On Thu, Oct 23, 2014 at 08:01:02AM -0400, Jeff Layton wrote:
> The global state_lock protects the file_hashtbl, and that has the
> potential to be a scalability bottleneck.
>
> Address this by making the file_hashtbl use RCU. Add a rcu_head to the
> nfs4_file and use that when freeing ones that have been hashed. In order
> to conserve space, we union the fi_rcu field with the fi_delegations
> list_head which must be clear by the time the last reference to the file
> is dropped.
>
> Convert find_file_locked to use RCU lookup primitives and not to require
> that the state_lock be held, and convert find_file to do a lockless
> lookup. Convert find_or_add_file to attempt a lockless lookup first, and
> then fall back to doing a locked search and insert if that fails to find
> anything.
>
> Also, minimize the number of times we need to calculate the hash value
> by passing it in as an argument to the search and insert functions, and
> optimize the order of arguments in nfsd4_init_file.
OK, looks fine, thanks. Applying for 3.19.
In general though I'd like to see more evidence when we're making
changes for performance reasons.
--b.
>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
> ---
> fs/nfsd/nfs4state.c | 51 +++++++++++++++++++++++++++++----------------------
> fs/nfsd/state.h | 5 ++++-
> 2 files changed, 33 insertions(+), 23 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 1afd7d4420bd..1379d86f7b4f 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -275,9 +275,11 @@ opaque_hashval(const void *ptr, int nbytes)
> return x;
> }
>
> -static void nfsd4_free_file(struct nfs4_file *f)
> +static void nfsd4_free_file_rcu(struct rcu_head *rcu)
> {
> - kmem_cache_free(file_slab, f);
> + struct nfs4_file *fp = container_of(rcu, struct nfs4_file, fi_rcu);
> +
> + kmem_cache_free(file_slab, fp);
> }
>
> static inline void
> @@ -286,9 +288,10 @@ put_nfs4_file(struct nfs4_file *fi)
> might_lock(&state_lock);
>
> if (atomic_dec_and_lock(&fi->fi_ref, &state_lock)) {
> - hlist_del(&fi->fi_hash);
> + hlist_del_rcu(&fi->fi_hash);
> spin_unlock(&state_lock);
> - nfsd4_free_file(fi);
> + WARN_ON_ONCE(!list_empty(&fi->fi_delegations));
> + call_rcu(&fi->fi_rcu, nfsd4_free_file_rcu);
> }
> }
>
> @@ -3057,10 +3060,9 @@ static struct nfs4_file *nfsd4_alloc_file(void)
> }
>
> /* OPEN Share state helper functions */
> -static void nfsd4_init_file(struct nfs4_file *fp, struct knfsd_fh *fh)
> +static void nfsd4_init_file(struct knfsd_fh *fh, unsigned int hashval,
> + struct nfs4_file *fp)
> {
> - unsigned int hashval = file_hashval(fh);
> -
> lockdep_assert_held(&state_lock);
>
> atomic_set(&fp->fi_ref, 1);
> @@ -3073,7 +3075,7 @@ static void nfsd4_init_file(struct nfs4_file *fp, struct knfsd_fh *fh)
> fp->fi_share_deny = 0;
> memset(fp->fi_fds, 0, sizeof(fp->fi_fds));
> memset(fp->fi_access, 0, sizeof(fp->fi_access));
> - hlist_add_head(&fp->fi_hash, &file_hashtbl[hashval]);
> + hlist_add_head_rcu(&fp->fi_hash, &file_hashtbl[hashval]);
> }
>
> void
> @@ -3294,17 +3296,14 @@ move_to_close_lru(struct nfs4_ol_stateid *s, struct net *net)
>
> /* search file_hashtbl[] for file */
> static struct nfs4_file *
> -find_file_locked(struct knfsd_fh *fh)
> +find_file_locked(struct knfsd_fh *fh, unsigned int hashval)
> {
> - unsigned int hashval = file_hashval(fh);
> struct nfs4_file *fp;
>
> - lockdep_assert_held(&state_lock);
> -
> - hlist_for_each_entry(fp, &file_hashtbl[hashval], fi_hash) {
> + hlist_for_each_entry_rcu(fp, &file_hashtbl[hashval], fi_hash) {
> if (nfsd_fh_match(&fp->fi_fhandle, fh)) {
> - get_nfs4_file(fp);
> - return fp;
> + if (atomic_inc_not_zero(&fp->fi_ref))
> + return fp;
> }
> }
> return NULL;
> @@ -3314,10 +3313,11 @@ static struct nfs4_file *
> find_file(struct knfsd_fh *fh)
> {
> struct nfs4_file *fp;
> + unsigned int hashval = file_hashval(fh);
>
> - spin_lock(&state_lock);
> - fp = find_file_locked(fh);
> - spin_unlock(&state_lock);
> + rcu_read_lock();
> + fp = find_file_locked(fh, hashval);
> + rcu_read_unlock();
> return fp;
> }
>
> @@ -3325,11 +3325,18 @@ static struct nfs4_file *
> find_or_add_file(struct nfs4_file *new, struct knfsd_fh *fh)
> {
> struct nfs4_file *fp;
> + unsigned int hashval = file_hashval(fh);
> +
> + rcu_read_lock();
> + fp = find_file_locked(fh, hashval);
> + rcu_read_unlock();
> + if (fp)
> + return fp;
>
> spin_lock(&state_lock);
> - fp = find_file_locked(fh);
> - if (fp == NULL) {
> - nfsd4_init_file(new, fh);
> + fp = find_file_locked(fh, hashval);
> + if (likely(fp == NULL)) {
> + nfsd4_init_file(fh, hashval, new);
> fp = new;
> }
> spin_unlock(&state_lock);
> @@ -4127,7 +4134,7 @@ void nfsd4_cleanup_open_state(struct nfsd4_compound_state *cstate,
> nfs4_put_stateowner(so);
> }
> if (open->op_file)
> - nfsd4_free_file(open->op_file);
> + kmem_cache_free(file_slab, open->op_file);
> if (open->op_stp)
> nfs4_put_stid(&open->op_stp->st_stid);
> }
> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
> index 8e85e07efce6..9d3be371240a 100644
> --- a/fs/nfsd/state.h
> +++ b/fs/nfsd/state.h
> @@ -477,7 +477,10 @@ struct nfs4_file {
> spinlock_t fi_lock;
> struct hlist_node fi_hash; /* hash on fi_fhandle */
> struct list_head fi_stateids;
> - struct list_head fi_delegations;
> + union {
> + struct list_head fi_delegations;
> + struct rcu_head fi_rcu;
> + };
> /* One each for O_RDONLY, O_WRONLY, O_RDWR: */
> struct file * fi_fds[3];
> /*
> --
> 1.9.3
>
--
To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
