On Fri, 2022-10-28 at 10:47 -0400, Chuck Lever wrote:
> Remove the call to find_file_locked() in insert_nfs4_file(). Tracing
> shows that over 99% of these calls return NULL. Thus it is not worth
> the expense of the extra bucket list traversal. insert_file() already
> deals correctly with the case where the item is already in the hash
> bucket.
>
> Since nfsd4_file_hash_insert() is now just a wrapper around
> insert_file(), move the meat of insert_file() into
> nfsd4_file_hash_insert() and get rid of it.
>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> Reviewed-by: NeilBrown <neilb@xxxxxxx>
> ---
> fs/nfsd/nfs4state.c | 64 ++++++++++++++++++++++-----------------------------
> 1 file changed, 28 insertions(+), 36 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 504455cb80e9..b1988a46fb9b 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -4683,24 +4683,42 @@ find_file_locked(const struct svc_fh *fh, unsigned int hashval)
> return NULL;
> }
>
> -static struct nfs4_file *insert_file(struct nfs4_file *new, struct svc_fh *fh,
> - unsigned int hashval)
> +static struct nfs4_file * find_file(struct svc_fh *fh)
> {
> struct nfs4_file *fp;
> + unsigned int hashval = file_hashval(fh);
> +
> + rcu_read_lock();
> + fp = find_file_locked(fh, hashval);
> + rcu_read_unlock();
> + return fp;
> +}
> +
> +/*
> + * On hash insertion, identify entries with the same inode but
> + * distinct filehandles. They will all be in the same hash bucket
> + * because nfs4_file's are hashed by the address in the fi_inode
> + * field.
> + */
> +static noinline_for_stack struct nfs4_file *
> +nfsd4_file_hash_insert(struct nfs4_file *new, const struct svc_fh *fhp)
> +{
> + unsigned int hashval = file_hashval(fhp);
> struct nfs4_file *ret = NULL;
> bool alias_found = false;
> + struct nfs4_file *fi;
>
> spin_lock(&state_lock);
> - hlist_for_each_entry_rcu(fp, &file_hashtbl[hashval], fi_hash,
> + hlist_for_each_entry_rcu(fi, &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 (fh_match(&fi->fi_fhandle, &fhp->fh_handle)) {
> + if (refcount_inc_not_zero(&fi->fi_ref))
> + ret = fi;
> + } else if (d_inode(fhp->fh_dentry) == fi->fi_inode)
> + fi->fi_aliased = alias_found = true;
Would it not be better to do the inode comparison first? That's just a
pointer check vs. a full memcmp. That would allow you to quickly rule
out any entries that match different inodes but that are on the same
hash chain.
> }
> if (likely(ret == NULL)) {
> - nfsd4_file_init(fh, new);
> + nfsd4_file_init(fhp, new);
> hlist_add_head_rcu(&new->fi_hash, &file_hashtbl[hashval]);
> new->fi_aliased = alias_found;
> ret = new;
> @@ -4709,32 +4727,6 @@ static struct nfs4_file *insert_file(struct nfs4_file *new, struct svc_fh *fh,
> return ret;
> }
>
> -static struct nfs4_file * find_file(struct svc_fh *fh)
> -{
> - struct nfs4_file *fp;
> - unsigned int hashval = file_hashval(fh);
> -
> - rcu_read_lock();
> - fp = find_file_locked(fh, hashval);
> - rcu_read_unlock();
> - return fp;
> -}
> -
> -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);
> -
> - rcu_read_lock();
> - fp = find_file_locked(fh, hashval);
> - rcu_read_unlock();
> - if (fp)
> - return fp;
> -
> - return insert_file(new, fh, hashval);
> -}
> -
> static noinline_for_stack void nfsd4_file_hash_remove(struct nfs4_file *fi)
> {
> hlist_del_rcu(&fi->fi_hash);
> @@ -5625,7 +5617,7 @@ 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 = nfsd4_file_hash_insert(open->op_file, current_fh);
> if (fp != open->op_file) {
> status = nfs4_check_deleg(cl, open, &dp);
> if (status)
>
>
--
Jeff Layton <jlayton@xxxxxxxxxx>
