Re: Ottawa and slow hash-table resize

[David Miller <davem@davemloft.net>]

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date: Mon, 23 Feb 2015 15:07:20 -0800

> Also 'count of pending inserts' is going to be very small and
> meaningless, since it will count the number of threads that
> are sleeping on insert and not very useful to predict future
> expansions.

Good point.

A way around this would be to allow batching.  So netfilter would
do something like:

	set->ops->batch_insert_start();
	nla_for_each_nested(attr, nla[NFTA_SET_ELEM_LIST_ELEMENTS], rem) {
		err = nft_add_set_elem(&ctx, set, attr);
		if (err < 0)
			break;

		set->nelems++;
	}
	set->ops->batch_insert_end();

And batch_insert_start and batch_insert_end would point to something
that calls new routines rhashtable_batch_insert_start() and
rhashtable_batch_insert_end().

Inside of this sequence, rhashtable_insert() calls queue to a list if
a table grow is in progress.

The pending list is processed by both rhashtable_batch_insert_end()
and table grow completion.