Re: Calculating the required value of "ulimit -q"

["Iñaki Baz Castillo" <ibc@aliax.net>]

El Jueves, 14 de Enero de 2010, Eric Wong escribió:
> Iñaki Baz Castillo <ibc@aliax.net> wrote:
> > Hi, I create a mqueue with msgsize 1024 and maxmsg 5000, so in total:
> >
> >   5120000 bytes
> >
> > I set for root that value:
> >
> >   ~# ulimit -q 5120000
> >
> > However I get Errno::ENOMEM. In order it to work I must increase the
> > ulimit to a value closed to 5160000.
> >
> > Could I know which is the exact algorithm to calculate the required
> > "ulimit - q" value based on the desired msgsize and maxmsg?
> > I would like my application to suggest that value if it cannot start due
> > to memory limitations when creating the mqueue.
> 
> Hi Iñaki,
> 
> Under Linux, "man 2 getrlimit" says this:
> 
>   RLIMIT_MSGQUEUE (Since Linux 2.6.8)
>         Specifies the limit on the number of bytes that can be allocated
>         for POSIX message queues for the real user  ID  of  the  calling
>         process.	 This  limit is enforced for mq_open(3).  Each message
>         queue that the user creates counts (until it is removed) against
>         this limit according to the formula:
> 
>         bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
>                 attr.mq_maxmsg * attr.mq_msgsize
> 
>         where  attr  is  the  mq_attr  structure specified as the fourth
>         argument to mq_open(3).
> 
>         The first addend in the formula,	which  includes  sizeof(struct
>         msg_msg *) (4 bytes on Linux/i386), ensures that the user cannot
>         create an unlimited number of zero-length  messages  (such  mes
>         sages nevertheless each consume some system memory for bookkeep
>         ing overhead).

Great, I was looking in the wrong place :)


> I'm not sure about other OSes (info/research/experiences would be
> greatly appreciated!).

Unfortunatelly I just use Linux :)
 
Thanks a lot.

-- 
Iñaki Baz Castillo <ibc@aliax.net>