Re: [PATCH] RFC: Use memops for mem paging, sharing, and access, instead of domctls

[Tim Deegan <tim@xen.org>]

At 13:42 -0500 on 11 Jan (1326289372), Andres Lagar-Cavilla wrote:
> Per page operations in the paging, sharing, and access tracking subsystems are
> all implemented with domctls (e.g. a domctl to evict one page, or to share one
> page).
> 
> Under heavy load, the domctl path reveals a lack of scalability. The domctl
> lock serializes dom0's vcpus in the hypervisor. When performing thousands of
> per-page operations on dozens of domains, these vcpus will spin in the
> hypervisor. Beyond the aggressive locking, an added inefficiency of blocking vcpus
> in the domctl lock is that dom0 is prevented from re-scheduling.
> 
> In this proposal we retain the domctl interface for setting up and tearing down
> paging/sharing/mem access for a domain. But we migrate all the per page operations
> to use the memory_op hypercalls (e.g XENMEM_*).
> 
> While we naturally welcome comments on the correctness of the approach, we are also
> concerned about the viability of this API change. With 4.2 coming, this is the right
> time to get an interface right, for the long run.

I'm happy with the API change but I'd like the other users of it to
comment.

Tim.