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From: John Baldwin <jhb@freebsd.org>
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	(bigwig.baldwin.cx); Mon, 02 Jul 2012 11:04:34 -0400 (EDT)
Cc: "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net>, current@freebsd.org
Subject: Re: swp_pager_meta_build DoS printf
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On Sunday, July 01, 2012 8:23:31 am Bjoern A. Zeeb wrote:
> Hey,
> 
> hitting this printf in swp_pager_meta_build()
> 
>                         if (uma_zone_exhausted(swap_zone)) {
>                                 printf("swap zone exhausted, increase kern.maxswzone\n");
>                                 vm_pageout_oom(VM_OOM_SWAPZ);
>                                 pause("swzonex", 10);
>                         } else
> 
> seems to be an effective way to put the machine into a state of no recovery
> unless the memory situation would be able to clear itself.  Not that it wouldn't
> otherwise be any better but in addition having a couple of tenthousands of these
> going to console as well is really not helpful to try to do anything either.  Can
> we make it a log() call or something?
> 
> /bz
> 
> PS: I am not sure as I have seen it on someone else's machines and it's
> probably been ZFS that caused it.  I unfortunately neither had a way to
> get back in or break to a kernel debugger, so information is sparse.

This used to be a silent deadlock before I added the printf() and the call to
OOM. :-P  Do you just want to ratelimit the printf?  We have an API to ratelimit
printf's already.

-- 
John Baldwin