the property will allow user to specify number of threads to use
in pre-allocation stage. It also will allow to reduce implicit
hostmem dependency on current_machine.
On object creation it will default to 1, but via machine
compat property it will be updated to MachineState::smp::cpus
to keep current behavior for hostmem and main RAM (which is
now also hostmem based).

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
 include/sysemu/hostmem.h |  2 ++
 backends/hostmem.c       | 43 +++++++++++++++++++++++++++++++++++++++----
 vl.c                     | 15 +++++++++++----
 3 files changed, 52 insertions(+), 8 deletions(-)

diff --git a/include/sysemu/hostmem.h b/include/sysemu/hostmem.h
index 5db0d66..bdf8666 100644
--- a/include/sysemu/hostmem.h
+++ b/include/sysemu/hostmem.h
@@ -61,6 +61,7 @@ struct HostMemoryBackendClass {
  * @parent: opaque parent object container
  * @size: amount of memory backend provides
  * @mr: MemoryRegion representing host memory belonging to backend
+ * @prealloc_threads: number of threads to be used for preallocatining RAM
  */
 struct HostMemoryBackend {
     /* private */
@@ -70,6 +71,7 @@ struct HostMemoryBackend {
     uint64_t size;
     bool merge, dump, use_canonical_path;
     bool prealloc, force_prealloc, is_mapped, share;
+    uint32_t prealloc_threads;
     DECLARE_BITMAP(host_nodes, MAX_NODES + 1);
     HostMemPolicy policy;
 
diff --git a/backends/hostmem.c b/backends/hostmem.c
index e773bdf..4c23c77 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -223,7 +223,6 @@ static void host_memory_backend_set_prealloc(Object *obj, bool value,
 {
     Error *local_err = NULL;
     HostMemoryBackend *backend = MEMORY_BACKEND(obj);
-    MachineState *ms = MACHINE(qdev_get_machine());
 
     if (backend->force_prealloc) {
         if (value) {
@@ -243,7 +242,7 @@ static void host_memory_backend_set_prealloc(Object *obj, bool value,
         void *ptr = memory_region_get_ram_ptr(&backend->mr);
         uint64_t sz = memory_region_size(&backend->mr);
 
-        os_mem_prealloc(fd, ptr, sz, ms->smp.cpus, &local_err);
+        os_mem_prealloc(fd, ptr, sz, backend->prealloc_threads, &local_err);
         if (local_err) {
             error_propagate(errp, local_err);
             return;
@@ -252,14 +251,45 @@ static void host_memory_backend_set_prealloc(Object *obj, bool value,
     }
 }
 
+static void host_memory_backend_get_prealloc_threads(Object *obj, Visitor *v,
+    const char *name, void *opaque, Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(obj);
+    visit_type_uint32(v, name, &backend->prealloc_threads, errp);
+}
+
+static void host_memory_backend_set_prealloc_threads(Object *obj, Visitor *v,
+    const char *name, void *opaque, Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(obj);
+    Error *local_err = NULL;
+    uint32_t value;
+
+    visit_type_uint32(v, name, &value, &local_err);
+    if (local_err) {
+        goto out;
+    }
+    if (value <= 0) {
+        error_setg(&local_err,
+                   "property '%s' of %s doesn't take value '%d'",
+                   name, object_get_typename(obj), value);
+        goto out;
+    }
+    backend->prealloc_threads = value;
+out:
+    error_propagate(errp, local_err);
+}
+
 static void host_memory_backend_init(Object *obj)
 {
     HostMemoryBackend *backend = MEMORY_BACKEND(obj);
     MachineState *machine = MACHINE(qdev_get_machine());
 
+    /* TODO: convert this compat properties */
     backend->merge = machine_mem_merge(machine);
     backend->dump = machine_dump_guest_core(machine);
     backend->prealloc = mem_prealloc;
+    backend->prealloc_threads = 1;
 }
 
 static void host_memory_backend_post_init(Object *obj)
@@ -313,7 +343,6 @@ host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
 {
     HostMemoryBackend *backend = MEMORY_BACKEND(uc);
     HostMemoryBackendClass *bc = MEMORY_BACKEND_GET_CLASS(uc);
-    MachineState *ms = MACHINE(qdev_get_machine());
     Error *local_err = NULL;
     void *ptr;
     uint64_t sz;
@@ -378,7 +407,7 @@ host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
          */
         if (backend->prealloc) {
             os_mem_prealloc(memory_region_get_fd(&backend->mr), ptr, sz,
-                            ms->smp.cpus, &local_err);
+                            backend->prealloc_threads, &local_err);
             if (local_err) {
                 goto out;
             }
@@ -456,6 +485,12 @@ host_memory_backend_class_init(ObjectClass *oc, void *data)
         host_memory_backend_set_prealloc, &error_abort);
     object_class_property_set_description(oc, "prealloc",
         "Preallocate memory", &error_abort);
+    object_class_property_add(oc, "prealloc-threads", "int",
+        host_memory_backend_get_prealloc_threads,
+        host_memory_backend_set_prealloc_threads,
+        NULL, NULL, &error_abort);
+    object_class_property_set_description(oc, "prealloc-threads",
+        "Number of CPU threads to use for prealloc", &error_abort);
     object_class_property_add(oc, "size", "int",
         host_memory_backend_get_size,
         host_memory_backend_set_size,
diff --git a/vl.c b/vl.c
index 4ee14f6..61501cc 100644
--- a/vl.c
+++ b/vl.c
@@ -2814,8 +2814,7 @@ static void configure_accelerators(const char *progname)
     }
 }
 
-static void create_default_memdev(MachineState *ms, const char *path,
-                                  bool prealloc)
+static void create_default_memdev(MachineState *ms, const char *path)
 {
     Object *obj;
     MachineClass *mc = MACHINE_GET_CLASS(ms);
@@ -2824,7 +2823,6 @@ static void create_default_memdev(MachineState *ms, const char *path,
     if (path) {
         object_property_set_str(obj, path, "mem-path", &error_fatal);
     }
-    object_property_set_bool(obj, prealloc, "prealloc", &error_fatal);
     object_property_set_int(obj, ms->ram_size, "size", &error_fatal);
     object_property_add_child(object_get_objects_root(), mc->default_ram_id,
                               obj, &error_fatal);
@@ -3967,6 +3965,15 @@ int main(int argc, char **argv, char **envp)
         exit(1);
     }
 
+    if (mem_prealloc) {
+        static GlobalProperty p[] = {
+            {"memory-backend", "prealloc-threads", NULL},
+        };
+
+        p[0].value = g_strdup_printf("%d", current_machine->smp.cpus);
+        compat_props_add(machine_class->compat_props, p, G_N_ELEMENTS(p));
+    }
+
     /*
      * Get the default machine options from the machine if it is not already
      * specified either by the configuration file or by the command line.
@@ -4297,7 +4304,7 @@ int main(int argc, char **argv, char **envp)
     if (numa_uses_legacy_mem() &&
         machine_class->default_ram_size &&
         !current_machine->ram_memdev) {
-        create_default_memdev(current_machine, mem_path, mem_prealloc);
+        create_default_memdev(current_machine, mem_path);
     }
     /* do monitor/qmp handling at preconfig state if requested */
     main_loop();
-- 
2.7.4