Re: [PATCH RFC 7/9] NFSD: Use rhashtable for managing nfs4_file objects

[Chuck Lever III <chuck.lever@oracle.com>]

> On Oct 5, 2022, at 10:56 AM, Chuck Lever <chuck.lever@oracle.com> wrote:
> 
> fh_match() is expensive to use for hash chains that contain more
> than a few objects. With common workloads, I see multiple thousands
> of objects stored in file_hashtbl[], which always has only 256
> buckets.
> 
> Replace it with an rhashtable, which dynamically resizes its bucket
> array to keep hash chains short.
> 
> This also enables the removal of the use of state_lock to serialize
> operations on the new rhashtable.
> 
> The result is an improvement in the latency of NFSv4 operations
> and the reduction of nfsd CPU utilization due to the cache misses
> of walking long hash chains in file_hashtbl.
> 
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> Reviewed-by: Jeff Layton <jlayton@kernel.org>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
> fs/nfsd/nfs4state.c |  229 +++++++++++++++++++++++++++++++++++----------------
> fs/nfsd/state.h     |    5 -
> 2 files changed, 158 insertions(+), 76 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 2b850de288cf..06499b9481a6 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"
> @@ -84,6 +86,7 @@ static bool check_for_locks(struct nfs4_file *fp, struct nfs4_lockowner *lowner)
> static void nfs4_free_ol_stateid(struct nfs4_stid *stid);
> void nfsd4_end_grace(struct nfsd_net *nn);
> static void _free_cpntf_state_locked(struct nfsd_net *nn, struct nfs4_cpntf_state *cps);
> +static void unhash_nfs4_file(struct nfs4_file *fp);
> 
> /* Locking: */
> 
> @@ -577,11 +580,8 @@ 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)) {
> -		hlist_del_rcu(&fi->fi_hash);
> -		spin_unlock(&state_lock);
> +	if (refcount_dec_and_test(&fi->fi_ref)) {
> +		unhash_nfs4_file(fi);
> 		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);
> @@ -695,19 +695,85 @@ 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 struct rhashtable nfs4_file_rhashtbl ____cacheline_aligned_in_smp;
> 
> -static unsigned int file_hashval(struct svc_fh *fh)
> +/*
> + * The returned hash value is based solely on the address of an in-code
> + * inode, a pointer to a slab-allocated object. The entropy in such a
> + * pointer is concentrated in its middle bits.
> + */
> +static u32 nfs4_file_inode_hash(const struct inode *inode, u32 seed)
> +{
> +	unsigned long ptr = (unsigned long)inode;
> +	u32 k;
> +
> +	k = ptr >> L1_CACHE_SHIFT;
> +	k &= 0x00ffffff;
> +	return jhash2(&k, 1, seed);
> +}
> +
> +/**
> + * nfs4_file_key_hashfn - Compute the hash value of a lookup key
> + * @data: key on which to compute the hash value
> + * @len: rhash table's key_len parameter (unused)
> + * @seed: rhash table's random seed of the day
> + *
> + * Return value:
> + *   Computed 32-bit hash value
> + */
> +static u32 nfs4_file_key_hashfn(const void *data, u32 len, u32 seed)
> {
> -	struct inode *inode = d_inode(fh->fh_dentry);
> +	const struct svc_fh *fhp = data;
> 
> -	/* XXX: why not (here & in file cache) use inode? */
> -	return (unsigned int)hash_long(inode->i_ino, FILE_HASH_BITS);
> +	return nfs4_file_inode_hash(d_inode(fhp->fh_dentry), seed);
> }
> 
> -static struct hlist_head file_hashtbl[FILE_HASH_SIZE];
> +/**
> + * nfs4_file_obj_hashfn - Compute the hash value of an nfs4_file object
> + * @data: object on which to compute the hash value
> + * @len: rhash table's key_len parameter (unused)
> + * @seed: rhash table's random seed of the day
> + *
> + * Return value:
> + *   Computed 32-bit hash value
> + */
> +static u32 nfs4_file_obj_hashfn(const void *data, u32 len, u32 seed)
> +{
> +	const struct nfs4_file *fi = data;
> +
> +	return nfs4_file_inode_hash(fi->fi_inode, seed);
> +}
> +
> +/**
> + * nfs4_file_obj_cmpfn - Match a cache item against search criteria
> + * @arg: search criteria
> + * @ptr: cache item to check
> + *
> + * Return values:
> + *   %0 - Item matches search criteria
> + *   %1 - Item does not match search criteria
> + */
> +static int nfs4_file_obj_cmpfn(struct rhashtable_compare_arg *arg,
> +			       const void *ptr)
> +{
> +	const struct svc_fh *fhp = arg->key;
> +	const struct nfs4_file *fi = ptr;
> +
> +	return fh_match(&fi->fi_fhandle, &fhp->fh_handle) ? 0 : 1;
> +}
> +
> +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_rhash),
> +	.hashfn			= nfs4_file_key_hashfn,
> +	.obj_hashfn		= nfs4_file_obj_hashfn,
