qemu: Allow prealloc for virtio-mem-pci

There are a some scenarios in which we want to prealloc guest
memory (e.g. when requested in domain XML, when using hugepages,
etc.). With 'regular' <memory/> models (like 'dimm', 'nvdimm' or
'virtio-pmem') or regular guest memory it is corresponding
memory-backend-* object that ends up with .prealloc attribute
set. And that's desired because neither of those devices can
change its size on the fly. However, with virtio-mem model things
are a bit different. While one can set .prealloc attribute on
corresponding memory-backend-* object it doesn't make much sense,
because virtio-mem can inflate/deflate on the fly, i.e. change
how big of a portion of the memory-backend-* object is exposed to
the guest. For instance, from a say 4GiB module only a half can
be exposed to the guest. Therefore, it doesn't make much sense to
preallocate whole 4GiB and keep them allocated. But we still want
the part exposed to the guest preallocated (when conditions
described at the beginning are met).

Having said that, with new enough QEMU the virtio-mem-pci device
gained new attribute ".prealloc" which instructs the device to
talk to the memory backend object and allocate only the requested
portion of memory.

Now, that our algorithm for setting .prealloc was isolated in a
single function, the function can be called when constructing cmd
line for virtio-mem-pci device.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 49f7d27aa3b5fca742bb5c98bb7da1684d6bd4d7..fc778901d19a0b32b84cee51ba066a03e9c341f6 100644 (file)
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -3692,10 +3692,14 @@ qemuBuildMemoryGetPagesize(virQEMUDriverConfig *cfg,
         prealloc = true;
     }
 
-    *pagesizeRet = pagesize;
-    *needHugepageRet = needHugepage;
-    *useHugepageRet = useHugepage;
-    *preallocRet = prealloc;
+    if (pagesizeRet)
+        *pagesizeRet = pagesize;
+    if (needHugepageRet)
+        *needHugepageRet = needHugepage;
+    if (useHugepageRet)
+        *useHugepageRet = useHugepage;
+    if (preallocRet)
+        *preallocRet = prealloc;
 
     return 0;
 }
@@ -3871,14 +3875,18 @@ qemuBuildMemoryBackendProps(virJSONValue **backendProps,
         return -1;
 
     if (mem->model == VIR_DOMAIN_MEMORY_MODEL_VIRTIO_MEM) {
-        /* Explicitly disable prealloc for virtio-mem as it's not supported
-         * currently. Warn users if their config would result in prealloc. */
-        if (priv->memPrealloc || prealloc) {
-            VIR_WARN("Memory preallocation is unsupported for virtio-mem memory devices");
+        if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_DEVICE_VIRTIO_MEM_PCI_PREALLOC)) {
+            /* Explicitly disable prealloc for virtio-mem if it isn't supported.
+             * Warn users if their config would result in prealloc. */
+            if (priv->memPrealloc || prealloc) {
+                VIR_WARN("Memory preallocation is unsupported for virtio-mem memory devices");
+            }
+
+            if (priv->memPrealloc &&
+                virJSONValueObjectAppendBoolean(props, "prealloc", 0) < 0)
+                return -1;
         }
-        if (priv->memPrealloc &&
-            virJSONValueObjectAppendBoolean(props, "prealloc", 0) < 0)
-            return -1;
+
         if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_MEMORY_BACKEND_RESERVE) &&
             virJSONValueObjectAppendBoolean(props, "reserve", 0) < 0)
             return -1;
@@ -4031,7 +4039,9 @@ qemuBuildMemoryDimmBackendStr(virCommand *cmd,
 
 
 virJSONValue *
-qemuBuildMemoryDeviceProps(const virDomainDef *def,
+qemuBuildMemoryDeviceProps(virQEMUDriverConfig *cfg,
+                           qemuDomainObjPrivate *priv,
+                           const virDomainDef *def,
                            const virDomainMemoryDef *mem)
 {
     g_autoptr(virJSONValue) props = NULL;
@@ -4039,6 +4049,7 @@ qemuBuildMemoryDeviceProps(const virDomainDef *def,
     g_autofree char *uuidstr = NULL;
     virTristateBool unarmed = VIR_TRISTATE_BOOL_ABSENT;
     g_autofree char *memdev = NULL;
+    bool prealloc = false;
 
     if (!mem->info.alias) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
@@ -4062,6 +4073,10 @@ qemuBuildMemoryDeviceProps(const virDomainDef *def,
 
     case VIR_DOMAIN_MEMORY_MODEL_VIRTIO_MEM:
         device = "virtio-mem-pci";
+
+        if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_DEVICE_VIRTIO_MEM_PCI_PREALLOC) &&
+            qemuBuildMemoryGetPagesize(cfg, def, mem, NULL, NULL, NULL, &prealloc) < 0)
+            return NULL;
         break;
 
