Re: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for fast (de)inflating & fast live migration

From: Dave Hansen
Date: Thu Dec 15 2016 - 10:34:40 EST

On 12/14/2016 12:59 AM, Li, Liang Z wrote:
>> Subject: Re: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for
>> fast (de)inflating & fast live migration
>> On 12/08/2016 08:45 PM, Li, Liang Z wrote:
>>> What's the conclusion of your discussion? It seems you want some
>>> statistic before deciding whether to ripping the bitmap from the ABI,
>>> am I right?
>> I think Andrea and David feel pretty strongly that we should remove the
>> bitmap, unless we have some data to support keeping it. I don't feel as
>> strongly about it, but I think their critique of it is pretty valid. I think the
>> consensus is that the bitmap needs to go.
>> The only real question IMNHO is whether we should do a power-of-2 or a
>> length. But, if we have 12 bits, then the argument for doing length is pretty
>> strong. We don't need anywhere near 12 bits if doing power-of-2.
> Just found the MAX_ORDER should be limited to 12 if use length instead of order,
> If the MAX_ORDER is configured to a value bigger than 12, it will make things more
> complex to handle this case.
> If use order, we need to break a large memory range whose length is not the power of 2 into several
> small ranges, it also make the code complex.

I can't imagine it makes the code that much more complex. It adds a for
loop. Right?

> It seems we leave too many bit for the pfn, and the bits leave for length is not enough,
> How about keep 45 bits for the pfn and 19 bits for length, 45 bits for pfn can cover 57 bits
> physical address, that should be enough in the near feature.
> What's your opinion?

I still think 'order' makes a lot of sense. But, as you say, 57 bits is
enough for x86 for a while. Other architectures.... who knows?