Re: [Xen-devel] [PATCH 0 of 2] x86/mm: Switch paging/sharing/access per-page ops to memops

[Tim Deegan <tim@xxxxxxx>]

At 15:09 -0500 on 01 Feb (1328108978), 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 any of
> its other work-starved processes.
> 
> 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_*).
> 
> A new tools-only section is added to the public memory.h header.
> 
> This is a backwards-incompatible ABI change. It's been floating on the list 
> for
> a couple weeks now, with no nacks thus far.
> 
> Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla>
> Signed-off-by: Adin Scannell <adin@xxxxxxxxxxx>

For the hypervisor parts, 
Acked-by: Tim Deegan <tim@xxxxxxx>

so this can all go in once the tools parts have been reviewed. 

Tim.

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