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


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