Re: [Qemu-devel] Are there plans to achieve ram live Snapshot feature?

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Aug 09, 2013 at 10:20:49AM +0000, Chijianchun wrote:
> Now in KVM, when RAM snapshot, vcpus needs stopped, it is Unfriendly restrictions to users.
> 
> Are there plans to achieve ram live Snapshot feature?
> 
> in my mind, Snapshots can not occupy additional too much memory, So when the memory needs to be changed, the old memory page is needed to flush to the file first.  But flushing to file is too slower than memory,  and when flushing, the vcpu or VM is need to be paused until finished flushing,  so pause...resume...pause...resume............., more and more slower.
> 
> Is this idea feasible? Are there any other thoughts?

A few people have looked at live vmsave or guest RAM snapshots.

The idea that was discussed on qemu-devel@nongnu.org uses fork(2) to
capture the state of guest RAM and then send it back to the parent
process.  The guest is only paused for a brief instant during fork(2)
and can continue to run afterwards.

The child process is a simple loop that sends the contents of guest RAM
back to the parent process over a pipe or writes the memory pages to the
save file on disk.  It performs no logic besides writing out guest RAM.

Stefan