[PATCH 8/9] procfs: Use faster rb_first_cached()

Davidlohr Bueso
2017-06-29T17:18:14Z

... such that we can avoid the tree walks to get the
node with the smallest key. Semantically the same,
as the previously used rb_first(), but O(1). The
main overhead is the extra footprint for the cached
rb_node pointer, which should not matter for procfs.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
fs/proc/generic.c | 26 ++++++++++++++------------
fs/proc/internal.h | 2 +-
fs/proc/proc_net.c | 2 +-
fs/proc/root.c | 2 +-
4 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index e3cda0b5968f..ab6496356dc2 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -40,8 +40,8 @@ static int proc_match(unsigned int len, const char *name, struct proc_dir_entry

static struct proc_dir_entry *pde_subdir_first(struct proc_dir_entry *dir)
{
- return rb_entry_safe(rb_first(&dir->subdir), struct proc_dir_entry,
- subdir_node);
+ return rb_entry_safe(rb_first_cached(&dir->subdir),
+ struct proc_dir_entry, subdir_node);
}

static struct proc_dir_entry *pde_subdir_next(struct proc_dir_entry *dir)
@@ -54,7 +54,7 @@ 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;
+ struct rb_node *node = dir->subdir.rb_root.rb_node;

while (node) {
struct proc_dir_entry *de = rb_entry(node,
@@ -75,8 +75,9 @@ static struct proc_dir_entry *pde_subdir_find(struct proc_dir_entry *dir,
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;
+ struct rb_root_cached *root = &dir->subdir;
+ struct rb_node **new = &root->rb_root.rb_node, *parent = NULL;
+ bool leftmost = true;

/* Figure out where to put new node */
while (*new) {
@@ -88,15 +89,16 @@ static bool pde_subdir_insert(struct proc_dir_entry *dir,
parent = *new;
if (result < 0)
new = &(*new)->rb_left;
- else if (result > 0)
+ else if (result > 0) {
new = &(*new)->rb_right;
- else
+ leftmost = false;
+ } else
return false;
}

/* Add new node and rebalance tree. */
rb_link_node(&de->subdir_node, parent, new);
- rb_insert_color(&de->subdir_node, root);
+ rb_insert_color_cached(&de->subdir_node, root, leftmost);
return true;
}

@@ -369,7 +371,7 @@ 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;
+ ent->subdir = RB_ROOT_CACHED;
atomic_set(&ent->count, 1);
spin_lock_init(&ent->pde_unload_lock);
INIT_LIST_HEAD(&ent->pde_openers);
@@ -545,7 +547,7 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent)

de = pde_subdir_find(parent, fn, len);
if (de)
- rb_erase(&de->subdir_node, &parent->subdir);
+ rb_erase_cached(&de->subdir_node, &parent->subdir);
write_unlock(&proc_subdir_lock);
if (!de) {
WARN(1, "name '%s'\n", name);
@@ -582,13 +584,13 @@ int remove_proc_subtree(const char *name, struct proc_dir_entry *parent)
write_unlock(&proc_subdir_lock);
return -ENOENT;
}
- rb_erase(&root->subdir_node, &parent->subdir);
+ rb_erase_cached(&root->subdir_node, &parent->subdir);

de = root;
while (1) {
next = pde_subdir_first(de);
if (next) {
- rb_erase(&next->subdir_node, &de->subdir);
+ rb_erase_cached(&next->subdir_node, &de->subdir);
de = next;
continue;
}
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index 07b16318223f..4db394edb6d9 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -40,7 +40,7 @@ struct proc_dir_entry {
const struct inode_operations *proc_iops;
const struct file_operations *proc_fops;
struct proc_dir_entry *parent;
- struct rb_root subdir;
+ struct rb_root_cached subdir;
struct rb_node subdir_node;
void *data;
atomic_t count; /* use count */
diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index d72fc40241d9..a2bf369c923d 100644
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -196,7 +196,7 @@ static __net_init int proc_net_ns_init(struct net *net)
if (!netd)
goto out;

- netd->subdir = RB_ROOT;
+ netd->subdir = RB_ROOT_CACHED;
netd->data = net;
netd->nlink = 2;
netd->namelen = 3;
diff --git a/fs/proc/root.c b/fs/proc/root.c
index deecb397daa3..926fb27f4ca2 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -210,7 +210,7 @@ struct proc_dir_entry proc_root = {
.proc_iops = &proc_root_inode_operations,
.proc_fops = &proc_root_operations,
.parent = &proc_root,
- .subdir = RB_ROOT,
+ .subdir = RB_ROOT_CACHED,
.name = "/proc",
};

--
2.12.0