stacked unionfs freeze and crash FreeBSD

[David Naylor]

On Thursday 21 January 2010 19:56:15 Andriy Gapon wrote:
> on 21/01/2010 19:52 David Naylor said the following:
> > On Wednesday 20 January 2010 19:16:59 Andriy Gapon wrote:
> >> Double-fault could indicate stack overflow.
> >
> > Thanks, I bumped KSTACK_PAGES to 32 (just to be on the safe side) and it
> > is working fairly well now.  Only crash I have had since was related to
> > tmpfs. So far I have successfully build a port with 59 stacked unionfs (1
> > rw, 58 ro).
> 
> Good that you found a workaround, bad that there is no better way to handle
>  this overflow.  Or, is there?

What would make it easier is having kern.kstack_pages tunable (and having the 
appropriate changes to use that variable).  

I do not know the internals of the kernel but is it possible for unionfs 
(assuming it runs in its own thread) to specify a stack size big enough?.  

It might even be possible to extend unionfs to mount multiple directories onto 
another, at once (thus eliminating the need for multiple mounts).  And 
probably a measurable performance increase?

P.S.  Twice I have had processes freeze, these were restricted to directories 
affected by unionfs mounts.
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