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

[Stefan Hajnoczi]

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 address@hidden 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