Re: [Qemu-devel] RFC migration of zero pages

[Michael R. hines]

What about using the linux pagemap?

With RDMA, I have exactly this problem. The cost of mapping and faulting 
and checking for zeros is higher than the cost of simply dumping the 
page into remote memory on the server side.
If we could avoid accessing the page, it was save huge amounts of time....

- Michael

On 01/31/2013 02:47 AM, Orit Wasserman wrote:
> We send one byte per zero page at the moment (see is_dup_page) we can 
> further optimizing it by not sending it. I have to point out that this 
> is a very idle guest and we need to work on a loaded guest which is 
> the more hard problem in migration. Also I notice that the bottle neck 
> in migrating unmapped pages is the detection of those pages because we 
> map the pages in order to check them, for a large guest this is very 
> expensive as mapping a page results in a page fault in the host. So 
> what will be very helpful is actually locating those pages without 
> mapping them which looks very complicated. Regards, Orit
> > Peter