Re: [Qemu-devel] RFC migration of zero pages

[Avi Kivity]

On Thu, Jan 31, 2013 at 4:30 PM, Gleb Natapov <address@hidden> wrote:
>> >
>> > Avi/Michael do you remember why mincore can't be used to check if a guest
>> page is unmapped?
>>
>> A page may be not in core, but also nonzero (for example swap).
> Yes, mincore() should not be used as zero page check, but it can be used
> as an indicator that page can be dealt with in dead stage of migration
> since it is likely zero and will not take much time to send.

Or it's swapped, in which case we know nothing about it.

> It is
> possible to call madvise(MADV_WILLNEED) on them meanwhile to pre-load
> swap without faulting on each page individually.

During migration you're faulting like mad anyway.