> +	.obj_cmpfn		= nfs4_file_obj_cmpfn,
> +
> +	/* Reduce resizing churn on light workloads */
> +	.min_size		= 512,		/* buckets */
> +	.automatic_shrinking	= true,
> +};
> 
> /*
>  * Check if courtesy clients have conflicting access and resolve it if possible
> @@ -4251,11 +4317,8 @@ static struct nfs4_file *nfsd4_alloc_file(void)
> }
> 
> /* OPEN Share state helper functions */
> -static void nfsd4_init_file(struct svc_fh *fh, unsigned int hashval,
> -				struct nfs4_file *fp)
> +static void init_nfs4_file(const struct svc_fh *fh, struct nfs4_file *fp)
> {
> -	lockdep_assert_held(&state_lock);
> -
> 	refcount_set(&fp->fi_ref, 1);
> 	spin_lock_init(&fp->fi_lock);
> 	INIT_LIST_HEAD(&fp->fi_stateids);
> @@ -4273,7 +4336,6 @@ static void nfsd4_init_file(struct svc_fh *fh, unsigned int hashval,
> 	INIT_LIST_HEAD(&fp->fi_lo_states);
> 	atomic_set(&fp->fi_lo_recalls, 0);
> #endif
> -	hlist_add_head_rcu(&fp->fi_hash, &file_hashtbl[hashval]);
> }
> 
> void
> @@ -4626,71 +4688,84 @@ move_to_close_lru(struct nfs4_ol_stateid *s, struct net *net)
> 		nfs4_put_stid(&last->st_stid);
> }
> 
> -/* search file_hashtbl[] for file */
> -static struct nfs4_file *
> -find_file_locked(struct svc_fh *fh, unsigned int hashval)
> +static struct nfs4_file *find_nfs4_file(const struct svc_fh *fhp)
> {
> -	struct nfs4_file *fp;
> +	struct nfs4_file *fi;
> 
> -	hlist_for_each_entry_rcu(fp, &file_hashtbl[hashval], fi_hash,
> -				lockdep_is_held(&state_lock)) {
> -		if (fh_match(&fp->fi_fhandle, &fh->fh_handle)) {
> -			if (refcount_inc_not_zero(&fp->fi_ref))
> -				return fp;
> -		}
> -	}
> -	return NULL;
> +	rcu_read_lock();
> +	fi = rhashtable_lookup(&nfs4_file_rhashtbl, fhp,
> +			       nfs4_file_rhash_params);
> +	if (fi)
> +		if (!refcount_inc_not_zero(&fi->fi_ref))
> +			fi = NULL;
> +	rcu_read_unlock();
> +	return fi;
> }
> 
> -static struct nfs4_file *insert_file(struct nfs4_file *new, struct svc_fh *fh,
> -				     unsigned int hashval)
> +static void check_nfs4_file_aliases_locked(struct nfs4_file *new,
> +					   const struct svc_fh *fhp)
> {
> -	struct nfs4_file *fp;
> -	struct nfs4_file *ret = NULL;
> -	bool alias_found = false;
> +	struct rhashtable *ht = &nfs4_file_rhashtbl;
> +	struct rhash_lock_head __rcu *const *bkt;
> +	struct rhashtable_compare_arg arg = {
> +		.ht	= ht,
> +		.key	= fhp,
> +	};
> +	struct bucket_table *tbl;
> +	struct rhash_head *he;
> +	unsigned int hash;
> 
> -	spin_lock(&state_lock);
> -	hlist_for_each_entry_rcu(fp, &file_hashtbl[hashval], fi_hash,
> -				 lockdep_is_held(&state_lock)) {
> -		if (fh_match(&fp->fi_fhandle, &fh->fh_handle)) {
> -			if (refcount_inc_not_zero(&fp->fi_ref))
> -				ret = fp;
> -		} else if (d_inode(fh->fh_dentry) == fp->fi_inode)
> -			fp->fi_aliased = alias_found = true;
> -	}
> -	if (likely(ret == NULL)) {
> -		nfsd4_init_file(fh, hashval, new);
> -		new->fi_aliased = alias_found;
> -		ret = new;
> +	/*
> +	 * rhashtable guarantees small buckets, thus this loop stays
> +	 * efficient.
> +	 */
> +	rcu_read_lock();
> +	tbl = rht_dereference_rcu(ht->tbl, ht);
> +	hash = rht_key_hashfn(ht, tbl, fhp, nfs4_file_rhash_params);
> +	bkt = rht_bucket(tbl, hash);
> +	rht_for_each_rcu_from(he, rht_ptr_rcu(bkt), tbl, hash) {
> +		struct nfs4_file *fi;
> +
> +		fi = rht_obj(ht, he);
> +		if (nfs4_file_obj_cmpfn(&arg, fi) == 0)
> +			continue;
> +		if (d_inode(fhp->fh_dentry) == fi->fi_inode) {
> +			fi->fi_aliased = true;
> +			new->fi_aliased = true;
> +		}
> 	}
> -	spin_unlock(&state_lock);
> -	return ret;
> +	rcu_read_unlock();
> }
> 
> -static struct nfs4_file * find_file(struct svc_fh *fh)
> +static noinline struct nfs4_file *
> +find_or_hash_nfs4_file(struct nfs4_file *new, const struct svc_fh *fhp)
> {
> -	struct nfs4_file *fp;
> -	unsigned int hashval = file_hashval(fh);
> +	struct nfs4_file *fi;
> 
> -	rcu_read_lock();
> -	fp = find_file_locked(fh, hashval);
> -	rcu_read_unlock();
> -	return fp;
> -}
> +	init_nfs4_file(fhp, new);
> 
> -static struct nfs4_file *
> -find_or_add_file(struct nfs4_file *new, struct svc_fh *fh)
> -{
> -	struct nfs4_file *fp;
> -	unsigned int hashval = file_hashval(fh);
> +	fi = rhashtable_lookup_get_insert_key(&nfs4_file_rhashtbl,
> +					      fhp, &new->fi_rhash,
> +					      nfs4_file_rhash_params);
> +	if (!fi) {
> +		fi = new;
> +		goto check_aliases;
> +	}
> +	if (IS_ERR(fi))		/* or BUG? */
> +		return NULL;
> +	if (!refcount_inc_not_zero(&fi->fi_ref))
> +		fi = new;

