Re: [PATCH v2 1/1] tools: Handle xc_maxmem adjustments

From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>,
	Ian Campbell <ian.campbell@citrix.com>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	Don Slutz <dslutz@verizon.com>,
	xen-devel@lists.xen.org, Shriram Rajagopalan <rshriram@cs.ubc.ca>,
	Yang Hongyang <yanghy@cn.fujitsu.com>
Subject: Re: [PATCH v2 1/1] tools: Handle xc_maxmem adjustments
Date: Wed, 15 Apr 2015 10:57:09 +0100	[thread overview]
Message-ID: <alpine.DEB.2.02.1504151054330.7690@kaball.uk.xensource.com> (raw)
In-Reply-To: <552E3509.8010107@citrix.com>

On Wed, 15 Apr 2015, Andrew Cooper wrote:
> On 14/04/15 23:06, Don Slutz wrote:
> > This fixes an issue where "xl save" followed by "xl restore" reports:
> > "xc: error: Failed to allocate memory for batch.!: Internal error"
> >
> > One of the ways to get into this state is to have more then 4 e1000
> > nics configured.
> >
> > Signed-off-by: Don Slutz <dslutz@verizon.com>
> 
> I still don't think this is the correct solution, although I will
> concede that this is a far better patch than v1.
> 
> Going back to the original problem, why does Qemu need to change maxmem
> in the first place?  You talk about e1000 option roms, but the option
> roms themselves must be allocated in an appropriate PCI bridge window.

QEMU allocates actual memory to store the option roms using
xc_domain_populate_physmap_exact, increasing the total amount of ram
allocated to the guest. QEMU needs to increase maxmem too, otherwise
memory allocations will fail after a few option roms.