Thread: xBSD shmem doc deficiency
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
maximumsize of shared memory is determined by the option SHMMAXPGS (in pages). The following shows an example of
howto 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
thesysctl 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@samurai.com> || PGP Key ID: DB3C29FC
On 20 Nov 2002, Neil Conway wrote: > 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? A quick look at OpenBSD 3.2 (man 3 sysctl) appears to show that all you can do at runtime is enable/disable message queues, shared memory, and semaphores, not adjust buffer counts or sizes. It seems the kernel must still be recompiled with the desired new settings. Jon
Apparently only some settings are adjustable. root@dev:~# uname -smr FreeBSD 4.2-RELEASE i386 root@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@dev:~# sysctl -w kern.ipc.semmap=50 kern.ipc.semmap: 30 -> 50 root@dev:~# sysctl -w kern.ipc.semmni=50 sysctl: oid 'kern.ipc.semmni' is read only root@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@samurai.com> || PGP Key ID: DB3C29FC > > > ---------------------------(end of broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org >
Neil Conway wrote:
> (c) the 'prevent shared memory paging' sysctl vaguely referred
> to in the docs is 'kern.ipc.shm_use_phys', right?
I have added a mention of this to the 7.4 docs:
You might also want to use the <application>sysctl</> setting to lock shared memory into RAM and prevent
itfrom being paged out to swap, e.g. <literal>kern.ipc.shm_use_phys</>.
-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square,
Pennsylvania19073
Hi Neil, > 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. Unless this has changed in 4.7, lots of those shm sysctls are read-only...ie. you cannot set the shared memory pool size at runtime. I'll look at it again tho. > (c) the 'prevent shared memory paging' sysctl vaguely referred > to in the docs is 'kern.ipc.shm_use_phys', right? I'll have to investigate that one... Chris