From: NeilBrown <neilb@suse.de>
Subject: Make selection of 'readdir-plus' adapt to usage patterns.
Patch-mainline: not yet
References: bnc#678123

While the use of READDIRPLUS is significantly more efficient than
READDIR followed by many GETATTR calls, it is still less efficient
than just READDIR if the attributes are not required.

We can get a hint as to whether the application requires attr information
by looking at whether any ->getattr calls are made between
->readdir calls.  
If there are any, then getting the attributes seems to be worth while.

This patch tracks whether there have been recent getattr calls on
children of a directory and uses that information to selectively
disable READDIRPLUS on that directory.

The first 'readdir' call is always served using READDIRPLUS.
Subsequent calls only use READDIRPLUS if there was a getattr on a child
in the mean time.

The locking of ->d_parent access needs to be reviewed.
As the bit is simply a hint, it isn't critical that it is set
on the "correct" parent if a rename is happening, but it is
critical that the 'set' doesn't set a bit in something that
isn't even an inode any more.

Acked-by: NeilBrown <neilb@suse.de>
Signed-off-by: Neil Brown <neilb@suse.de>

---
 fs/nfs/dir.c           |    3 +++
 fs/nfs/inode.c         |    9 +++++++++
 include/linux/nfs_fs.h |    4 ++++
 3 files changed, 16 insertions(+)

--- linux-2.6.37-openSUSE-11.4.orig/fs/nfs/dir.c
+++ linux-2.6.37-openSUSE-11.4/fs/nfs/dir.c
@@ -802,6 +802,9 @@ static int nfs_readdir(struct file *filp
 	desc->dir_cookie = &dir_ctx->dir_cookie;
 	desc->decode = NFS_PROTO(inode)->decode_dirent;
 	desc->plus = NFS_USE_READDIRPLUS(inode);
+	if (filp->f_pos > 0 && !test_bit(NFS_INO_SEEN_GETATTR, &NFS_I(inode)->flags))
+		desc->plus = 0;
+	clear_bit(NFS_INO_SEEN_GETATTR, &NFS_I(inode)->flags);
 
 	nfs_block_sillyrename(dentry);
 	res = nfs_revalidate_mapping(inode, filp->f_mapping);
--- linux-2.6.37-openSUSE-11.4.orig/fs/nfs/inode.c
+++ linux-2.6.37-openSUSE-11.4/fs/nfs/inode.c
@@ -500,6 +500,15 @@ int nfs_getattr(struct vfsmount *mnt, st
 	struct inode *inode = dentry->d_inode;
 	int need_atime = NFS_I(inode)->cache_validity & NFS_INO_INVALID_ATIME;
 	int err;
+	struct dentry *p;
+	struct inode *pi;
+
+	rcu_read_lock();
+	p = dentry->d_parent;
+	pi = rcu_dereference(p)->d_inode;
+	if (pi && !test_bit(NFS_INO_SEEN_GETATTR, &NFS_I(pi)->flags))
+		set_bit(NFS_INO_SEEN_GETATTR, &NFS_I(pi)->flags);
+	rcu_read_unlock();
 
 	/* Flush out writes to the server in order to update c/mtime.  */
 	if (S_ISREG(inode->i_mode)) {
--- linux-2.6.37-openSUSE-11.4.orig/include/linux/nfs_fs.h
+++ linux-2.6.37-openSUSE-11.4/include/linux/nfs_fs.h
@@ -220,6 +220,10 @@ struct nfs_inode {
 #define NFS_INO_PNFS_COMMIT	(8)		/* use pnfs code for commit */
 #define NFS_INO_LAYOUTCOMMIT	(9)		/* layoutcommit required */
 #define NFS_INO_LAYOUTCOMMITTING (10)		/* layoutcommit inflight */
+#define NFS_INO_SEEN_GETATTR	(11)		/* flag to track if app is calling
+						 * getattr in a directory during
+						 * readdir
+						 */
 
 static inline struct nfs_inode *NFS_I(const struct inode *inode)
 {