Re: md /tmp and async mounts

On 2006-06-01 01:04, Jonathan Noack <noackjr_at_alumni.rice.edu> wrote:
> On 05/31/06 20:20, Giorgos Keramidas wrote:
> > The following diff should be sufficient for enabling -o async for
> > the MFS /tmp and MFS /var filesystems we support in our current
> > rc.d stuff:
> >
> > %%%
> > Index: share/man/man5/rc.conf.5
> > ===================================================================
> > --- share/man/man5/rc.conf.5	(revision 99)
> > +++ share/man/man5/rc.conf.5	(revision 101)
> > _at__at_ -24,7 +24,7 _at__at_
> >  .\"
> >  .\" $FreeBSD: src/share/man/man5/rc.conf.5,v 1.298 2006/05/30 16:20:48 matteo Exp $
> >  .\"
> > -.Dd May 29, 2006
> > +.Dd Jun  1, 2006
> >  .Dt RC.CONF 5
> >  .Os
> >  .Sh NAME
> > _at__at_ -241,12 +241,13 _at__at_
> >  .Pa /tmp
> >  is created.
> >  The default is
> > -.Dq Li "-S -M" ,
> > +.Dq Li "-S -M -o async" ,
> >  which inhibits the use of softupdates on
> >  .Pa /tmp
> >  to waste as little space as possible
> > -and creates a pure memory backed disk, which will never be swapped out,
> > -for maximum performance and system stability at low memory conditions.
> > +and creates a pure memory-backed disk, which uses asynchronous I/O
> > +and will never be swapped out, for maximum performance and system
> > +stability at low memory conditions.
>
> Given recent posts about panics with malloc-backed mds under
> low-memory conditions (see the "kmem leak in tmpmfs?" thread on
> stable_at_), I'm not sure keeping '-M' as the default for tmpmfs
> and varmfs is advisable.  Here is the rather ominous note on
> using malloc-backed mds in mdconfig(8): "Storage for this type
> of memory disk is allocated with malloc(9).  This limits the
> size to the malloc bucket limit in the kernel.  If the -o
> reserve option is not set, creating and filling a large
> malloc-backed memory disk is a very easy way to panic a
> system."

Note that the -M option has *been* already the default for ages.
I am not suggestting to change these options in this patch.