[PATCH] proc: faster /proc/$PID lookup

[Alexey Dobriyan <adobriyan@gmail.com>]

Use first character as a hint for /proc/$PID lookup.

Currently it takes one spinlock and search through dozens of
misc proc entries which can not match /proc/$PID.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 fs/proc/root.c |   15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -199,10 +199,17 @@ static int proc_root_getattr(struct vfsmount *mnt, struct dentry *dentry, struct
 
 static struct dentry *proc_root_lookup(struct inode * dir, struct dentry * dentry, unsigned int flags)
 {
-	if (!proc_lookup(dir, dentry, flags))
-		return NULL;
-	
-	return proc_pid_lookup(dir, dentry, flags);
+	const char c = dentry->d_name.name[0];
+	struct dentry *rv;
+
+	if ('0' <= c && c <= '9') {
+		rv = proc_pid_lookup(dir, dentry, flags);
+		if (rv)
+			rv = proc_lookup(dir, dentry, flags);
+	} else {
+		rv = proc_lookup(dir, dentry, flags);
+	}
+	return rv;
 }
 
 static int proc_root_readdir(struct file *file, struct dir_context *ctx)