diff --git a/src/njs.h b/src/njs.h
index 38819ecfd..4e1c844e7 100644
--- a/src/njs.h
+++ b/src/njs.h
@@ -290,6 +290,8 @@ typedef njs_int_t (*njs_iterator_handler_t)(njs_vm_t *vm,
 
 
 NJS_EXPORT void njs_vm_opt_init(njs_vm_opt_t *options);
+NJS_EXPORT njs_vm_t *njs_vm_create_parent(njs_vm_opt_t *options,
+    njs_vm_t *vm_parent);
 NJS_EXPORT njs_vm_t *njs_vm_create(njs_vm_opt_t *options);
 NJS_EXPORT void njs_vm_destroy(njs_vm_t *vm);
 
diff --git a/src/njs_atom.h b/src/njs_atom.h
index 9ece3a20e..fa8283101 100644
--- a/src/njs_atom.h
+++ b/src/njs_atom.h
@@ -35,5 +35,6 @@ void njs_atom_hash_init(void);
 
 extern njs_atom_values_t  njs_atom;
 extern njs_flathsh_t      njs_atom_hash;
+extern uint32_t           njs_atom_hash_atom_id;
 
 #endif /* _NJS_ATOM_H_INCLUDED_ */
diff --git a/src/njs_builtin.c b/src/njs_builtin.c
index 754cf84bb..e69793002 100644
--- a/src/njs_builtin.c
+++ b/src/njs_builtin.c
@@ -108,7 +108,7 @@ njs_object_hash_init(njs_vm_t *vm, njs_lvlhsh_t *hash,
 
 
 njs_int_t
-njs_builtin_objects_create(njs_vm_t *vm)
+njs_builtin_objects_create(njs_vm_t *vm, njs_vm_t *vm_parent)
 {
     njs_int_t                  ret, index;
     njs_uint_t                 i;
@@ -127,10 +127,31 @@ njs_builtin_objects_create(njs_vm_t *vm)
     vm->shared = shared;
 
     njs_lvlhsh_init(&shared->keywords_hash);
+
     njs_lvlhsh_init(&shared->values_hash);
 
     njs_atom_hash_init();
 
+    if (vm_parent == NULL) {
+        /* njs_lvlhsh_init(&vm->atom_hash_shared); // done by zalign */
+
+        ret = njs_flathsh_alloc_copy(vm->mem_pool, &vm->atom_hash,
+                                     &njs_atom_hash);
+        if (njs_slow_path(ret != NJS_OK)) {
+            return NJS_ERROR;
+        }
+        vm->atom_hash_mem_pool = vm->mem_pool;
+        vm->atom_hash_atom_id = njs_atom_hash_atom_id;
+
+    } else {
+        vm->atom_hash_shared = vm_parent->atom_hash_shared;
+
+        vm->atom_hash = vm_parent->atom_hash;
+        vm->atom_hash_mem_pool = vm_parent->mem_pool;
+        vm->atom_hash_atom_id = vm_parent->atom_hash_atom_id;
+
+    }
+
     pattern = njs_regexp_pattern_create(vm, (u_char *) "(?:)",
                                         njs_length("(?:)"), 0);
     if (njs_slow_path(pattern == NULL)) {
diff --git a/src/njs_flathsh.c b/src/njs_flathsh.c
index c823c4660..c48fec4fd 100644
--- a/src/njs_flathsh.c
+++ b/src/njs_flathsh.c
@@ -573,3 +573,31 @@ njs_flathsh_each(const njs_flathsh_t *fh, njs_flathsh_each_t *fhe)
 
     return NULL;
 }
+
+
+njs_int_t
+njs_flathsh_alloc_copy(njs_mp_t *mp, njs_flathsh_t *to, njs_flathsh_t *from)
+{
+    void                *from_chunk, *to_chunk;
+    uint32_t            from_size;
+    njs_flathsh_descr_t *from_descr;
+
+    from_descr = from->slot;
+
+    from_size = sizeof(uint32_t) * (from_descr->hash_mask + 1ul) +
+                sizeof(njs_flathsh_descr_t) +
+                sizeof(njs_flathsh_elt_t) * from_descr->elts_size;
+
+    to_chunk = njs_mp_alloc(mp, from_size);
+    if (njs_slow_path(to_chunk == NULL)) {
+        return NJS_ERROR;
+    }
+
+    from_chunk = njs_flathsh_chunk(from_descr);
+
+    memcpy(to_chunk, from_chunk, from_size);
+
+    to->slot = (char *)to_chunk + ((char *)from_descr - (char *)from_chunk);
+
+    return NJS_OK;
+}
diff --git a/src/njs_flathsh.h b/src/njs_flathsh.h
index d347bb813..a69792314 100644
--- a/src/njs_flathsh.h
+++ b/src/njs_flathsh.h
@@ -132,6 +132,9 @@ NJS_EXPORT njs_flathsh_elt_t *njs_flathsh_add_elt(njs_flathsh_t *fh,
 NJS_EXPORT njs_flathsh_descr_t *njs_flathsh_new(njs_flathsh_query_t *fhq);
 NJS_EXPORT void njs_flathsh_destroy(njs_flathsh_t *fh, njs_flathsh_query_t *fhq);
 
