Re: [PATCH 1 of 3] x86/mm/sharing: Clean ups for relinquishing shared pages on destroy

[Tim Deegan <tim@xen.org>]

At 10:16 -0400 on 12 Apr (1334225772), Andres Lagar-Cavilla wrote:
>  xen/arch/x86/domain.c             |  16 ++++++++++++-
>  xen/arch/x86/mm/mem_sharing.c     |  45 +++++++++++++++++++++++++++++++++++++++
>  xen/arch/x86/mm/p2m.c             |   4 +++
>  xen/include/asm-arm/mm.h          |   4 +++
>  xen/include/asm-x86/domain.h      |   1 +
>  xen/include/asm-x86/mem_sharing.h |  10 ++++++++
>  xen/include/asm-x86/p2m.h         |   4 +++
>  7 files changed, 82 insertions(+), 2 deletions(-)
> 
> 
> When a domain is destroyed, its pages are freed in relinquish_resources in a
> preemptible mode, in the context of a synchronous domctl.
> 
> P2m entries pointing to shared pages are, however, released during p2m cleanup
> in an RCU callback, and in non-preemptible mode.
> 
> This is an O(n) operation for a very large n, which may include actually
> freeing shared pages for which the domain is the last holder.
> 
> To improve responsiveness, move this operation to the preemtible portion of
> domain destruction, during the synchronous domain_kill hypercall. And remove
> the bulk of the work from the RCU callback.
> 
> Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>

I've applied this as a bug-fix.  The other two seem more like new
development and I'm less happy about taking them before 4.2

Cheers,

Tim.