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Date:      Thu, 21 Jan 2010 21:58:07 +0200
From:      David Naylor <naylor.b.david@gmail.com>
To:        Andriy Gapon <avg@icyb.net.ua>
Cc:        freebsd-current@freebsd.org
Subject:   Re: stacked unionfs freeze and crash FreeBSD
Message-ID:  <201001212158.13250.naylor.b.david@gmail.com>
In-Reply-To: <4B58953F.10404@icyb.net.ua>
References:  <201001201543.15818.naylor.b.david@gmail.com> <201001211952.20202.naylor.b.david@gmail.com> <4B58953F.10404@icyb.net.ua>

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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).
>=20
> Good that you found a workaround, bad that there is no better way to hand=
le
>  this overflow.  Or, is there?

What would make it easier is having kern.kstack_pages tunable (and having t=
he=20
appropriate changes to use that variable). =20

I do not know the internals of the kernel but is it possible for unionfs=20
(assuming it runs in its own thread) to specify a stack size big enough?. =
=20

It might even be possible to extend unionfs to mount multiple directories o=
nto=20
another, at once (thus eliminating the need for multiple mounts).  And=20
probably a measurable performance increase?

P.S.  Twice I have had processes freeze, these were restricted to directori=
es=20
affected by unionfs mounts.

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