+NJS_EXPORT njs_int_t njs_flathsh_alloc_copy(njs_mp_t *mp, njs_flathsh_t *to,
+    njs_flathsh_t *from);
+
 
 /* Temporary backward compatibility .*/
 
diff --git a/src/njs_main.h b/src/njs_main.h
index 09a0d1dcb..8715f4ac3 100644
--- a/src/njs_main.h
+++ b/src/njs_main.h
@@ -25,11 +25,11 @@
 #include <njs_murmur_hash.h>
 #include <njs_trace.h>
 #include <njs_queue.h>
-#include <njs_flathsh.h>
 #include <njs_random.h>
 #include <njs_malloc.h>
 #include <njs_rbtree.h>
 #include <njs_mp.h>
+#include <njs_flathsh.h>
 #include <njs_arr.h>
 #include <njs_chb.h>
 #include <njs_utils.h>
diff --git a/src/njs_vm.c b/src/njs_vm.c
index 4c6c0bbd5..ea04157fa 100644
--- a/src/njs_vm.c
+++ b/src/njs_vm.c
@@ -29,7 +29,7 @@ njs_vm_opt_init(njs_vm_opt_t *options)
 
 
 njs_vm_t *
-njs_vm_create(njs_vm_opt_t *options)
+njs_vm_create_parent(njs_vm_opt_t *options, njs_vm_t *vm_parent)
 {
     njs_mp_t      *mp;
     njs_vm_t      *vm;
@@ -62,12 +62,14 @@ njs_vm_create(njs_vm_opt_t *options)
         vm->shared = options->shared;
 
     } else {
-        ret = njs_builtin_objects_create(vm);
+        ret = njs_builtin_objects_create(vm, vm_parent);
         if (njs_slow_path(ret != NJS_OK)) {
             return NULL;
         }
     }
 
+//vm->is_cloned = 0; //??
+
     vm->external = options->external;
 
     vm->spare_stack_size = options->max_stack_size;
@@ -148,6 +150,13 @@ njs_vm_create(njs_vm_opt_t *options)
 }
 
 
+njs_vm_t *
+njs_vm_create(njs_vm_opt_t *options)
+{
+    return njs_vm_create_parent(options, NULL);
+}
+
+
 njs_int_t
 njs_vm_ctor_push(njs_vm_t *vm)
 {
@@ -408,6 +417,13 @@ njs_vm_clone(njs_vm_t *vm, njs_external_ptr_t external)
     nvm->trace.data = nvm;
     nvm->external = external;
 
+    nvm->atom_hash_shared = vm->atom_hash;
+
+    njs_lvlhsh_init(&nvm->atom_hash);
+    nvm->atom_hash_mem_pool = nvm->mem_pool;
+    nvm->atom_hash_atom_id = vm->atom_hash_atom_id;
+//??    nvm->is_clone = 1;
+
     ret = njs_vm_runtime_init(nvm);
     if (njs_slow_path(ret != NJS_OK)) {
         goto fail;
diff --git a/src/njs_vm.h b/src/njs_vm.h
index 6d09caf8f..c4cd12510 100644
--- a/src/njs_vm.h
+++ b/src/njs_vm.h
@@ -128,6 +128,11 @@ struct njs_vm_s {
     njs_native_frame_t       *top_frame;
     njs_frame_t              *active_frame;
 
+    njs_lvlhsh_t             atom_hash_shared;
+    njs_lvlhsh_t             atom_hash;
+    njs_mp_t                 *atom_hash_mem_pool;
+    uint32_t                 atom_hash_atom_id;
+
     njs_lvlhsh_t             keywords_hash;
     njs_lvlhsh_t             values_hash;
 
@@ -243,7 +248,7 @@ void njs_vm_constructors_init(njs_vm_t *vm);
 njs_value_t njs_vm_exception(njs_vm_t *vm);
 void njs_vm_scopes_restore(njs_vm_t *vm, njs_native_frame_t *frame);
 
-njs_int_t njs_builtin_objects_create(njs_vm_t *vm);
+njs_int_t njs_builtin_objects_create(njs_vm_t *vm, njs_vm_t *vm_parent);
 njs_int_t njs_builtin_match_native_function(njs_vm_t *vm,
     njs_function_t *function, njs_str_t *name);