Re: [RFC -mm 0/6] sysv ipc: scale msgmnb with the number of cpus

[Nadia Derbey]

Manfred Spraul wrote:
> Solofo.Ramangalahy@xxxxxxxx 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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