Re: [Qemu-devel] [RFC Design Doc]Speed up live migration by skipping free pages

[Michael S. Tsirkin]

On Mon, Apr 18, 2016 at 11:08:31AM +0000, Li, Liang Z wrote:
> Hi Dave,
> 
> I am now working on how to benefit post-copy by skipping the free pages, 
> and I remember you have said we should let the destination know the info
> of free pages so as to avoid request the free pages from the source. 
> 
> We have two solutions:
> 
> a. send the migration dirty page bitmap to destination before post
> copy start, so the destination can decide whether to request the pages or 
> place zero pages by checking the migration dirty page bitmap. The advantage
> is that we can avoid sending the free pages. the disadvantage is that we have 
> to send extra data to destination.
> 
> b. Check the page request on the source side, if it's not a dirty page, send 
> a zero
> page header to the destination.
> 
> What's your opinion about them?
> 
> Liang
> 

Both are ad-hoc solutions imho.

c. put the bitmap in a ramblock, check it on destination before
   requesting pages.

This way it's migrated on-demand.

-- 
MST