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

Solofo.Ramangalahy
2008-06-25T06:21:32Z

Manfred Spraul writes:
> > 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.

Ok, the choice of a maximum value of 65536 which is already is use for
several months/years was made partly for the same concern.
Beside, as the values are not enforced, we should be relatively safe.

Searching the archives, I also found usage of a value "around a MB".

> 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].

Thanks for this information. I should add that I checked that no
regression was introduced with ltp-full-20080531, but I did not look
more closely (e.g. coverage of this part of the code).

--
solofo