procfs: use faster rb_first_cached()

...  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.

Link: http://lkml.kernel.org/r/20170719014603.19029-14-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 17 insertions, 15 deletions

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 85566abe6f83..793a67574668 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);
@@ -553,7 +555,7 @@ 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);
@@ -590,13 +592,13 @@ 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 2cbfcd32e884..a34195e92b20 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",
 };