From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: XEN 4.0 + 2.6.31.13 pvops kernel : system crashes
	on starting 155th domU
Date: Tue, 27 Apr 2010 09:59:11 -0400
Message-ID: <20100427135911.GB23625@phenom.dumpdata.com>
References: <019701cae5dd$01b36e70$051a4b50$@ucsd.edu>
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To: Yuvraj Agarwal <yuvraj@cs.ucsd.edu>
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On Tue, Apr 27, 2010 at 12:41:07AM -0700, Yuvraj Agarwal wrote:
> Hi All, 
> 
>  
> 
> We are setting up a system with a large number of very small VMs for a
> project. We worked through a number of limitations, including those
> imposed by blktap2 devices and the number of dynamic IRQ (set kernel
> config NR_CPUS) etc. After these changes we were able to get to  154 domUs
> (!), but as soon as we start up the 155th domU the system crashes. We
> edited each domU config to have one blktap2 device (the disk image) and
> two virtual network interfaces each. 

This sounds strangly familiar. I believe somebody posted a question
about this a couple of months ago on the xen-devel mailing list and
found the answer. I think part of it was CONFIG_LEGACY_PTY_COUNT had to
be high. But I don't remember the exact details - you might want to
search the archive.