Ah, hrm. Given what we just had to do to nfsd_file_do_acquire(),
maybe this needs the same fix to hang onto the RCU read lock
while dicking with the nfs4_file object's reference count?


> -	rcu_read_lock();
> -	fp = find_file_locked(fh, hashval);
> -	rcu_read_unlock();
> -	if (fp)
> -		return fp;
> +check_aliases:
> +	check_nfs4_file_aliases_locked(fi, fhp);
> +
> +	return fi;
> +}
> 
> -	return insert_file(new, fh, hashval);
> +static void unhash_nfs4_file(struct nfs4_file *fi)
> +{
> +	rhashtable_remove_fast(&nfs4_file_rhashtbl, &fi->fi_rhash,
> +			       nfs4_file_rhash_params);
> }
> 
> /*
> @@ -4703,9 +4778,10 @@ nfs4_share_conflict(struct svc_fh *current_fh, unsigned int deny_type)
> 	struct nfs4_file *fp;
> 	__be32 ret = nfs_ok;
> 
> -	fp = find_file(current_fh);
> +	fp = find_nfs4_file(current_fh);
> 	if (!fp)
> 		return ret;
> +
> 	/* Check for conflicting share reservations */
> 	spin_lock(&fp->fi_lock);
> 	if (fp->fi_share_deny & deny_type)
> @@ -5548,7 +5624,9 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
> 	 * and check for delegations in the process of being recalled.
> 	 * If not found, create the nfs4_file struct
> 	 */
> -	fp = find_or_add_file(open->op_file, current_fh);
> +	fp = find_or_hash_nfs4_file(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)
> @@ -7905,10 +7983,16 @@ nfs4_state_start(void)
> {
> 	int ret;
> 
> -	ret = nfsd4_create_callback_queue();
> +	ret = rhashtable_init(&nfs4_file_rhashtbl, &nfs4_file_rhash_params);
> 	if (ret)
> 		return ret;
> 
> +	ret = nfsd4_create_callback_queue();
> +	if (ret) {
> +		rhashtable_destroy(&nfs4_file_rhashtbl);
> +		return ret;
> +	}
> +
> 	set_max_delegations();
> 	return 0;
> }
> @@ -7939,6 +8023,7 @@ nfs4_state_shutdown_net(struct net *net)
> 
> 	nfsd4_client_tracking_exit(net);
> 	nfs4_state_destroy_net(net);
> +	rhashtable_destroy(&nfs4_file_rhashtbl);
> #ifdef CONFIG_NFSD_V4_2_INTER_SSC
> 	nfsd4_ssc_shutdown_umount(nn);
> #endif
> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
> index ae596dbf8667..879f085bc39e 100644
> --- a/fs/nfsd/state.h
> +++ b/fs/nfsd/state.h
> @@ -536,16 +536,13 @@ struct nfs4_clnt_odstate {
>  * inode can have multiple filehandles associated with it, so there is
>  * (potentially) a many to one relationship between this struct and struct
>  * inode.
> - *
> - * These are hashed by filehandle in the file_hashtbl, which is protected by
> - * the global state_lock spinlock.
>  */
> struct nfs4_file {
> 	refcount_t		fi_ref;
> 	struct inode *		fi_inode;
> 	bool			fi_aliased;
> 	spinlock_t		fi_lock;
> -	struct hlist_node       fi_hash;	/* hash on fi_fhandle */
> +	struct rhash_head	fi_rhash;
> 	struct list_head        fi_stateids;
> 	union {
> 		struct list_head	fi_delegations;
> 
> 

--
Chuck Lever