> On Oct 31, 2022, at 12:43 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>
> 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.
Marginally better: The usual case after the rhltable changes are
applied is that the returned list contains only entries that match
d_inode(fhp->fh_dentry), and usually that list has just one entry
in it that matches the FH.
Since 11/14 is billed as a clean-up, I'd prefer to put that kind
of optimization in a separate patch that can be mechanically
reverted if need be. I'll post something that goes on top of this
series.
>> }
>> 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>
--
Chuck Lever
