Re: [Xen-devel] [PATCH v2 for-4.5] libxl: account for romfile memory

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Nov 25, 2014 at 04:56:02PM +0000, Ian Campbell wrote:
> On Tue, 2014-11-25 at 16:49 +0000, Stefano Stabellini wrote:
> > On Tue, 25 Nov 2014, Ian Campbell wrote:
> > > On Tue, 2014-11-25 at 12:43 +0000, Stefano Stabellini wrote:
> > > > Account for the extra memory needed for the rom files of any emulated 
> > > > nics:
> > > > QEMU uses xc_domain_populate_physmap_exact to allocate the memory for
> > > > each them. Assume 256K each.
> > > 
> > > I suppose this will have to do for 4.5. Can we do something better in
> > > the future -- like figuring out a way for guests to have
> > > "not-really-RAM" allocations like this which are made by the toolstack
> > > and happen to be backed by RAM not count or something.
> > > 
> > > > 
> > > > This patch fixes a QEMU abort() when more than 4 emulated nics are
> > > > assigned to a VM.
> > > 
> > > Are you also going to fix qemu to fail gracefully if it cannot deploy
> > > option roms? abort() seems a bit extreme.
> > > 
> > > > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > > > CC: Don Slutz <dslutz@xxxxxxxxxxx>
> > > > CC: hanyandong <hanyandong@xxxxxxxxx>
> > > > CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > > > CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
> > > > CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> > > 
> > > You missed Ian J. I've added him.
> > 
> > Actually Wei suggested a better alternative: I could call
> > xc_domain_setmaxmem directly from QEMU. That makes much more sense.
> 
> xl mem-set would do it again, but not taking qemu's extras into account,
> unless you communicate the overhead somehow...
> 

Use a xenstore key? Like /vm/$UUID/XXX.

The key can be written by QEMU (because it knows the extra ram used by
all ROMs) and read by libxl.

(Haven't followed this closely, just my two cents)

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