[PATCH linux v3 1/1] fs/proc: use a rb tree for the directory entries

From: Nicolas Dichtel
Date: Tue Oct 07 2014 - 05:03:07 EST

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 <thierry.herbelot@xxxxxxxxx>.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx>
Acked-by: David S. Miller <davem@xxxxxxxxxxxxx>
---
fs/proc/generic.c | 164 ++++++++++++++++++++++++++++++++++-------------------
fs/proc/internal.h | 11 ++--
fs/proc/proc_net.c | 1 +
fs/proc/root.c | 1 +
4 files changed, 113 insertions(+), 64 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;
}
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index 7da13e49128a..433557634c1b 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -24,10 +24,9 @@ struct mempolicy;
* tree) of these proc_dir_entries, so that we can dynamically
* add new files to /proc.
*
- * The "next" pointer creates a linked list of one /proc directory,
- * while parent/subdir create the directory structure (every
- * /proc file has a parent, but "subdir" is NULL for all
- * non-directory entries).
+ * parent/subdir are used for the directory structure (every /proc file has a
+ * parent, but "subdir" is empty for all non-directory entries).
+ * subdir_node is used to build the rb tree "subdir" of the parent.
*/
struct proc_dir_entry {
unsigned int low_ino;
@@ -38,7 +37,9 @@ struct proc_dir_entry {
loff_t size;
const struct inode_operations *proc_iops;
const struct file_operations *proc_fops;
- struct proc_dir_entry *next, *parent, *subdir;
+ struct proc_dir_entry *parent;
+ struct rb_root subdir;
+ struct rb_node subdir_node;
void *data;
atomic_t count; /* use count */
atomic_t in_use; /* number of callers into module in progress; */
diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index a63af3e0a612..1bde894bc624 100644
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -192,6 +192,7 @@ static __net_init int proc_net_ns_init(struct net *net)
if (!netd)
goto out;

+ netd->subdir = RB_ROOT;
netd->data = net;
netd->nlink = 2;
netd->namelen = 3;
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 094e44d4a6be..4eae849baedd 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -166,6 +166,7 @@ void __init proc_root_init(void)
{
int err;

+ proc_root.subdir = RB_ROOT;
proc_init_inodecache();
err = register_filesystem(&proc_fs_type);
if (err)
--
2.1.0

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