir.name_tree.rb_node;
+	parent = NULL;
+	while (*p) {
+		int c;
+		parent = *p;
+#define node	rb_entry(parent, struct sysfs_dirent, name_node)
+		c = strcmp(sd->s_name, node->s_name);
+		if (c < 0) {
+			p = &node->name_node.rb_left;
+		} else if (c > 0) {
+			p = &node->name_node.rb_right;
+		} else {
+			printk(KERN_CRIT "sysfs: inserting duplicate filename '%s'\n", sd->s_name);
+			BUG();
+		}
+#undef node
+	}
+	rb_link_node(&sd->name_node, parent, p);
+	rb_insert_color(&sd->name_node, &parent_sd->s_dir.name_tree);
 }
 
 /**
@@ -87,6 +110,8 @@ static void sysfs_unlink_sibling(struct 
 			break;
 		}
 	}
+
+	rb_erase(&sd->name_node, &sd->s_parent->s_dir.name_tree);
 }
 
 /**
@@ -546,14 +571,22 @@ struct sysfs_dirent *sysfs_find_dirent(s
 				       const void *ns,
 				       const unsigned char *name)
 {
-	struct sysfs_dirent *sd;
+	struct rb_node *p = parent_sd->s_dir.name_tree.rb_node;
 
-	for (sd = parent_sd->s_dir.children; sd; sd = sd->s_sibling) {
-		if (ns && sd->s_ns && (sd->s_ns != ns))
-			continue;
-		if (!strcmp(sd->s_name, name))
-			return sd;
+	while (p) {
+		int c;
+#define node	rb_entry(p, struct sysfs_dirent, name_node)
+		c = strcmp(name, node->s_name);
+		if (c < 0) {
+			p = node->name_node.rb_left;
+		} else if (c > 0) {
+			p = node->name_node.rb_right;
+		} else {
+			return node;
+		}
+#undef node
 	}
+
 	return NULL;
 }