> On Jun 22, 2022, at 8:38 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
>
> On Wed, Jun 22, 2022 at 10:15:56AM -0400, Chuck Lever wrote:
>> Enable the filecache hash table to start small, then grow with the
>> workload. Smaller server deployments benefit because there should
>> be lower memory utilization. Larger server deployments should see
>> improved scaling with the number of open files.
>>
>> I know this is a big and messy patch, but there's no good way to
>> rip out and replace a data structure like this.
>>
>> Suggested-by: Jeff Layton <jlayton@xxxxxxxxxx>
>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>
> Pretty sure I mentioned converting to rhashtable as well when we
> were talking about the pointer-chasing overhead of list and tree
> based indexing of large caches. :)
Jeff's suggestion was right in the source code :-) but fair enough.
The idea was also discussed when the filecache code was changed to
use kzvalloc recently.
I appreciate your review and your advice!
>> +
>> +/*
>> + * Atomically insert a new nfsd_file item into nfsd_file_rhash_tbl.
>> + *
>> + * Return values:
>> + * %NULL: @new was inserted successfully
>> + * %A valid pointer: @new was not inserted, a matching item is returned
>> + * %ERR_PTR: an unexpected error occurred during insertion
>> + */
>> +static struct nfsd_file *nfsd_file_insert(struct nfsd_file *new)
>> +{
>> + struct nfsd_file_lookup_key key = {
>> + .type = NFSD_FILE_KEY_FULL,
>> + .inode = new->nf_inode,
>> + .need = new->nf_flags,
>> + .net = new->nf_net,
>> + .cred = current_cred(),
>> + };
>> + struct nfsd_file *nf;
>> +
>> + nf = rhashtable_lookup_get_insert_key(&nfsd_file_rhash_tbl,
>> + &key, &new->nf_rhash,
>> + nfsd_file_rhash_params);
>> + if (!nf)
>> + return nf;
>
> The insert can return an error (e.g. -ENOMEM) so need to check
> IS_ERR(nf) here as well.
That is likely the cause of the BUG that Wang just reported, as
that will send a ERR_PTR to nfsd_file_get(), which blows up when
it tries to defererence it.
I'll resend the series first thing tomorrow morning after some
more clean up and testing.
--
Chuck Lever
