On Tue, 2022-10-18 at 15:58 -0400, Chuck Lever wrote:
> fh_match() is costly, especially when filehandles are large (as is
> the case for NFSv4). It needs to be used sparingly when searching
> data structures. Unfortunately, with common workloads, I see
> multiple thousands of objects stored in file_hashtbl[], which always
> has only 256 buckets, which makes the hash chains quite lengthy.
>
> Walking long hash chains with the state_lock held blocks other
> activity that needs that lock.
>
> To help mitigate the cost of searching with fh_match(), replace the
> nfs4_file hash table with an rhashtable, which can dynamically
> resize its bucket array to minimize hash chain length. The ideal for
> this use case is one bucket per inode.
>
> The result is an improvement in the latency of NFSv4 operations
> and the reduction of nfsd CPU utilization due to the cost of
> fh_match() and the CPU cache misses incurred while walking long
> hash chains in the nfs4_file hash table.
>
> Note that hash removal is no longer protected by the state_lock.
> This is because insert_nfs4_file() takes the RCU read lock then the
> state_lock. rhltable_remove() takes the RCU read lock internally;
> if remove_nfs4_file() took the state_lock before calling
> rhltable_remove(), that would result in a lock inversion.
>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> fs/nfsd/nfs4state.c | 215 +++++++++++++++++++++++++++++++++++----------------
> fs/nfsd/state.h | 5 -
> 2 files changed, 147 insertions(+), 73 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 2b850de288cf..a63334ad61f6 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 remove_nfs4_file(struct nfs4_file *fi);
>
> /* 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)) {
> + remove_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 +695,82 @@ 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 rhltable nfs4_file_rhltable ____cacheline_aligned_in_smp;
> +
> +/*
> + * 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)
> +{
> + u32 k;
> +
> + k = ((unsigned long)inode) >> L1_CACHE_SHIFT;
> + return jhash2(&k, 1, seed);
> +}
>
> -static unsigned int file_hashval(struct svc_fh *fh)
> +/**
> + * 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 - Success; item matches 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 +4314,8 @@ 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 +4333,6 @@ 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 +4685,75 @@ 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 rhlist_head *tmp, *list;
> + struct nfs4_file *fi = NULL;
>
> - 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;
> + list = rhltable_lookup(&nfs4_file_rhltable, fhp,
> + nfs4_file_rhash_params);
> + rhl_for_each_entry_rcu(fi, tmp, list, fi_rhash)
> + if (fh_match(&fi->fi_fhandle, &fhp->fh_handle)) {
> + if (!refcount_inc_not_zero(&fi->fi_ref))
> + fi = NULL;
> + break;
> }
> - }
> - return NULL;
> + return fi;
> }
>
> -static struct nfs4_file *insert_file(struct nfs4_file *new, struct svc_fh *fh,
> - unsigned int hashval)
> +/*
> + * On hash insertion, identify entries with the same inode but
> + * distinct filehandles. They will all be in the same hash bucket
> + * because we hash by the address of the nfs4_file's struct inode.
> + */
> +static struct nfs4_file *insert_file(struct nfs4_file *new,
> + const struct svc_fh *fhp)
> {
> - struct nfs4_file *fp;
> - struct nfs4_file *ret = NULL;
> - bool alias_found = false;
> + struct rhlist_head *tmp, *list;
> + struct nfs4_file *fi;
> + int err;
>
> 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;
> +
> + err = rhltable_insert_key(&nfs4_file_rhltable, fhp,
> + &new->fi_rhash,
> + nfs4_file_rhash_params);
> + if (err) {
> + spin_unlock(&state_lock);
> + return NULL;
> }
> +
> + list = rhltable_lookup(&nfs4_file_rhltable, fhp,
> + nfs4_file_rhash_params);
> + rhl_for_each_entry_rcu(fi, tmp, list, fi_rhash)
> + if (fi->fi_inode == d_inode(fhp->fh_dentry) &&
> + !fh_match(&fi->fi_fhandle, &fhp->fh_handle)) {
> + fi->fi_aliased = true;
> + new->fi_aliased = true;
> + }
> +
> spin_unlock(&state_lock);
> - return ret;
> + return new;
> }
>
> -static struct nfs4_file * find_file(struct svc_fh *fh)
> +static noinline struct nfs4_file *
> +insert_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;
> + /* Do not hash the same filehandle more than once */
> + fi = find_nfs4_file(fhp);
> + if (unlikely(fi))
> + return fi;
> +
> + init_nfs4_file(fhp, new);
> + return insert_file(new, fhp);
> }
>
> -static struct nfs4_file *
> -find_or_add_file(struct nfs4_file *new, struct svc_fh *fh)
> +static noinline void remove_nfs4_file(struct nfs4_file *fi)
> {
> - 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;
> -
> - return insert_file(new, fh, hashval);
> + rhltable_remove(&nfs4_file_rhltable, &fi->fi_rhash,
> + nfs4_file_rhash_params);
> }
>
> /*
> @@ -4703,9 +4766,12 @@ 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);
> + rcu_read_lock();
> + fp = find_nfs4_file(current_fh);
> + rcu_read_unlock();
> if (!fp)
> return ret;
> +
> /* Check for conflicting share reservations */
> spin_lock(&fp->fi_lock);
> if (fp->fi_share_deny & deny_type)
> @@ -5548,7 +5614,11 @@ 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);
> + rcu_read_lock();
> + fp = insert_nfs4_file(open->op_file, current_fh);
> + rcu_read_unlock();
It'd probably be better to push this rcu_read_lock down into
insert_nfs4_file. You don't need to hold it over the actual insertion,
since that requires the state_lock.
> + if (unlikely(!fp))
> + return nfserr_jukebox;
> if (fp != open->op_file) {
> status = nfs4_check_deleg(cl, open, &dp);
> if (status)
> @@ -7905,10 +7975,16 @@ nfs4_state_start(void)
> {
> int ret;
>
> - ret = nfsd4_create_callback_queue();
> + ret = rhltable_init(&nfs4_file_rhltable, &nfs4_file_rhash_params);
> if (ret)
> return ret;
>
> + ret = nfsd4_create_callback_queue();
> + if (ret) {
> + rhltable_destroy(&nfs4_file_rhltable);
> + return ret;
> + }
> +
> set_max_delegations();
> return 0;
> }
> @@ -7939,6 +8015,7 @@ nfs4_state_shutdown_net(struct net *net)
>
> nfsd4_client_tracking_exit(net);
> nfs4_state_destroy_net(net);
> + rhltable_destroy(&nfs4_file_rhltable);
> #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..ad20467c9dee 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 rhlist_head fi_rhash;
> struct list_head fi_stateids;
> union {
> struct list_head fi_delegations;
>
>
--
Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
