NFSD: Use rhashtable for managing nfs4_file objects

fh_match() is costly, especially when filehandles are large (as is
the case for NFSv4). It needs to be used sparingly when searching
data structures. Unfortunately, with common workloads, I see
multiple thousands of objects stored in file_hashtbl[], which has
just 256 buckets, making its bucket hash chains quite lengthy.

Walking long hash chains with the state_lock held blocks other
activity that needs that lock. Sizable hash chains are a common
occurrance once the server has handed out some delegations, for
example -- IIUC, each delegated file is held open on the server by
an nfs4_file object.

To help mitigate the cost of searching with fh_match(), replace the
nfs4_file hash table with an rhashtable, which can dynamically
resize its bucket array to minimize hash chain length.

The result of this modification is an improvement in the latency of
NFSv4 operations, and the reduction of nfsd CPU utilization due to
eliminating the cost of multiple calls to fh_match() and reducing
the CPU cache misses incurred while walking long hash chains in the
nfs4_file hash table.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>

1 files changed, 62 insertions, 35 deletions

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index a611e7b0f013..2ec981fd2985 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -44,7 +44,9 @@
 #include <linux/jhash.h>
 #include <linux/string_helpers.h>
 #include <linux/fsnotify.h>
+#include <linux/rhashtable.h>
 #include <linux/nfs_ssc.h>
+
 #include "xdr4.h"
 #include "xdr4cb.h"
 #include "vfs.h"
@@ -589,11 +591,8 @@ static void nfsd4_free_file_rcu(struct rcu_head *rcu)
 void
 put_nfs4_file(struct nfs4_file *fi)
 {
-	might_lock(&state_lock);
-
-	if (refcount_dec_and_lock(&fi->fi_ref, &state_lock)) {
+	if (refcount_dec_and_test(&fi->fi_ref)) {
 		nfsd4_file_hash_remove(fi);
-		spin_unlock(&state_lock);
 		WARN_ON_ONCE(!list_empty(&fi->fi_clnt_odstate));
 		WARN_ON_ONCE(!list_empty(&fi->fi_delegations));
 		call_rcu(&fi->fi_rcu, nfsd4_free_file_rcu);
@@ -718,19 +717,20 @@ static unsigned int ownerstr_hashval(struct xdr_netobj *ownername)
 	return ret & OWNER_HASH_MASK;
 }
 
-/* hash table for nfs4_file */
-#define FILE_HASH_BITS                   8
-#define FILE_HASH_SIZE                  (1 << FILE_HASH_BITS)
-
-static unsigned int file_hashval(const struct svc_fh *fh)
-{
-	struct inode *inode = d_inode(fh->fh_dentry);
+static struct rhltable nfs4_file_rhltable ____cacheline_aligned_in_smp;
 
-	/* XXX: why not (here & in file cache) use inode? */
-	return (unsigned int)hash_long(inode->i_ino, FILE_HASH_BITS);
-}
+static const struct rhashtable_params nfs4_file_rhash_params = {
+	.key_len		= sizeof_field(struct nfs4_file, fi_inode),
+	.key_offset		= offsetof(struct nfs4_file, fi_inode),
+	.head_offset		= offsetof(struct nfs4_file, fi_rlist),
 
-static struct hlist_head file_hashtbl[FILE_HASH_SIZE];
+	/*
+	 * Start with a single page hash table to reduce resizing churn
+	 * on light workloads.
+	 */
+	.min_size		= 256,
+	.automatic_shrinking	= true,
+};
 
 /*
  * Check if courtesy clients have conflicting access and resolve it if possible
@@ -4685,12 +4685,14 @@ move_to_close_lru(struct nfs4_ol_stateid *s, struct net *net)
 static noinline_for_stack struct nfs4_file *
 nfsd4_file_hash_lookup(const struct svc_fh *fhp)
 {
-	unsigned int hashval = file_hashval(fhp);
+	struct inode *inode = d_inode(fhp->fh_dentry);
+	struct rhlist_head *tmp, *list;
 	struct nfs4_file *fi;
 
 	rcu_read_lock();
-	hlist_for_each_entry_rcu(fi, &file_hashtbl[hashval], fi_hash,
-				 lockdep_is_held(&state_lock)) {
+	list = rhltable_lookup(&nfs4_file_rhltable, &inode,
+			       nfs4_file_rhash_params);
+	rhl_for_each_entry_rcu(fi, tmp, list, fi_rlist) {
 		if (fh_match(&fi->fi_fhandle, &fhp->fh_handle)) {
 			if (refcount_inc_not_zero(&fi->fi_ref)) {
 				rcu_read_unlock();
@@ -4704,40 +4706,56 @@ nfsd4_file_hash_lookup(const struct svc_fh *fhp)
 
