Message-ID: <48621A01.8090803@bull.net>
Date: Wed, 25 Jun 2008 12:12:17 +0200
From: Nadia Derbey <Nadia.Derbey@bull.net>
Organization: BULL/DT/OSwR&D/Linux
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To: Manfred Spraul <manfred@colorfullife.com>
Cc: Solofo.Ramangalahy@bull.net, linux-kernel@vger.kernel.org,
       Matt Helsley <matthltc@us.ibm.com>, Mingming Cao <cmm@us.ibm.com>,
       Yasunori Goto <y-goto@jp.fujitsu.com>
Subject: Re: [RFC -mm 0/6] sysv ipc: scale msgmnb with the number of cpus
References: <20080605145712.116223941@bull.net> <484A9D52.2020703@colorfullife.com> <18527.41440.273383.388943@frecb006361.adech.frec.bull.fr> <48613635.70103@colorfullife.com>
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Manfred Spraul wrote:
> Solofo.Ramangalahy@bull.net wrote:
> 
>> Humm... now this make me think that you did not change the MSGMNB
>> value when you changed MSGMNI and MSGMAX.
>> Maybe that was on purpose?
>>
>>   
> 
> I was afraid that it might break user space applications that queue a 
> few kb of messages.
> That's also the reason for
> 
>>                 if (msgsz + msq->q_cbytes <= msq->q_qbytes &&
>>                                 1 + msq->q_qnum <= msq->q_qbytes) {
>>                         break;
>>                 }
> 
> It's possible to send 0-byte messages even if the  message queue is full 
> [except that you can't send more than MSGMNB messages].
> 

Manfred,

If I'm not missign anything when reading the code, sending up to MSGMNB 
0-bytes messages would make us enqueue MSGMNB msg_msg structures (this 
is in the worst case where no receiver is waiting for those messages).
==> MSGMNB * 24 bytes (or 48 bytes in 64-bit mode))
==> 384 KB with current MSGMNB value (16K).

But 1,5 MB with a MSGMNB=64K

Even if it is a worst case, it should be considered and may be we should 
refine the formula Solofo has proposed if you think this is not a 
reasonable value.
May be add a dependency on the memory size?

Regards,
Nadia
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