Re: [Qemu-devel] [RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast (de)inflating & fast live migration

[Li, Liang Z]

> On 10/26/2016 03:06 AM, Li, Liang Z wrote:
> > I am working on Dave's new bitmap schema, I have finished the part of
> > getting the 'hybrid scheme bitmap' and found the complexity was more
> > than I expected. The main issue is more memory is required to save the
> > 'hybrid scheme bitmap' beside that used to save the raw page bitmap,
> > for the worst case, the memory required is 3 times than that in the
> > previous implementation.
> 
> Really?  Could you please describe the scenario where this occurs?
> > I am wondering if I should continue, as an alternative solution, how
> > about using PFNs array when inflating/deflating only a few pages?
> > Things will be much more simple.
> 
> Yes, using pfn lists is more efficient than using bitmaps for sparse bitmaps.
> Yes, there will be cases where it is preferable to just use pfn lists vs. any 
> kind
> of bitmap.
> 
> But, what does it matter?  At least with your current scheme where we go
> out and collect get_unused_pages(), we do the allocation up front.  The
> space efficiency doesn't matter at all for small sizes since we do the 
> constant-
> size allocation *anyway*.
> 
> I'm also pretty sure you can pack the pfn and page order into a single 64-bit
> word and have no bitmap for a given record.  That would make it pack just as
> well as the old pfns alone.  Right?

Yes, thanks for reminding, I am using 128 bit now, I will change it to 64 bit.
Let me finish the v4 first.

Thanks!
Liang