 /*
  * On hash insertion, identify entries with the same inode but
- * distinct filehandles. They will all be in the same hash bucket
- * because nfs4_file's are hashed by the address in the fi_inode
- * field.
+ * distinct filehandles. They will all be on the list returned
+ * by rhltable_lookup().
+ *
+ * inode->i_lock prevents racing insertions from adding an entry
+ * for the same inode/fhp pair twice.
  */
 static noinline_for_stack struct nfs4_file *
 nfsd4_file_hash_insert(struct nfs4_file *new, const struct svc_fh *fhp)
 {
-	unsigned int hashval = file_hashval(fhp);
+	struct inode *inode = d_inode(fhp->fh_dentry);
+	struct rhlist_head *tmp, *list;
 	struct nfs4_file *ret = NULL;
 	bool alias_found = false;
 	struct nfs4_file *fi;
+	int err;
 
-	spin_lock(&state_lock);
-	hlist_for_each_entry_rcu(fi, &file_hashtbl[hashval], fi_hash,
-				 lockdep_is_held(&state_lock)) {
+	rcu_read_lock();
+	spin_lock(&inode->i_lock);
+
+	list = rhltable_lookup(&nfs4_file_rhltable, &inode,
+			       nfs4_file_rhash_params);
+	rhl_for_each_entry_rcu(fi, tmp, list, fi_rlist) {
 		if (fh_match(&fi->fi_fhandle, &fhp->fh_handle)) {
 			if (refcount_inc_not_zero(&fi->fi_ref))
 				ret = fi;
-		} else if (d_inode(fhp->fh_dentry) == fi->fi_inode)
+		} else
 			fi->fi_aliased = alias_found = true;
 	}
-	if (likely(ret == NULL)) {
-		nfsd4_file_init(fhp, new);
-		hlist_add_head_rcu(&new->fi_hash, &file_hashtbl[hashval]);
-		new->fi_aliased = alias_found;
-		ret = new;
-	}
-	spin_unlock(&state_lock);
+	if (ret)
+		goto out_unlock;
+
+	nfsd4_file_init(fhp, new);
+	err = rhltable_insert(&nfs4_file_rhltable, &new->fi_rlist,
+			      nfs4_file_rhash_params);
+	if (err)
+		goto out_unlock;
+
+	new->fi_aliased = alias_found;
+	ret = new;
+
+out_unlock:
+	spin_unlock(&inode->i_lock);
+	rcu_read_unlock();
 	return ret;
 }
 
 static noinline_for_stack void nfsd4_file_hash_remove(struct nfs4_file *fi)
 {
-	hlist_del_rcu(&fi->fi_hash);
+	rhltable_remove(&nfs4_file_rhltable, &fi->fi_rlist,
+			nfs4_file_rhash_params);
 }
 
 /*
@@ -5628,6 +5646,8 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
 	 * If not found, create the nfs4_file struct
 	 */
 	fp = nfsd4_file_hash_insert(open->op_file, current_fh);
+	if (unlikely(!fp))
+		return nfserr_jukebox;
 	if (fp != open->op_file) {
 		status = nfs4_check_deleg(cl, open, &dp);
 		if (status)
@@ -8042,10 +8062,16 @@ nfs4_state_start(void)
 {
 	int ret;
 
-	ret = nfsd4_create_callback_queue();
+	ret = rhltable_init(&nfs4_file_rhltable, &nfs4_file_rhash_params);
 	if (ret)
 		return ret;
 
+	ret = nfsd4_create_callback_queue();
+	if (ret) {
+		rhltable_destroy(&nfs4_file_rhltable);
+		return ret;
+	}
+
 	set_max_delegations();
 	return 0;
 }
@@ -8076,6 +8102,7 @@ nfs4_state_shutdown_net(struct net *net)
 
 	nfsd4_client_tracking_exit(net);
 	nfs4_state_destroy_net(net);
+	rhltable_destroy(&nfs4_file_rhltable);
 #ifdef CONFIG_NFSD_V4_2_INTER_SSC
 	nfsd4_ssc_shutdown_umount(nn);
 #endif