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

["Denis V. Lunev" <den@openvz.org>]

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 ballon almost
immediately inflates balloon and effectively kill the guest as
qemu counts nvdimm as part of the ram.

Counting dimm devices as part of the ram for ballooning was started from
patch
 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>
---
The patch is submitted start a discussion. It may be technically correct,
but for us the situation is a bit shady.

 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 b3038b2..613b4d5 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 if should be 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'
           }
 }
 
-- 
2.1.4