[PATCH 0 of 4] Handling of (some) low memory conditions

[Andres Lagar-Cavilla <andres@lagarcavilla.org>]

After some experiments with the sharing code under low memory conditions, we
post the following series:
- Bugfix sharing unshare when we run out of memory.
- Sort out the situations in which we can go to sleep on a wait queue
 if unshare fails (and by extension the semantics of unshare error
 handling)
- Prevent a certain Ocaml-based toolstack from crashing domains doing sharing
 or paging.
- Add a VIRQ that the hypervisor can emit when reaching a low memory threshold.

Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
Signed-off-by: Adin Scannell <adin@scannell.ca>

 xen/common/domctl.c               |   8 +++++-
 xen/arch/x86/mm/mem_event.c       |   5 ++-
 xen/include/asm-x86/mem_event.h   |  30 ++++++++++++++++++---
 xen/arch/x86/hvm/hvm.c            |  20 +++++++++++++-
 xen/arch/x86/mm.c                 |   8 +++--
 xen/arch/x86/mm/mem_sharing.c     |  52 ++++++++++++++++++++++++---------------
 xen/arch/x86/mm/p2m.c             |  18 ++++++++++++-
 xen/common/grant_table.c          |  11 ++++---
 xen/common/memory.c               |   1 +
 xen/include/asm-x86/mem_sharing.h |  15 +++++++++++
 xen/common/page_alloc.c           |  10 +++++++
 xen/include/public/xen.h          |   1 +
 12 files changed, 140 insertions(+), 39 deletions(-)