Thus spake Brooks Davis <[EMAIL PROTECTED]>:
> On Wed, Feb 12, 2003 at 07:40:00PM -0800, Terry Lambert wrote:
> > Darren Pilgrim wrote:
> > > Not really.  A properly laid-out filesystem hierarchy will result in no
> > > writes to / (except for installworld/kernel).  That removes the problem
> > > that journalling addresses, and is probably why softupdates is disabled
> > > by default for /.  For large, active filesystems, journalling would be a
> > > big improvement when you had to run a foreground fsck.
> > 
> > Soft updates are disable on / by default because of the chicken
> > and egg problem of runing tunefs on /.
> There's no chicken and egg problem when you're booting off install
> media or for that matter from single user mode.  The problem was that
> softupdates means you don't get space back from deleted files immediatly
> so previously / tended to fillup during installworld or installkernel.
> I know some fixes have been implemented in that area, but I'm not sure
> if then mean you can always write to the space occupied by unlinked
> files or just that you have a better chance.

The problem is effectively fixed in 5.0.  Basically, when no space
can be found, the syncer is accelerated to try to speed up frees.
Technically it's possible to run into a livelock, where you keep
freeing space and it keeps getting snatched up before you can grab
it, so you wait forever.  So IIRC, there is a point where it just
gives up on finding the space.  However, that won't happen with an
install, so the free space problem isn't a reason not to use
softupdates on the root FS.  I think the default hasn't been
changed just because nobody has bothered.

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