Re: [PATCH RFC 04/15] KVM: Implement ring-based dirty memory tracking

Paolo Bonzini
2019-12-14T07:57:32Z

On 13/12/19 21:23, Peter Xu wrote:
>> What is the benefit of using u16 for that? That means with 4K pages, you
>> can share at most 256M of dirty memory each time? That seems low to me,
>> especially since it's sufficient to touch one byte in a page to dirty it.
>>
>> Actually, this is not consistent with the definition in the code ;-)
>> So I'll assume it's actually u32.
> Yes it's u32 now. Actually I believe at least Paolo would prefer u16
> more. :)

It has to be u16, because it overlaps the padding of the first entry.

Paolo

> I think even u16 would be mostly enough (if you see, the maximum
> allowed value currently is 64K entries only, not a big one). Again,
> the thing is that the userspace should be collecting the dirty bits,
> so the ring shouldn't reach full easily. Even if it does, we should
> probably let it stop for a while as explained above. It'll be
> inefficient only if we set it to a too-small value, imho.
>