Re: [Qemu-devel] [RFC PATCH qemu 0/4] memory: Reduce memory use

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Alexey Kardashevskiy (aik@ozlabs.ru) wrote:
> This was inspired by https://bugzilla.redhat.com/show_bug.cgi?id=1481593
> 
> What happens ithere is that every virtio block device creates 2 address
> spaces - for modern config space (called "virtio-pci-cfg-as") and
> for busmaster (common pci thing, called after the device name,
> in my case "virtio-blk-pci").
> 
> Each address_space_init() updates topology for every address space.
> Every topology update (address_space_update_topology()) creates a new
> dispatch tree - AddressSpaceDispatch with nodes (1KB) and
> sections (48KB) and destroys the old one.
> 
> However the dispatch destructor is postponed via RCU which does not
> get a chance to execute until the machine is initialized but before
> we get there, memory is not returned to the pool, and this is a lot
> of memory which grows n^2.
> 
> These patches are trying to address the memory use and boot time
> issues but tbh only the first one provides visible outcome.

Do you have a feel for how much memory is saved?

Dave

> There are still things to polish and double check the use of RCU,
> I'd like to get any feedback before proceeding - is this going
> the right way or way too ugly?
> 
> 
> This is based on sha1
> 1ab5eb4efb Peter Maydell "Update version for v2.10.0 release".
> 
> Please comment. Thanks.
> 
> 
> 
> Alexey Kardashevskiy (4):
>   memory: Postpone flatview and dispatch tree building till all devices
>     are added
>   memory: Prepare for shared flat views
>   memory: Share flat views and dispatch trees between address spaces
>   memory: Add flat views to HMP "info mtree"
> 
>  include/exec/memory-internal.h |   6 +-
>  include/exec/memory.h          |  93 +++++++++----
>  exec.c                         | 242 +++++++++++++++++++--------------
>  hw/alpha/typhoon.c             |   2 +-
>  hw/dma/rc4030.c                |   4 +-
>  hw/i386/amd_iommu.c            |   2 +-
>  hw/i386/intel_iommu.c          |   9 +-
>  hw/intc/openpic_kvm.c          |   2 +-
>  hw/pci-host/apb.c              |   2 +-
>  hw/pci/pci.c                   |   3 +-
>  hw/ppc/spapr_iommu.c           |   4 +-
>  hw/s390x/s390-pci-bus.c        |   2 +-
>  hw/vfio/common.c               |   6 +-
>  hw/virtio/vhost.c              |   6 +-
>  memory.c                       | 299 +++++++++++++++++++++++++++--------------
>  monitor.c                      |   3 +-
>  vl.c                           |   4 +
>  hmp-commands-info.hx           |   7 +-
>  18 files changed, 448 insertions(+), 248 deletions(-)
> 
> -- 
> 2.11.0
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK