On Fri, Sep 27, 2024 at 08:48:14AM GMT, Herbert Xu wrote:

On Tue, Sep 24, 2024 at 10:48:07PM -0400, Kent Overstreet wrote:

quoted

I've been noticing rhashtable resize is surprisingly heavy (the default
parameters don't ever shrink the table, which is why it's not seen as
much).

Most rhashtable users enable automatic shrinking.

quoted

And, when I was torture testing that code I tripped over what appeared
to be an infinite loop in rht_bucket() when a rehsah is in progress,
which I worked around in

  a592cdf5164d bcachefs: don't use rht_bucket() in btree_key_cache_scan()

You must not walk the rhashtable internal data structures by hand.
If you need to iterate through the whole table, use the provided
walking mechanism.

I was just doing rht_for_each_entry_rcu() (open coded because you don't
provide a safe version).

However, as rhashtable is dynamic, walking it during a resize may
cause you to see some elements twice.  If you want to avoid that,
set up your own linked list of all elements for a completely stable
walk.

Yeah that's fine, but like I said, I was seeing an infinite loop inside
rht_bucket(). That would be an rhashtable bug...