RE: [PATCH v4 10/14] migration: add support to migrate shared regions list

[Wang, Wei W]

On Friday, September 10, 2021 4:48 PM, Ashish Kalra wrote:
> On Fri, Sep 10, 2021 at 07:54:10AM +0000, Wang, Wei W wrote:
> There has been a long discussion on this implementation on KVM mailing list.
> Tracking shared memory via a list of ranges instead of using bitmap is more
> optimal. Most of the guest memory will be private and the unencrypted/shared
> regions are basically ranges/intervals, so easy to implement and maintain 
> using
> lists.

OK. At which version did you discuss this or do you have a link? (I didn't find 
it in v9 KVM patches)

> A list will consume much less memory than a bitmap.
> 
> The bitmap will consume more memory as it will need to be sized as per guest
> RAM size and will remain sparsely populated due to limited amount of
> shared/unencrypted guest memory regions.

I also thought about this. It depends on the guest.
I think "A list will consume much less memory" is true when we assume most of 
guest pages are private pages.
>From design perspective, what if guest chooses to have most of its pages being 
>shared?
Lists might consume much more memory than bitmaps in some cases, I think.
(Probably I can check your previous discussions first)

Best,
Wei