Re: [Xen-devel] Claim mode and HVM PoD interact badly

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Jan 10, 2014 at 03:48:31PM +0000, Wei Liu wrote:
> On Fri, Jan 10, 2014 at 10:41:05AM -0500, Konrad Rzeszutek Wilk wrote:
> > On Fri, Jan 10, 2014 at 03:10:48PM +0000, Wei Liu wrote:
> > > On Fri, Jan 10, 2014 at 09:58:07AM -0500, Konrad Rzeszutek Wilk wrote:
> > > > On Fri, Jan 10, 2014 at 11:59:42AM +0000, Ian Campbell wrote:
> > > > > create ^
> > > > > owner Wei Liu <wei.liu2@xxxxxxxxxx>
> > > > > thanks
> > > > > 
> > > > > On Fri, 2014-01-10 at 11:56 +0000, Wei Liu wrote:
> > > > > > When I have following configuration in HVM config file:
> > > > > >   memory=128
> > > > > >   maxmem=256
> > > > > > and have claim_mode=1 in /etc/xen/xl.conf, xl create fails with
> > > > > > 
> > > > > > xc: error: Could not allocate memory for HVM guest as we cannot 
> > > > > > claim memory! (22 = Invalid argument): Internal error
> > > > > > libxl: error: libxl_dom.c:647:libxl__build_hvm: hvm building failed
> > > > > > libxl: error: libxl_create.c:1000:domcreate_rebuild_done: cannot 
> > > > > > (re-)build domain: -3
> > > > > > libxl: error: libxl_dm.c:1467:kill_device_model: unable to find 
> > > > > > device model pid in /local/domain/82/image/device-model-pid
> > > > > > libxl: error: libxl.c:1425:libxl__destroy_domid: 
> > > > > > libxl__destroy_device_model failed for 82
> > > > > > 
> > > > > > With claim_mode=0, I can sucessfuly create HVM guest.
> > > > > 
> > > > > Is it trying to claim 256M instead of 128M? (although the likelyhood
> > > > 
> > > > No. 128MB actually.
> > > > 
> > > 
> > > Huh? My debug message says otherwise. It tried to claim 248MB (256MB -
> > > 8MB video ram). Did I misread your message...
> > 
> > The 'claim' being the hypercall to set the 'clamp' on how much memory
> > the guest can allocate. This is based on:
> > 
> > 242     unsigned long i, nr_pages = args->mem_size >> PAGE_SHIFT;
> > 
> >   /* try to claim pages for early warning of insufficient memory available 
> > */
> > 337     if ( claim_enabled ) {
> > 343         rc = xc_domain_claim_pages(xch, dom, nr_pages - cur_pages);
> > 
> > Your 'mem_size' is 128MB, cur_pages is 0xc0, so it ends up 'claiming'
> > that the guest only needs 128MB - 768kB.
> 
> No, the nr_pages I saw was 63296 (256MB - 768KB) -- I printed it out.

Then my patch should have made no difference in your case. Odd.

> 
> Wei.

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