From owner-freebsd-hackers@freebsd.org  Wed Aug  9 09:53:49 2017
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Subject: Re: Freebsd 11.0 - system freeze on intensive I/O
To: Gautam <list@execve.net>, freebsd-hackers@freebsd.org
References: <CAD9pFYAAy8jKcABNTun-Y3knrbUreQ7q1-CCj=323HgLMC5e6g@mail.gmail.com>
From: Eugene Grosbein <eugen@grosbein.net>
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Date: Wed, 9 Aug 2017 16:52:37 +0700
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09.08.2017 14:11, Gautam пишет:
> Hi,
> 
> I raised this topic on freebsd-questions where I suspect a bug caused due
> to swapfile usage on FreeBSD.
> 
> You could read details in the below thread, but summary is that with using
> a swapfile (not a swap partition) the system freezes on some single process
> intensive I/O. This is 100% reproducible.
> 
> http://marc.info/?l=freebsd-questions&m=150088763825675&w=2
> 
> I raised a PR - 220971 ; but there are no backtraces / logs etc. that could
> possibly help.
> 
> I would like to help narrow this down, but do not know how. Any suggestions
> on how to debug a system freeze and what I need to do ? I could then try to
> reproduce this and collect the needed information - traces etc.

Swapfile is definitely broken in supported FreeBSD releases, it hangs the system.
The only known workaround (to me) is not using it.