fs/proc: use a rb tree for the directory entries

When a lot of netdevices are created, one of the bottleneck is the
creation of proc entries.  This serie aims to accelerate this part.

The current implementation for the directories in /proc is using a single
linked list.  This is slow when handling directories with large numbers of
entries (eg netdevice-related entries when lots of tunnels are opened).

This patch replaces this linked list by a red-black tree.

Here are some numbers:

dummy30000.batch contains 30 000 times 'link add type dummy'.

Before the patch:
  $ time ip -b dummy30000.batch
  real    2m31.950s
  user    0m0.440s
  sys     2m21.440s
  $ time rmmod dummy
  real    1m35.764s
  user    0m0.000s
  sys     1m24.088s

After the patch:
  $ time ip -b dummy30000.batch
  real    2m0.874s
  user    0m0.448s
  sys     1m49.720s
  $ time rmmod dummy
  real    1m13.988s
  user    0m0.000s
  sys     1m1.008s

The idea of improving this part was suggested by Thierry Herbelot.

[akpm@linux-foundation.org: initialise proc_root.subdir at compile time]
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: David S. Miller <davem@davemloft.net>
Cc: Thierry Herbelot <thierry.herbelot@6wind.com>.
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 105 insertions, 59 deletions

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 317b72641ebf..9f8fa1e5e8aa 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -31,9 +31,81 @@ static DEFINE_SPINLOCK(proc_subdir_lock);
 
 static int proc_match(unsigned int len, const char *name, struct proc_dir_entry *de)
 {
-        if (de->namelen != len)
-                return 0;
-        return !memcmp(name, de->name, len);
+        if (len < de->namelen)
+                return -1;
+        if (len > de->namelen)
+                return 1;
+
+        return memcmp(name, de->name, len);
+}
+
+static struct proc_dir_entry *pde_subdir_first(struct proc_dir_entry *dir)
+{
+        struct rb_node *node = rb_first(&dir->subdir);
+
+        if (node == NULL)
+                return NULL;
+
+        return rb_entry(node, struct proc_dir_entry, subdir_node);
+}
+
+static struct proc_dir_entry *pde_subdir_next(struct proc_dir_entry *dir)
+{
+        struct rb_node *node = rb_next(&dir->subdir_node);
+
+        if (node == NULL)
+                return NULL;
+
+        return rb_entry(node, struct proc_dir_entry, subdir_node);
+}
+
+static struct proc_dir_entry *pde_subdir_find(struct proc_dir_entry *dir,
+                                              const char *name,
+                                              unsigned int len)
+{
+        struct rb_node *node = dir->subdir.rb_node;
+
+        while (node) {
+                struct proc_dir_entry *de = container_of(node,
+                                                         struct proc_dir_entry,
+                                                         subdir_node);
+                int result = proc_match(len, name, de);
+
+                if (result < 0)
+                        node = node->rb_left;
+                else if (result > 0)
+                        node = node->rb_right;
+                else
+                        return de;
+        }
+        return NULL;
+}
+
+static bool pde_subdir_insert(struct proc_dir_entry *dir,
+                              struct proc_dir_entry *de)
+{
+        struct rb_root *root = &dir->subdir;
+        struct rb_node **new = &root->rb_node, *parent = NULL;
+
+        /* Figure out where to put new node */
+        while (*new) {
+                struct proc_dir_entry *this =
+                        container_of(*new, struct proc_dir_entry, subdir_node);
+                int result = proc_match(de->namelen, de->name, this);
+
+                parent = *new;
+                if (result < 0)
+                        new = &(*new)->rb_left;
+                else if (result > 0)
+                        new = &(*new)->rb_right;
+                else
+                        return false;
+        }
+
+        /* Add new node and rebalance tree. */
+        rb_link_node(&de->subdir_node, parent, new);
+        rb_insert_color(&de->subdir_node, root);
+        return true;
 }
 
 static int proc_notify_change(struct dentry *dentry, struct iattr *iattr)
@@ -92,10 +164,7 @@ static int __xlate_proc_name(const char *name, struct proc_dir_entry **ret,
                         break;
 
                 len = next - cp;
-                for (de = de->subdir; de ; de = de->next) {
-                        if (proc_match(len, cp, de))
-                                break;
-                }
+                de = pde_subdir_find(de, cp, len);
                 if (!de) {
                         WARN(1, "name '%s'\n", name);
                         return -ENOENT;
@@ -183,19 +252,16 @@ struct dentry *proc_lookup_de(struct proc_dir_entry *de, struct inode *dir,
         struct inode *inode;
 
         spin_lock(&proc_subdir_lock);
-        for (de = de->subdir; de ; de = de->next) {
-                if (de->namelen != dentry->d_name.len)
-                        continue;
-                if (!memcmp(dentry->d_name.name, de->name, de->namelen)) {
-                        pde_get(de);
-                        spin_unlock(&proc_subdir_lock);
-                        inode = proc_get_inode(dir->i_sb, de);
-                        if (!inode)
-                                return ERR_PTR(-ENOMEM);
-                        d_set_d_op(dentry, &simple_dentry_operations);
-                        d_add(dentry, inode);
-                        return NULL;
-                }
+        de = pde_subdir_find(de, dentry->d_name.name, dentry->d_name.len);
+        if (de) {
+                pde_get(de);
+                spin_unlock(&proc_subdir_lock);
+                inode = proc_get_inode(dir->i_sb, de);
+                if (!inode)
+                        return ERR_PTR(-ENOMEM);
+                d_set_d_op(dentry, &simple_dentry_operations);
+                d_add(dentry, inode);
+                return NULL;
         }
         spin_unlock(&proc_subdir_lock);
         return ERR_PTR(-ENOENT);
@@ -225,7 +291,7 @@ int proc_readdir_de(struct proc_dir_entry *de, struct file *file,
                 return 0;
 
