diff --git a/process.c b/process.c
index 83c44fdd48..8eee6f772a 100644
--- a/process.c
+++ b/process.c
@@ -1090,6 +1090,21 @@ waitpid_signal(struct waitpid_state *w)
     return FALSE;
 }
 
+// Used for VM memsize reporting. Returns the size of a list of waitpid_state
+// structs. Defined here because the struct definition lives here as well.
+size_t
+rb_vm_memsize_waiting_list(struct list_head *waiting_list)
+{
+    struct waitpid_state *waitpid = 0;
+    size_t size = 0;
+
+    list_for_each(waiting_list, waitpid, wnode) {
+        size += sizeof(struct waitpid_state);
+    }
+
+    return size;
+}
+
 /*
  * When a thread is done using sigwait_fd and there are other threads
  * sleeping on waitpid, we must kick one of the threads out of
diff --git a/thread.c b/thread.c
index 95daed6668..46ae21b589 100644
--- a/thread.c
+++ b/thread.c
@@ -5575,6 +5575,21 @@ rb_check_deadlock(rb_ractor_t *r)
     }
 }
 
+// Used for VM memsize reporting. Returns the size of a list of waiting_fd
+// structs. Defined here because the struct definition lives here as well.
+size_t
+rb_vm_memsize_waiting_fds(struct list_head *waiting_fds)
+{
+    struct waiting_fd *waitfd = 0;
+    size_t size = 0;
+
+    list_for_each(waiting_fds, waitfd, wfd_node) {
+        size += sizeof(struct waiting_fd);
+    }
+
+    return size;
+}
+
 static void
 update_line_coverage(VALUE data, const rb_trace_arg_t *trace_arg)
 {
diff --git a/vm.c b/vm.c
index 634ed15884..cb7007ac13 100644
--- a/vm.c
+++ b/vm.c
@@ -2731,15 +2731,63 @@ ruby_vm_destruct(rb_vm_t *vm)
     return 0;
 }
 
+size_t rb_vm_memsize_waiting_list(struct list_head *waiting_list); // process.c
+size_t rb_vm_memsize_waiting_fds(struct list_head *waiting_fds); // thread.c
+size_t rb_vm_memsize_postponed_job_buffer(); // vm_trace.c
+size_t rb_vm_memsize_workqueue(struct list_head *workqueue); // vm_trace.c
+
+// Used for VM memsize reporting. Returns the size of the at_exit list by
+// looping through the linked list and adding up the size of the structs.
+static size_t
+vm_memsize_at_exit_list(rb_at_exit_list *at_exit)
+{
+    size_t size = 0;
+
+    while (at_exit) {
+        size += sizeof(rb_at_exit_list);
+        at_exit = at_exit->next;
+    }
+
+    return size;
+}
+
+// Used for VM memsize reporting. Returns the size of the builtin function
+// table if it has been defined.
+static size_t
+vm_memsize_builtin_function_table(const struct rb_builtin_function *builtin_function_table)
+{
+    return builtin_function_table == NULL ? 0 : sizeof(struct rb_builtin_function);
+}
+
+// Reports the memsize of the VM struct object and the structs that are
+// associated with it.
 static size_t
 vm_memsize(const void *ptr)
 {
-    size_t size = sizeof(rb_vm_t);
+    rb_vm_t *vm = GET_VM();
+
+    return (
+        sizeof(rb_vm_t) +
+        rb_vm_memsize_waiting_list(&vm->waiting_pids) +
+        rb_vm_memsize_waiting_list(&vm->waiting_grps) +
+        rb_vm_memsize_waiting_fds(&vm->waiting_fds) +
+        rb_st_memsize(vm->loaded_features_index) +
+        rb_st_memsize(vm->loading_table) +
+        rb_st_memsize(vm->ensure_rollback_table) +
+        rb_vm_memsize_postponed_job_buffer() +
+        rb_vm_memsize_workqueue(&vm->workqueue) +
+        rb_st_memsize(vm->defined_module_hash) +
+        vm_memsize_at_exit_list(vm->at_exit) +
+        rb_st_memsize(vm->frozen_strings) +
+        vm_memsize_builtin_function_table(vm->builtin_function_table) +
+        rb_id_table_memsize(vm->negative_cme_table) +
+        rb_st_memsize(vm->overloaded_cme_table)
+    );
 
     // TODO
-    // size += vmobj->ractor_num * sizeof(rb_ractor_t);
-
-    return size;
+    // struct { struct list_head set; } ractor;
+    // void *main_altstack; #ifdef USE_SIGALTSTACK
+    // struct rb_objspace *objspace;
 }
 
 static const rb_data_type_t vm_data_type = {
diff --git a/vm_trace.c b/vm_trace.c
index 466856341d..7f6a60b0cb 100644
--- a/vm_trace.c
+++ b/vm_trace.c
@@ -1578,6 +1578,29 @@ struct rb_workqueue_job {
     rb_postponed_job_t job;
 };
 
+// Used for VM memsize reporting. Returns the size of a list of rb_workqueue_job
+// structs. Defined here because the struct definition lives here as well.
+size_t
+rb_vm_memsize_workqueue(struct list_head *workqueue)
+{
+    struct rb_workqueue_job *work = 0;
+    size_t size = 0;
+
+    list_for_each(workqueue, work, jnode) {
+        size += sizeof(struct rb_workqueue_job);
+    }
+
+    return size;
+}
+
+// Used for VM memsize reporting. Returns the total size of the postponed job
+// buffer that was allocated at initialization.
+size_t
+rb_vm_memsize_postponed_job_buffer()
+{
+    return sizeof(rb_postponed_job_t) * MAX_POSTPONED_JOB;
+}
+
 void
 Init_vm_postponed_job(void)
 {