Re: [Xen-devel] [PATCH 1/1] xc_domain_restore: Allow QEMU to increase memory

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Apr 14, 2015 at 05:22:31PM +0800, Hongyang Yang wrote:
[...]
> >If I understand correctly, the steps are this:
> >
> >* 'xl create' makes a VM of size $FOO
> >* qemu bumps the size to $FOO+$N
> >* 'xl save' writes $FOO+$N of page data, but the xl config file at the
> >start of the image still says $FOO
> >* 'xl restore' creates a vm of size $FOO, then instructs
> >xc_domain_restore() to put $FOO+$N pages into it.
> >
> >I would argue first, that qemu should not play in this area to start with.
> >
> >However, the real bug here is that the domain configuration written by
> >xl save is inaccurate.
> 
> There's a case like COLO:
> 1. Both Primary/Secondary VM are created first with the same config file
>    which makes a VM of size $FOO
> 2. qemu bumps the size to $FOO+$N
> 3. 'save' writes $FOO+$N of page data
> 4. 'restore' put $FOO+$N pages into $FOO pages which will cause error
> 
> Even if you fix the configuration, the bug still exists because the config
> only been transferred from Primary to Secondary once at the very beginning
> when you execute 'xl remus' command. The problem is how to let the secondary
> (restore) side knows the size change? Through a migration command(which is
> easier in v2 migration) or some other solution?

As I said in my reply to Don, the extra memory can be saved during
domain creation. That would solve this problem.

Wei.

> Form this point of view, I think Don's solution is one way to solve the
> problem.
> 
> >
> >~Andrew
> >.
> >
> 
> -- 
> Thanks,
> Yang.

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