On Wed, 2022-10-05 at 15:11 +0000, Chuck Lever III wrote:
>
> > On Oct 5, 2022, at 10:56 AM, Chuck Lever <chuck.lever@xxxxxxxxxx> 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@xxxxxxxxxx>
> > Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> > ---
> > 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?
>
>
Yes. Probably we should just merge this patch if you want a fix for
mainline:
nfsd: rework hashtable handling in nfsd_do_file_acquire
> > - 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
>
>
>
--
Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
