Re: [Qemu-devel] [PATCH v2 1/1] nvdimm: disable balloon

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 25 Jan 2016 19:50:31 +0300
"Denis V. Lunev" <den@openvz.org> wrote:

> From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> 
> NVDIMM for now is planned to use as a backing store for DAX filesystem
> in the guest and thus this memory is excluded from guest memory management
> and LRUs.
> 
> In this case libvirt running QEMU along with configured balloon almost
> immediately inflates balloon and effectively kill the guest as
> qemu counts nvdimm as part of the ram.

Isn't issue in ballooning impl. and not of pc-dimm/nvdimm,
so make ballooning code to distinguish between kinds of memory
rather than adding not related fields to PCDIMMDeviceClass

why don't just move get_current_ram_size() into the sole user
virtio-balloon.c and ignore NVDIMMs when counting ram in
get_current_ram_size(),
that would be much less intrusive patch.

> 
> Counting dimm devices as part of the ram for ballooning was started from
> commit 463756d03:
>  virtio-balloon: Fix balloon not working correctly when hotplug memory
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> CC: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> CC: "Michael S. Tsirkin" <mst@redhat.com>
> CC: Igor Mammedov <imammedo@redhat.com>
> CC: Eric Blake <eblake@redhat.com>
> CC: Markus Armbruster <armbru@redhat.com>
> ---
> v2:
>     - some rewordings, thanks to Eric Blake
> 
>  hw/mem/nvdimm.c          | 4 ++++
>  hw/mem/pc-dimm.c         | 7 ++++++-
>  include/hw/mem/pc-dimm.h | 1 +
>  qapi-schema.json         | 5 ++++-
>  4 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/mem/nvdimm.c b/hw/mem/nvdimm.c
> index 4fd397f..4f4d29a 100644
> --- a/hw/mem/nvdimm.c
> +++ b/hw/mem/nvdimm.c
> @@ -27,9 +27,13 @@
>  static void nvdimm_class_init(ObjectClass *oc, void *data)
>  {
>      DeviceClass *dc = DEVICE_CLASS(oc);
> +    PCDIMMDeviceClass *ddc = PC_DIMM_CLASS(oc);
>  
>      /* nvdimm hotplug has not been supported yet. */
>      dc->hotpluggable = false;
> +
> +    /* ballooning is not supported */
> +    ddc->in_ram = false;
>  }
>  
>  static TypeInfo nvdimm_info = {
> diff --git a/hw/mem/pc-dimm.c b/hw/mem/pc-dimm.c
> index d5cdab2..e0f869d 100644
> --- a/hw/mem/pc-dimm.c
> +++ b/hw/mem/pc-dimm.c
> @@ -164,6 +164,7 @@ int qmp_pc_dimm_device_list(Object *obj, void *opaque)
>              MemoryDeviceInfo *info = g_new0(MemoryDeviceInfo, 1);
>              PCDIMMDeviceInfo *di = g_new0(PCDIMMDeviceInfo, 1);
>              DeviceClass *dc = DEVICE_GET_CLASS(obj);
> +            PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(obj);
>              PCDIMMDevice *dimm = PC_DIMM(obj);
>  
>              if (dev->id) {
> @@ -172,6 +173,7 @@ int qmp_pc_dimm_device_list(Object *obj, void *opaque)
>              }
>              di->hotplugged = dev->hotplugged;
>              di->hotpluggable = dc->hotpluggable;
> +            di->in_ram = ddc->in_ram;
>              di->addr = dimm->addr;
>              di->slot = dimm->slot;
>              di->node = dimm->node;
> @@ -205,7 +207,9 @@ ram_addr_t get_current_ram_size(void)
>          if (value) {
>              switch (value->type) {
>              case MEMORY_DEVICE_INFO_KIND_DIMM:
> -                size += value->u.dimm->size;
> +                if (value->u.dimm->in_ram) {
> +                    size += value->u.dimm->size;
> +                }
>                  break;
>              default:
>                  break;
> @@ -444,6 +448,7 @@ static void pc_dimm_class_init(ObjectClass *oc, void *data)
>      dc->props = pc_dimm_properties;
>      dc->desc = "DIMM memory module";
>  
> +    ddc->in_ram = true;
>      ddc->get_memory_region = pc_dimm_get_memory_region;
>  }
>  
> diff --git a/include/hw/mem/pc-dimm.h b/include/hw/mem/pc-dimm.h
> index d83bf30..3bcb505 100644
> --- a/include/hw/mem/pc-dimm.h
> +++ b/include/hw/mem/pc-dimm.h
> @@ -65,6 +65,7 @@ typedef struct PCDIMMDevice {
>  typedef struct PCDIMMDeviceClass {
>      /* private */
>      DeviceClass parent_class;
> +    bool in_ram;
>  
>      /* public */
>      MemoryRegion *(*get_memory_region)(PCDIMMDevice *dimm);
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 2e960db..3cafa2b 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -3922,6 +3922,8 @@
>  #
>  # @hotpluggable: true if device if could be added/removed while machine is running
>  #
> +# @in-ram: true if device is counted in current ram size (since 2.6)
> +#
>  # Since: 2.1
>  ##
>  { 'struct': 'PCDIMMDeviceInfo',
> @@ -3932,7 +3934,8 @@
>              'node': 'int',
>              'memdev': 'str',
>              'hotplugged': 'bool',
> -            'hotpluggable': 'bool'
> +            'hotpluggable': 'bool',
> +            'in-ram': 'bool'
>            }
>  }
>