[PATCH 24/24] NFS: make nfs_mark_return_unreferenced_delegations less aggressive

[Christoph Hellwig <hch@lst.de>]

Currently nfs_mark_return_unreferenced_delegations marks all open but
not referenced delegations (i.e., those were found by a previous pass)
as return on close, which means that we'll return them on close without
a way out.

Replace this with only iterating delegations that are on the LRU list,
and avoid delegations that are in use by an open files to avoid this.

Delegations that were never referenced while open still are be prime
candidates for return from the LRU if the number of delegations is over
the watermark, or otherwise will be returned by the next
nfs_mark_return_unreferenced_delegations pass after they are closed.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/nfs/delegation.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index 712cdb3381ad..776020bdf8f3 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -1126,15 +1126,21 @@ void nfs_remove_bad_delegation(struct inode *inode,
 }
 EXPORT_SYMBOL_GPL(nfs_remove_bad_delegation);
 
-static void nfs_mark_return_unreferenced_delegations(struct nfs_server *server)
+static bool nfs_mark_return_unreferenced_delegations(struct nfs_server *server)
 {
-	struct nfs_delegation *delegation;
+	struct nfs_delegation *d, *n;
+	bool marked = false;
 
-	list_for_each_entry_rcu(delegation, &server->delegations, super_list) {
-		if (test_and_clear_bit(NFS_DELEGATION_REFERENCED, &delegation->flags))
+	spin_lock(&server->delegations_lock);
+	list_for_each_entry_safe(d, n, &server->delegations_lru, entry) {
+		if (test_and_clear_bit(NFS_DELEGATION_REFERENCED, &d->flags))
 			continue;
-		nfs_mark_return_if_closed_delegation(server, delegation);
+		list_move_tail(&d->entry, &server->delegations_return);
+		marked = true;
 	}
+	spin_unlock(&server->delegations_lock);
+
+	return marked;
 }
 
 /**
@@ -1145,13 +1151,17 @@ static void nfs_mark_return_unreferenced_delegations(struct nfs_server *server)
 void nfs_expire_unreferenced_delegations(struct nfs_client *clp)
 {
 	struct nfs_server *server;
+	bool marked = false;
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(server, &clp->cl_superblocks, client_link)
-		nfs_mark_return_unreferenced_delegations(server);
+		marked |= nfs_mark_return_unreferenced_delegations(server);
 	rcu_read_unlock();
 
-	nfs_delegation_run_state_manager(clp);
+	if (marked) {
+		set_bit(NFS4CLNT_DELEGRETURN, &clp->cl_state);
+		nfs4_schedule_state_manager(clp);
+	}
 }
 
 /**
-- 
2.47.3