netdev - Re: Ottawa and slow hash-table resize

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Date:	Mon, 23 Feb 2015 18:15:44 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	alexei.starovoitov@...il.com
Cc:	paulmck@...ux.vnet.ibm.com, tgraf@...g.ch, josh@...htriplett.org,
	herbert@...dor.apana.org.au, kaber@...sh.net,
	ying.xue@...driver.com, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org
Subject: Re: Ottawa and slow hash-table resize

From: Alexei Starovoitov <alexei.starovoitov@...il.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.
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