netdev - Re: [PATCH net 1/2] rhashtable: unconditionally grow when max

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Message-ID: <54EDFC02.2070206@iogearbox.net>
Date:	Wed, 25 Feb 2015 17:44:50 +0100
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Thomas Graf <tgraf@...g.ch>
CC:	davem@...emloft.net, pablo@...filter.org, johunt@...mai.com,
	kaber@...sh.net, netdev@...r.kernel.org,
	Ying Xue <ying.xue@...driver.com>
Subject: Re: [PATCH net 1/2] rhashtable: unconditionally grow when max_shift
 is not specified

On 02/25/2015 05:36 PM, Daniel Borkmann wrote:
> On 02/25/2015 05:28 PM, Thomas Graf wrote:
...
>> I assume you wanted this chunk in patch 2.
>
> No, it's in this chunk on purpose. ;)
>
> I've tried to explain it here in the commit message:
>
>    Given that the test case verifies shrinks/expands manually, we also
>    must remove pointer to the helper functions to explicitly avoid
>    parallel resizing on insertions/deletions. test_bucket_stats() and
>    test_rht_lookup() could also be wrapped around rhashtable mutex to
>    explicitly synchronize a walk from resizing, but I think that defeats
>    the actual test case which intended to have explicit test steps,
>    i.e. 1) inserts, 2) expands, 3) shrinks, 4) deletions, with object
>    verification after each stage.

Note, the reason of this exercise is, because the semantics of
max_shift == 0 have changed. A resize on inserts _before_ this
change was impossible, now it becomes possible, so we have to
disallow resizes (only) for the test case module specifically.
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