Re: [Qemu-devel] [RFC PATCH RDMA support v4: 03/10] more verbose documentation of the RDMA transport

[Michael R. Hines]

On 03/20/2013 11:55 AM, Michael S. Tsirkin wrote:
> Then, later, in a separate patch, I can implement /dev/pagemap support.
>
> When that's done, RDMA dynamic registration will actually take effect and
> benefit from actually verifying that the page is mapped or not.
>
> - Michael
> Mapped into guest? You mean e.g. for ballooning?

Three scenarios are candidates for mapped checking:

1. anytime the virtual machine has not yet accessed a page (usually 
during the 1st-time boot)
2. Anytime madvise(DONTNEED) happens (for ballooning)
3.  Anytime cgroups kicks out a zero page that was accessed and faulted 
but not dirty that is a clean candidate for unmapping.
       (I did a test that seems to confirm that cgroups is pretty 
"smart" about that)

Basically, anytime the pagemap says "this page is *not* swap and *not* 
mapped
- then the page is not important during the 1st iteration.

On the subsequent iterations, we come along as normal checking the dirty 
bitmap as usual.

- Michael