netdev - Re: [PATCH net-next 3/5] rhashtable: use future table size to make expansion decision

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Date:	Tue, 6 Jan 2015 17:56:23 +0800
From:	Ying Xue <ying.xue@...driver.com>
To:	Thomas Graf <tgraf@...g.ch>
CC:	<davem@...emloft.net>, <netdev@...r.kernel.org>,
	<jon.maloy@...csson.com>, <Paul.Gortmaker@...driver.com>,
	<erik.hugne@...csson.com>, <tipc-discussion@...ts.sourceforge.net>
Subject: Re: [PATCH net-next 3/5] rhashtable: use future table size to make
 expansion decision

On 01/06/2015 05:35 PM, Thomas Graf wrote:
> On 01/06/15 at 03:23pm, Ying Xue wrote:
>> Should use future table size instead of old table size to decide
>> whether hash table is worth being expanded.
>>
>> Signed-off-by: Ying Xue <ying.xue@...driver.com>
>> Cc: Thomas Graf <tgraf@...g.ch>
>> ---
>>  lib/rhashtable.c |    5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> Apologies as you were probably mislead by the bug as commented
> on in the previous patch.
> 
> I don't think we need this. future_tbl only points to a different
> table until the old table entries are linked from the new table.
> The condition in the resize check where meant to exclude this
> phase so we would newer get to the deferred worker while relinking
> is happening.
> 
> 

Thank you for above nice explanation. Regarding my understanding, as
rhashtable_expand() and rhashtable_shrink() are always under the
protection of "ht->mutex", the "future_tbl" and "tbl" absolutely point
to the same bucket array once rhashtable_expand() or rhashtable_shrink()
returns. Therefore, if rht_deferred_worker() takes the "ht->mutex" lock,
the both "future_tbl" and "tbl" should point to the same bucket array.
So the change made in the patch is useless for us, right?

But as you pointed in above patch, there is a bug in
rhashtable_wakeup_worker(). As long as ht->tbl == ht->future_tbl, we
should wake up the work. OK, I will drop the patch and fix the error in
patch #2.

In all, thank you for quickly reviewing the series, and I would deliver
the next version soon in which your all comments would be resolved.

Please wait a moment.

Regards,
Ying

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