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Date: Sun, 15 Jun 2008 13:11:12 +0200
From: Kris Kennaway <kris@FreeBSD.org>
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To: Dmitry Morozovsky <marck@rinet.ru>
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Cc: Kostik Belousov <kostikbel@gmail.com>, delphij@freebsd.org,
	current@freebsd.org
Subject: Re: tmpfs panic
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Dmitry Morozovsky wrote:
> On Sun, 15 Jun 2008, Kostik Belousov wrote:
> 
> KB> On Sun, Jun 15, 2008 at 01:06:24PM +0400, Dmitry Morozovsky wrote:
> KB> > Hi there,
> KB> > 
> KB> > at contemporary RELENG_7/amd64
> 
> [snip]
> 
> 
> KB> I suspect this may be my mistake.
> KB> IN case you can reproduce it, please, try the patch below.
> 
> Will try, thank you. 
> 
> KB> > Also, active tmpfs usage easy leads to "swap zone exhausted, increase
> KB> > kern.maxswzone", even with 2G RAM + 4G swap and approx 2-3G of tmpfs
> KB> > in use -- any hints?
> KB> 
> KB> I think the message is pretty much self-explanatory. Kernel tried to
> KB> allocate the meatadata to track the swap metadata, and zone appears
> KB> exhausted. It is not the swap space shortage. Instead, this is kernel
> KB> zone used to track swap allocation shortage.
> KB> 
> KB> It is quite non-obvious how to automatically tune this limit, since zone
> KB> is allocated before swap is configured.
> 
> Well, but loader(8) man page said:
>   The default of 32MB allows the kernel to support a maximum of ~7GB of swap. 
> 
> and I have only 4G, and system freezes with maxswzone exaustion well before 
> that...

I think swap zone memory use is dependent on the allocation pattern 
(i.e. load dependent), so "a maximum" of 7GB might be the best case 
scenario (or it could be wrong, e.g. on amd64).  This is one of the 
factors that makes it hard to tune the value of maxswzone.

Kris