Re: [PATCH v7 11/14] NFSD: Clean up find_or_add_file()

[Jeff Layton <jlayton@kernel.org>]

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@oracle.com>
> Reviewed-by: NeilBrown <neilb@suse.de>
> ---
>  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@kernel.org>