[PATCH] NFS: Fix directory delegation verifier checks

[Anna Schumaker <anna@kernel.org>]

From: Anna Schumaker <anna.schumaker@oracle.com>

Doing this check in nfs_check_verifier() resulted in many, many more
lookups on the wire when running Christoph's delegation benchmarking
script. After some experimentation, I found that we can treat directory
delegations exactly the same as having a delegated verifier when we
reach nfs4_lookup_revalidate() for the best performance.

Reported-by: Christoph Hellwig <hch@lst.de>
Fixes: 156b09482933 ("NFS: Request a directory delegation on ACCESS, CREATE, and UNLINK")
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
---
 fs/nfs/dir.c | 21 ++-------------------
 1 file changed, 2 insertions(+), 19 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 23a78a742b61..c0e9d5a45cd0 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1516,14 +1516,6 @@ static int nfs_check_verifier(struct inode *dir, struct dentry *dentry,
 	if (!nfs_dentry_verify_change(dir, dentry))
 		return 0;
 
-	/*
-	 * If we have a directory delegation then we don't need to revalidate
-	 * the directory. The delegation will either get recalled or we will
-	 * receive a notification when it changes.
-	 */
-	if (nfs_have_directory_delegation(dir))
-		return 0;
-
 	/* Revalidate nfsi->cache_change_attribute before we declare a match */
 	if (nfs_mapping_need_revalidate_inode(dir)) {
 		if (rcu_walk)
@@ -2216,13 +2208,6 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
 }
 EXPORT_SYMBOL_GPL(nfs_atomic_open);
 
-static int
-nfs_lookup_revalidate_delegated_parent(struct inode *dir, struct dentry *dentry,
-				       struct inode *inode)
-{
-	return nfs_lookup_revalidate_done(dir, dentry, inode, 1);
-}
-
 static int
 nfs4_lookup_revalidate(struct inode *dir, const struct qstr *name,
 		       struct dentry *dentry, unsigned int flags)
@@ -2247,12 +2232,10 @@ nfs4_lookup_revalidate(struct inode *dir, const struct qstr *name,
 	if (inode == NULL)
 		goto full_reval;
 
-	if (nfs_verifier_is_delegated(dentry))
+	if (nfs_verifier_is_delegated(dentry) ||
+	    nfs_have_directory_delegation(inode))
 		return nfs_lookup_revalidate_delegated(dir, dentry, inode);
 
-	if (nfs_have_directory_delegation(dir))
-		return nfs_lookup_revalidate_delegated_parent(dir, dentry, inode);
-
 	/* NFS only supports OPEN on regular files */
 	if (!S_ISREG(inode->i_mode))
 		goto full_reval;
-- 
2.52.0