netdev - Re: [PATCH 4/4 (resent) net-2.6.25][UNIX] Make the unix sysctl tables per-namespace

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Date:	Sat, 01 Dec 2007 16:19:43 +0300
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	"Denis V. Lunev" <den@...nvz.org>,
	Herbert Xu <herbert@...dor.apana.org.au>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Linux Containers <containers@...ts.osdl.org>,
	Daniel Lezcano <dlezcano@...ibm.com>
Subject: Re: [PATCH 4/4 (resent) net-2.6.25][UNIX] Make the unix sysctl tables
 per-namespace

Denis V. Lunev wrote:
> Herbert Xu wrote:
>> On Fri, Nov 30, 2007 at 07:37:28PM +0300, Pavel Emelyanov wrote:
>>> Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>
>> All applied to net-2.6.25.
>>
>>> diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
>>> index b0cf075..f97b2a4 100644
>>> --- a/include/net/net_namespace.h
>>> +++ b/include/net/net_namespace.h
>>> @@ -41,6 +43,7 @@ struct net {
>>>  
>>>  	/* unix sockets */
>>>  	int			sysctl_unix_max_dgram_qlen;
>>> +	struct ctl_table_header	*unix_ctl;
>>>  };
>> But I gotta say this struct/file is going to be enormous.  It's also
>> one of those files that causes everything to get recompiled.  Maybe
>> we ought to make a rule that each subsystem only gets to have at most
>> one entry in it :)
>>
>> Thanks,
> 
> Good point, thanks. We'll start thinking in that direction. Right now it
> is not finally cursed with all staff around.

Agree, the point is good :) but it has one pitfall :(

Look, now we make _one_ dereference to get any net->xxx variable 
(sysctl, list head, lock, etc). When we force each subsystem 
has it's "private" pointer on this, we'll make them take _two_ 
dereferences. Before the whole net namespace stuff started we
made _zero_ dereferences :) This may tell upon the performance.

I'm not claiming that this is the major case against this idea,
but when developing this idea, I think we should keep that fact
in ming and pay good attention to performance regressions.

> Regards,
> 	Den

Thanks,
Pavel

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