[zfs-discuss] Memory Usage

Al Hopper
Tue, 12 Sep 2006 21:13:56 -0000

On Tue, 12 Sep 2006, Mark Maybee wrote:

> Thomas Burns wrote:
> > Hi,
> >
> > We have been using zfs for a couple of months now, and, overall,
really
> > like it.  However, we have run into a major problem -- zfs''s
memory
> > requirements
> > crowd out our primary application.  Ultimately, we have to reboot the
> > machine
> > so there is enough free memory to start the application.
> >
> > What I would like is:
> >
> > 1) A way to limit the size of the cache (a gig or two would be fine
for
> > us)
> >
> > 2) A way to clear the caches -- hopefully, something faster than
rebooting
> > the machine.
> >
> > Is there any way I can do either of these things?
> >
> > Thanks,
> > Tom Burns
>
> Tom,
>
> What version of solaris are you running?  In theory, ZFS should not
> be hogging your system memory to the point that it crowds out your
> primary applications... but this is still an area that we are working
> out the kinks in.  If you could provide a core dump of the machine
> when it gets to the point that you can''t start your app, it would
> help us.
>
> As to your questions; I will give you some ways to do these things,
> but these are not considered best practice:
>
> 1) You should be able to limit your cache max size by setting
> arc.c_max.  Its currently initialized to be phys-mem-size - 1GB.
>
> 2) First try unmount/remounting your file system to clear the
> cache.  If that doesn''t work, try exporting/importing your pool.

Another nasty and risky workaround is to start making copies of a large
file in /tmp while watching your available swap space carefully.  When you
hit the low memory water mark, ZFS will free up a snitload (technical term
(TM)) of memory.  Then immediately rm all the files you created in /tmp.
You don''t want to completely exhaust memory or you''ll probably
loose the
system.

Remember my first line: "nasty and risky".

Regards,

Al Hopper  Logical Approach Inc, Plano, TX.  al at logical-approach.com
           Voice: 972.379.2133 Fax: 972.379.2134  Timezone: US CDT
OpenSolaris.Org Community Advisory Board (CAB) Member - Apr 2005
                OpenSolaris Governing Board (OGB) Member - Feb 2006