NFSv4: Avoid thundering herd issues with nfs_release_seqid

Store a pointer to the rpc_task in struct nfs_seqid so that we can wake up
only that request that is able to grab the lock after we've released it.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h
index c45c21a..b133b50 100644 (file)
--- a/fs/nfs/nfs4_fs.h
+++ b/fs/nfs/nfs4_fs.h
@@ -71,6 +71,7 @@ struct nfs_seqid_counter {
 struct nfs_seqid {
        struct nfs_seqid_counter *sequence;
        struct list_head list;
+       struct rpc_task *task;
 };
 
 static inline void nfs_confirm_seqid(struct nfs_seqid_counter *seqid, int status)

diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index f0e9881..7d09860 100644 (file)
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -916,20 +916,28 @@ struct nfs_seqid *nfs_alloc_seqid(struct nfs_seqid_counter *counter, gfp_t gfp_m
        if (new != NULL) {
                new->sequence = counter;
                INIT_LIST_HEAD(&new->list);
+               new->task = NULL;
        }
        return new;
 }
 
 void nfs_release_seqid(struct nfs_seqid *seqid)
 {
-       if (!list_empty(&seqid->list)) {
-               struct nfs_seqid_counter *sequence = seqid->sequence;
+       struct nfs_seqid_counter *sequence;
 
-               spin_lock(&sequence->lock);
-               list_del_init(&seqid->list);
-               spin_unlock(&sequence->lock);
-               rpc_wake_up(&sequence->wait);
+       if (list_empty(&seqid->list))
+               return;
+       sequence = seqid->sequence;
+       spin_lock(&sequence->lock);
+       list_del_init(&seqid->list);
+       if (!list_empty(&sequence->list)) {
+               struct nfs_seqid *next;
+
+               next = list_first_entry(&sequence->list,
+                               struct nfs_seqid, list);
+               rpc_wake_up_queued_task(&sequence->wait, next->task);
        }
+       spin_unlock(&sequence->lock);
 }
 
 void nfs_free_seqid(struct nfs_seqid *seqid)
@@ -1000,6 +1008,7 @@ int nfs_wait_on_sequence(struct nfs_seqid *seqid, struct rpc_task *task)
        int status = 0;
 
        spin_lock(&sequence->lock);
+       seqid->task = task;
        if (list_empty(&seqid->list))
                list_add_tail(&seqid->list, &sequence->list);
        if (list_first_entry(&sequence->list, struct nfs_seqid, list) == seqid)