         spin_lock(&proc_subdir_lock);
-        de = de->subdir;
+        de = pde_subdir_first(de);
         i = ctx->pos - 2;
         for (;;) {
                 if (!de) {
@@ -234,7 +300,7 @@ int proc_readdir_de(struct proc_dir_entry *de, struct file *file,
                 }
                 if (!i)
                         break;
-                de = de->next;
+                de = pde_subdir_next(de);
                 i--;
         }
 
@@ -249,7 +315,7 @@ int proc_readdir_de(struct proc_dir_entry *de, struct file *file,
                 }
                 spin_lock(&proc_subdir_lock);
                 ctx->pos++;
-                next = de->next;
+                next = pde_subdir_next(de);
                 pde_put(de);
                 de = next;
         } while (de);
@@ -286,9 +352,8 @@ static const struct inode_operations proc_dir_inode_operations = {
 
 static int proc_register(struct proc_dir_entry * dir, struct proc_dir_entry * dp)
 {
-        struct proc_dir_entry *tmp;
         int ret;
-        
+
         ret = proc_alloc_inum(&dp->low_ino);
         if (ret)
                 return ret;
@@ -308,17 +373,10 @@ static int proc_register(struct proc_dir_entry * dir, struct proc_dir_entry * dp
         }
 
         spin_lock(&proc_subdir_lock);
-
-        for (tmp = dir->subdir; tmp; tmp = tmp->next)
-                if (strcmp(tmp->name, dp->name) == 0) {
-                        WARN(1, "proc_dir_entry '%s/%s' already registered\n",
-                                dir->name, dp->name);
-                        break;
-                }
-
-        dp->next = dir->subdir;
         dp->parent = dir;
-        dir->subdir = dp;
+        if (pde_subdir_insert(dir, dp) == false)
+                WARN(1, "proc_dir_entry '%s/%s' already registered\n",
+                     dir->name, dp->name);
         spin_unlock(&proc_subdir_lock);
 
         return 0;
@@ -354,6 +412,7 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
         ent->namelen = qstr.len;
         ent->mode = mode;
         ent->nlink = nlink;
+        ent->subdir = RB_ROOT;
         atomic_set(&ent->count, 1);
         spin_lock_init(&ent->pde_unload_lock);
         INIT_LIST_HEAD(&ent->pde_openers);
@@ -485,7 +544,6 @@ void pde_put(struct proc_dir_entry *pde)
  */
 void remove_proc_entry(const char *name, struct proc_dir_entry *parent)
 {
-        struct proc_dir_entry **p;
         struct proc_dir_entry *de = NULL;
         const char *fn = name;
         unsigned int len;
@@ -497,14 +555,9 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent)
         }
         len = strlen(fn);
 
-        for (p = &parent->subdir; *p; p=&(*p)->next ) {
-                if (proc_match(len, fn, *p)) {
-                        de = *p;
-                        *p = de->next;
-                        de->next = NULL;
-                        break;
-                }
-        }
+        de = pde_subdir_find(parent, fn, len);
+        if (de)
+                rb_erase(&de->subdir_node, &parent->subdir);
         spin_unlock(&proc_subdir_lock);
         if (!de) {
                 WARN(1, "name '%s'\n", name);
@@ -516,16 +569,15 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent)
         if (S_ISDIR(de->mode))
                 parent->nlink--;
         de->nlink = 0;
-        WARN(de->subdir, "%s: removing non-empty directory "
-                         "'%s/%s', leaking at least '%s'\n", __func__,
-                         de->parent->name, de->name, de->subdir->name);
+        WARN(pde_subdir_first(de),
+             "%s: removing non-empty directory '%s/%s', leaking at least '%s'\n",
+             __func__, de->parent->name, de->name, pde_subdir_first(de)->name);
         pde_put(de);
 }
 EXPORT_SYMBOL(remove_proc_entry);
 
 int remove_proc_subtree(const char *name, struct proc_dir_entry *parent)
 {
-        struct proc_dir_entry **p;
         struct proc_dir_entry *root = NULL, *de, *next;
         const char *fn = name;
         unsigned int len;
@@ -537,24 +589,18 @@ int remove_proc_subtree(const char *name, struct proc_dir_entry *parent)
         }
         len = strlen(fn);
 
-        for (p = &parent->subdir; *p; p=&(*p)->next ) {
-                if (proc_match(len, fn, *p)) {
-                        root = *p;
-                        *p = root->next;
-                        root->next = NULL;
-                        break;
-                }
-        }
+        root = pde_subdir_find(parent, fn, len);
         if (!root) {
                 spin_unlock(&proc_subdir_lock);
                 return -ENOENT;
         }
+        rb_erase(&root->subdir_node, &parent->subdir);
+
         de = root;
         while (1) {
-                next = de->subdir;
+                next = pde_subdir_first(de);
                 if (next) {
-                        de->subdir = next->next;
-                        next->next = NULL;
+                        rb_erase(&next->subdir_node, &de->subdir);
                         de = next;
                         continue;
                 }