[PATCH 19/21] NFSv4/pnfs: Re-home the data-server cache onto hash buckets

Mechanical conversion of the per-net data-server cache from a single
list_head to an array of hlist buckets: nfs4_pnfs_ds.ds_node becomes
an hlist_node, netns init/teardown cover every bucket, and removal
uses hlist_del_init (which needs no bucket reference).

Insertion still targets bucket 0 and lookup still scans every entry,
so behavior and cost are unchanged -- keying the buckets by the DS
address set comes next.  Splitting the structural churn from the
keying keeps a bisect able to tell a list-conversion bug from a
hash-key bug.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Benjamin Coddington <[email protected]>
---
 fs/nfs/client.c   |  6 ++++--
 fs/nfs/netns.h    |  5 ++++-
 fs/nfs/pnfs.h     |  2 +-
 fs/nfs/pnfs_nfs.c | 17 ++++++++++-------
 4 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 4dcb91ab3039..10eeb14d251b 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -1283,7 +1283,8 @@ void nfs_clients_init(struct net *net)
 	INIT_LIST_HEAD(&nn->nfs_volume_list);
 #if IS_ENABLED(CONFIG_NFS_V4)
 	idr_init(&nn->cb_ident_idr);
-	INIT_LIST_HEAD(&nn->nfs4_data_server_cache);
+	for (int i = 0; i < NFS4_DS_CACHE_HASH_SIZE; i++)
+		INIT_HLIST_HEAD(&nn->nfs4_data_server_cache[i]);
 	spin_lock_init(&nn->nfs4_data_server_lock);
 #endif /* CONFIG_NFS_V4 */
 	spin_lock_init(&nn->nfs_client_lock);
@@ -1303,7 +1304,8 @@ void nfs_clients_exit(struct net *net)
 	WARN_ON_ONCE(!list_empty(&nn->nfs_client_list));
 	WARN_ON_ONCE(!list_empty(&nn->nfs_volume_list));
 #if IS_ENABLED(CONFIG_NFS_V4)
-	WARN_ON_ONCE(!list_empty(&nn->nfs4_data_server_cache));
+	for (int i = 0; i < NFS4_DS_CACHE_HASH_SIZE; i++)
+		WARN_ON_ONCE(!hlist_empty(&nn->nfs4_data_server_cache[i]));
 #endif /* CONFIG_NFS_V4 */
 }
 
diff --git a/fs/nfs/netns.h b/fs/nfs/netns.h
index 36658579100d..f21118554272 100644
--- a/fs/nfs/netns.h
+++ b/fs/nfs/netns.h
@@ -31,7 +31,10 @@ struct nfs_net {
 	unsigned short nfs_callback_tcpport;
 	unsigned short nfs_callback_tcpport6;
 	int cb_users[NFS4_MAX_MINOR_VERSION + 1];
-	struct list_head nfs4_data_server_cache;
+#define NFS4_DS_CACHE_HASH_BITS 8
+#define NFS4_DS_CACHE_HASH_SIZE (1 << NFS4_DS_CACHE_HASH_BITS)
+	/* hashed by nfs4_ds_addrs_hash() over the DS's address set */
+	struct hlist_head nfs4_data_server_cache[NFS4_DS_CACHE_HASH_SIZE];
 	spinlock_t nfs4_data_server_lock;
 #endif /* CONFIG_NFS_V4 */
 	struct nfs_netns_client *nfs_client;
diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
index 1ce1cbc32f77..e0a7ae5fe8e9 100644
--- a/fs/nfs/pnfs.h
+++ b/fs/nfs/pnfs.h
@@ -57,7 +57,7 @@ struct nfs4_pnfs_ds_addr {
 };
 
 struct nfs4_pnfs_ds {
-	struct list_head	ds_node;  /* nfs4_pnfs_dev_hlist dev_dslist */
+	struct hlist_node	ds_node;  /* nfs_net nfs4_data_server_cache */
 	char			*ds_remotestr;	/* comma sep list of addrs */
 	struct list_head	ds_addrs;
 	const struct net	*ds_net;
diff --git a/fs/nfs/pnfs_nfs.c b/fs/nfs/pnfs_nfs.c
index f40368f839d0..e15e0059c56b 100644
--- a/fs/nfs/pnfs_nfs.c
+++ b/fs/nfs/pnfs_nfs.c
@@ -604,16 +604,19 @@ _same_data_server_addrs_locked(const struct list_head *dsaddrs1,
 }
 
 /*
- * Lookup DS by addresses.  nfs4_ds_cache_lock is held
+ * Lookup DS by addresses.  nfs4_data_server_lock is held
  */
 static struct nfs4_pnfs_ds *
 _data_server_lookup_locked(const struct nfs_net *nn, const struct list_head *dsaddrs)
 {
 	struct nfs4_pnfs_ds *ds;
 
-	list_for_each_entry(ds, &nn->nfs4_data_server_cache, ds_node)
-		if (_same_data_server_addrs_locked(&ds->ds_addrs, dsaddrs))
-			return ds;
+	for (int i = 0; i < NFS4_DS_CACHE_HASH_SIZE; i++)
+		hlist_for_each_entry(ds, &nn->nfs4_data_server_cache[i],
+				     ds_node)
+			if (_same_data_server_addrs_locked(&ds->ds_addrs,
+							   dsaddrs))
+				return ds;
 	return NULL;
 }
 
@@ -659,7 +662,7 @@ void nfs4_pnfs_ds_put(struct nfs4_pnfs_ds *ds)
 	struct nfs_net *nn = net_generic(ds->ds_net, nfs_net_id);
 
 	if (refcount_dec_and_lock(&ds->ds_count, &nn->nfs4_data_server_lock)) {
-		list_del_init(&ds->ds_node);
+		hlist_del_init(&ds->ds_node);
 		spin_unlock(&nn->nfs4_data_server_lock);
 		destroy_ds(ds);
 	}
@@ -745,10 +748,10 @@ nfs4_pnfs_ds_add(const struct net *net, struct list_head *dsaddrs, gfp_t gfp_fla
 		list_splice_init(dsaddrs, &ds->ds_addrs);
 		ds->ds_remotestr = remotestr;
 		refcount_set(&ds->ds_count, 1);
-		INIT_LIST_HEAD(&ds->ds_node);
+		INIT_HLIST_NODE(&ds->ds_node);
 		ds->ds_net = net;
 		ds->ds_clp = NULL;
-		list_add(&ds->ds_node, &nn->nfs4_data_server_cache);
+		hlist_add_head(&ds->ds_node, &nn->nfs4_data_server_cache[0]);
 		dprintk("%s add new data server %s\n", __func__,
 			ds->ds_remotestr);
 	} else {
-- 
2.53.0