Re: xBSD shmem doc deficiency

Apparently only some settings are adjustable.

root(at)dev:~# uname -smr
FreeBSD 4.2-RELEASE i386
root(at)dev:~# sysctl -a | grep kern.ipc.semm
kern.ipc.semmap: 30
kern.ipc.semmni: 10
kern.ipc.semmns: 60
kern.ipc.semmnu: 30
kern.ipc.semmsl: 60
root(at)dev:~# sysctl -w kern.ipc.semmap=50
kern.ipc.semmap: 30 -> 50
root(at)dev:~# sysctl -w kern.ipc.semmni=50
sysctl: oid 'kern.ipc.semmni' is read only
root(at)dev:~#

On 20 Nov 2002, Neil Conway wrote:

> The documentation on changing shared memory kernel settings on xBSD
> (namely FreeBSD, possibly others as well) isn't ideal, IMHO. It says:
>
> %%
> The options SYSVSHM and SYSVSEM need to be enabled when the
> kernel is compiled. (They are by default.) The maximum size of
> shared memory is determined by the option SHMMAXPGS (in
> pages). The following shows an example of how to set the various
> parameters:
>
> options SYSVSHM
> options SHMMAXPGS=4096
> options SHMSEG=256
>
> options SYSVSEM
> options SEMMNI=256
> options SEMMNS=512
> options SEMMNU=256
> options SEMMAP=256
>
> (On NetBSD and OpenBSD the key word is actually option singular.)
>
> You may also want to use the sysctl setting to lock shared memory
> into RAM and prevent it from being paged out to swap.
> %%
>
> However, it appears that shared memory & semaphore settings can also
> be controlled via sysctls -- at least on a FreeBSD 4.7-RELEASE box, I
> can see:
>
> kern.ipc.semmap: 30
> kern.ipc.semmni: 10
> kern.ipc.semmns: 60
> kern.ipc.semmnu: 30
> kern.ipc.semmsl: 60
> kern.ipc.semopm: 100
> kern.ipc.semume: 10
> kern.ipc.semusz: 92
> kern.ipc.semvmx: 32767
> kern.ipc.semaem: 16384
> kern.ipc.shmmax: 33554432
> kern.ipc.shmmin: 1
> kern.ipc.shmmni: 192
> kern.ipc.shmseg: 128
> kern.ipc.shmall: 8192
> kern.ipc.shm_use_phys: 0
>
> However, the FreeBSD box I'm playing with isn't mine, so I'm not too
> keen to change sysctls (well, that and I don't have root :-) ). Would
> a kind BSD user confirm that:
>
> (a) the sysctls above *can* be used to change kernel shared
> memory settings, and the default value of the sysctl is
> the kernel option referred to in the docs.
>
> (b) do the above sysctls work on NetBSD and OpenBSD as well?
>
> (c) the 'prevent shared memory paging' sysctl vaguely referred
> to in the docs is 'kern.ipc.shm_use_phys', right?
>
> (d) does the above sysctl also work on NetBSD and OpenBSD?
>
> Thanks in advance,
>
> Neil
>
> --
> Neil Conway <neilc(at)samurai(dot)com> || PGP Key ID: DB3C29FC
>
>
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