Re: [Qemu-devel] [RFC PATCH 0/8] MemoryRegion and FlatView refcounting, replace hostmem with memory_region_find

[liu ping fan]

On Mon, May 6, 2013 at 10:25 PM, Paolo Bonzini <address@hidden> wrote:
> Hi,
>
> this is an alternative approach to refactoring of dataplane's HostMem
> code.  Here, I take Ping Fan's idea of RCU-style updating of the
> region list and apply it to the AddressSpace's FlatView.  With this

In fact, I am worrying about the priority of MemoryListener, if it is
true, then we should drop RCU-style idea. Also if it is true, there is
already a bug with hostmem listener. It should use region_del, not
region_nop to reconstruct the local view. But just let me have a deep
thinking.

Regards,
Pingfan
> change, dataplane can simply use memory_region_find instead of
> hostmem.
>
> This is a somewhat larger change, but I prefer it for two reasons.
>
> 1) it splits the task of adding BQL-less memory dispatch in two parts,
>    tacking memory_region_find first (which is simpler because locking
>    is left to the caller).
>
> 2) HostMem duplicates a lot of the FlatView logic, and adding the
>    RCU-style update in FlatView benefits everyone.
>
> The missing ingredients here are:
>
> 1) remember and unreference the MemoryRegions that are used in
>    a vring entry.  In order to implement this, it is probably simpler
>    to change vring.c to use virtio.c's VirtQueueElement data structure.
>    We want something like that anyway in order to support migration.
>
> 2) add an owner field to MemoryRegion, and set it for all MemoryRegions
>    for hot-unpluggable devices.  In this series, ref/unref are stubs.
>
> For simplicity I based the patches on my IOMMU rebase.  I placed the
> tree at git://github.com/bonzini/qemu.git, branch iommu.
>
> Paolo
>
> Paolo Bonzini (8):
>   memory: add ref/unref calls
>   exec: check MRU in qemu_ram_addr_from_host
>   memory: return MemoryRegion from qemu_ram_addr_from_host
>   memory: ref/unref memory across address_space_map/unmap
>   memory: access FlatView from a local variable
>   memory: use a new FlatView pointer on every topology update
>   memory: add reference counting to FlatView
>   dataplane: replace hostmem with memory_region_find
>
>  exec.c                                |   63 +++++++++---
>  hw/core/loader.c                      |    1 +
>  hw/display/exynos4210_fimd.c          |    6 +
>  hw/display/framebuffer.c              |   10 +-
>  hw/i386/kvm/ioapic.c                  |    2 +
>  hw/i386/kvmvapic.c                    |    1 +
>  hw/misc/vfio.c                        |    2 +
>  hw/virtio/dataplane/Makefile.objs     |    2 +-
>  hw/virtio/dataplane/hostmem.c         |  176 
> ---------------------------------
>  hw/virtio/dataplane/vring.c           |   56 +++++++++--
>  hw/virtio/vhost.c                     |    2 +
>  hw/virtio/virtio-balloon.c            |    1 +
>  hw/xen/xen_pt.c                       |    4 +
>  include/exec/cpu-common.h             |    2 +-
>  include/exec/memory.h                 |    9 ++
>  include/hw/virtio/dataplane/hostmem.h |   57 -----------
>  include/hw/virtio/dataplane/vring.h   |    3 +-
>  kvm-all.c                             |    2 +
>  memory.c                              |  142 +++++++++++++++++++++-----
>  target-arm/kvm.c                      |    2 +
>  target-i386/kvm.c                     |    4 +-
>  target-sparc/mmu_helper.c             |    1 +
>  xen-all.c                             |    2 +
>  23 files changed, 253 insertions(+), 297 deletions(-)
>  delete mode 100644 hw/virtio/dataplane/hostmem.c
>  delete mode 100644 include/hw/virtio/dataplane/hostmem.h
>