     case VIR_DOMAIN_MEMORY_MODEL_NONE:
@@ -4089,6 +4104,7 @@ qemuBuildMemoryDeviceProps(const virDomainDef *def,
                               "S:uuid", uuidstr,
                               "T:unarmed", unarmed,
                               "s:memdev", memdev,
+                              "B:prealloc", prealloc,
                               "s:id", mem->info.alias,
                               NULL) < 0)
         return NULL;
@@ -7792,7 +7808,7 @@ qemuBuildMemoryDeviceCommandLine(virCommand *cmd,
         if (qemuBuildMemoryDimmBackendStr(cmd, def->mems[i], def, cfg, priv) < 0)
             return -1;
 
-        if (!(props = qemuBuildMemoryDeviceProps(def, def->mems[i])))
+        if (!(props = qemuBuildMemoryDeviceProps(cfg, priv, def, def->mems[i])))
             return -1;
 
         if (qemuBuildDeviceCommandlineFromJSON(cmd, props, priv->qemuCaps) < 0)

diff --git a/src/qemu/qemu_command.h b/src/qemu/qemu_command.h
index dd981e333ff27720e301ea656d2724f0de3076b4..ba175aff9cca86fce561d86505a94749d6748f5d 100644 (file)
--- a/src/qemu/qemu_command.h
+++ b/src/qemu/qemu_command.h
@@ -153,7 +153,9 @@ int qemuBuildMemoryBackendProps(virJSONValue **backendProps,
                                 bool systemMemory);
 
 virJSONValue *
-qemuBuildMemoryDeviceProps(const virDomainDef *def,
+qemuBuildMemoryDeviceProps(virQEMUDriverConfig *cfg,
+                           qemuDomainObjPrivate *priv,
+                           const virDomainDef *def,
                            const virDomainMemoryDef *mem);
 
 /* Current, best practice */

diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
index f36de2385a209cdf051eaaea4f31e91795dc03b8..6e3a60b2253c47a4bbd962622ff19ee660c9af8f 100644 (file)
--- a/src/qemu/qemu_hotplug.c
+++ b/src/qemu/qemu_hotplug.c
@@ -2400,7 +2400,7 @@ qemuDomainAttachMemory(virQEMUDriver *driver,
 
     objalias = g_strdup_printf("mem%s", mem->info.alias);
 
-    if (!(devprops = qemuBuildMemoryDeviceProps(vm->def, mem)))
+    if (!(devprops = qemuBuildMemoryDeviceProps(cfg, priv, vm->def, mem)))
         goto cleanup;
 
     if (qemuBuildMemoryBackendProps(&props, objalias, cfg,

diff --git a/tests/qemuxml2argvdata/memory-hotplug-virtio-mem.x86_64-latest.args b/tests/qemuxml2argvdata/memory-hotplug-virtio-mem.x86_64-latest.args
index 1d83ec88a84a8543d72fe2b618d013d4e748a3d9..77dbc0c89c601f54f2374c7e093fbef26ea2fe4f 100644 (file)
--- a/tests/qemuxml2argvdata/memory-hotplug-virtio-mem.x86_64-latest.args
+++ b/tests/qemuxml2argvdata/memory-hotplug-virtio-mem.x86_64-latest.args
@@ -21,7 +21,7 @@ XDG_CONFIG_HOME=/tmp/lib/domain--1-QEMUGuest1/.config \
 -object '{"qom-type":"memory-backend-ram","id":"memvirtiomem0","reserve":false,"size":1073741824}' \
 -device '{"driver":"virtio-mem-pci","node":0,"block-size":2097152,"requested-size":536870912,"memdev":"memvirtiomem0","id":"virtiomem0","bus":"pci.0","addr":"0x2"}' \
 -object '{"qom-type":"memory-backend-file","id":"memvirtiomem1","mem-path":"/dev/hugepages2M/libvirt/qemu/-1-QEMUGuest1","reserve":false,"size":2147483648,"host-nodes":[1,2,3],"policy":"bind"}' \
--device '{"driver":"virtio-mem-pci","node":0,"block-size":2097152,"requested-size":1073741824,"memdev":"memvirtiomem1","id":"virtiomem1","bus":"pci.0","addr":"0x3"}' \
+-device '{"driver":"virtio-mem-pci","node":0,"block-size":2097152,"requested-size":1073741824,"memdev":"memvirtiomem1","prealloc":true,"id":"virtiomem1","bus":"pci.0","addr":"0x3"}' \
 -uuid c7a5fdbd-edaf-9455-926a-d65c16db1809 \
 -display none \
 -no-user-config \