diff --git a/ocaml/otherlibs/str/str.ml b/ocaml/otherlibs/str/str.ml
index 67b862ad1ad..2fb5de9ea64 100644
--- a/ocaml/otherlibs/str/str.ml
+++ b/ocaml/otherlibs/str/str.ml
@@ -607,16 +607,6 @@ external re_search_forward: regexp -> string -> int -> int array
 external re_search_backward: regexp -> string -> int -> int array
      = "re_search_backward"
 
-module Domain = struct
-  module DLS = struct
-
-    (* CR ocaml 5 domains: Remove this proxy and use the real Domain.DLS *)
-    let[@inline always] new_key f = ref (f ())
-    let[@inline always] set k s = k := s
-    let[@inline always] get k = !k
-  end
-end
-
 let last_search_result_key = Domain.DLS.new_key (fun () -> [||])
 
 let string_match re s pos =
diff --git a/ocaml/runtime/caml/domain.h b/ocaml/runtime/caml/domain.h
index fe555fbe63b..930359bbdcc 100644
--- a/ocaml/runtime/caml/domain.h
+++ b/ocaml/runtime/caml/domain.h
@@ -109,14 +109,14 @@ int caml_try_run_on_all_domains_with_spin_work(
   int sync,
   void (*handler)(caml_domain_state*, void*, int, caml_domain_state**),
   void* data,
-  void (*leader_setup)(caml_domain_state*),
+  void (*leader_setup)(caml_domain_state*, void*),
   /* return nonzero if there may still be useful work to do while spinning */
   int (*enter_spin_callback)(caml_domain_state*, void*),
   void* enter_spin_data);
 int caml_try_run_on_all_domains(
   void (*handler)(caml_domain_state*, void*, int, caml_domain_state**),
   void*,
-  void (*leader_setup)(caml_domain_state*));
+  void (*leader_setup)(caml_domain_state*, void*));
 
 /* Function naming conventions for STW callbacks and STW critical sections.
 
diff --git a/ocaml/runtime/caml/major_gc.h b/ocaml/runtime/caml/major_gc.h
index eea353e6c5d..2a5af67d3e5 100644
--- a/ocaml/runtime/caml/major_gc.h
+++ b/ocaml/runtime/caml/major_gc.h
@@ -30,6 +30,7 @@ extern gc_phase_t caml_gc_phase;
 Caml_inline int caml_marking_started(void) {
   return caml_gc_phase != Phase_sweep_main;
 }
+extern atomic_uintnat caml_gc_mark_phase_requested;
 
 intnat caml_opportunistic_major_work_available (caml_domain_state*);
 void caml_opportunistic_major_collection_slice (intnat);
@@ -45,7 +46,7 @@ void caml_teardown_major_gc(void);
 void caml_darken(void*, value, volatile value* ignored);
 void caml_darken_cont(value);
 void caml_mark_root(value, value*);
-void caml_empty_mark_stack(void);
+void caml_mark_roots_stw(int, caml_domain_state**);
 void caml_finish_major_cycle(int force_compaction);
 #ifdef DEBUG
 int caml_mark_stack_is_empty(void);
diff --git a/ocaml/runtime/caml/minor_gc.h b/ocaml/runtime/caml/minor_gc.h
index 0333340b06d..2d7bf42bab4 100644
--- a/ocaml/runtime/caml/minor_gc.h
+++ b/ocaml/runtime/caml/minor_gc.h
@@ -87,7 +87,7 @@ extern void caml_realloc_ephe_ref_table (struct caml_ephe_ref_table *);
 extern void caml_realloc_custom_table (struct caml_custom_table *);
 struct caml_minor_tables* caml_alloc_minor_tables(void);
 void caml_free_minor_tables(struct caml_minor_tables*);
-void caml_empty_minor_heap_setup(caml_domain_state* domain);
+void caml_empty_minor_heap_setup(caml_domain_state* domain, void*);
 
 #ifdef DEBUG
 extern int caml_debug_is_minor(value val);
diff --git a/ocaml/runtime/domain.c b/ocaml/runtime/domain.c
index eeb4c28285d..8ac41bb1bb4 100644
--- a/ocaml/runtime/domain.c
+++ b/ocaml/runtime/domain.c
@@ -1031,8 +1031,6 @@ struct domain_startup_params {
 
 static void* backup_thread_func(void* v)
 {
-  // single-domain hack
-  caml_fatal_error("backup thread not allowed to run");
   dom_internal* di = (dom_internal*)v;
   uintnat msg;
   struct interruptor* s = &di->interruptor;
@@ -1591,7 +1589,7 @@ int caml_try_run_on_all_domains_with_spin_work(
   int sync,
   void (*handler)(caml_domain_state*, void*, int, caml_domain_state**),
   void* data,
-  void (*leader_setup)(caml_domain_state*),
+  void (*leader_setup)(caml_domain_state*, void*),
   int (*enter_spin_callback)(caml_domain_state*, void*),
   void* enter_spin_data)
 {
@@ -1659,7 +1657,7 @@ int caml_try_run_on_all_domains_with_spin_work(
   }
 
   if( leader_setup ) {
-    leader_setup(domain_state);
+    leader_setup(domain_state, data);
   }
 
 #ifdef DEBUG
@@ -1726,7 +1724,7 @@ int caml_try_run_on_all_domains_with_spin_work(
 int caml_try_run_on_all_domains(
   void (*handler)(caml_domain_state*, void*, int, caml_domain_state**),
   void* data,
-  void (*leader_setup)(caml_domain_state*))
+  void (*leader_setup)(caml_domain_state*, void*))
 {
   return
       caml_try_run_on_all_domains_with_spin_work(1,
@@ -1738,7 +1736,7 @@ int caml_try_run_on_all_domains(
 int caml_try_run_on_all_domains_async(
   void (*handler)(caml_domain_state*, void*, int, caml_domain_state**),
   void* data,
-  void (*leader_setup)(caml_domain_state*))
+  void (*leader_setup)(caml_domain_state*, void*))
 {
   return
       caml_try_run_on_all_domains_with_spin_work(0,
diff --git a/ocaml/runtime/major_gc.c b/ocaml/runtime/major_gc.c
index e9c295dd525..7b283f7a574 100644
--- a/ocaml/runtime/major_gc.c
+++ b/ocaml/runtime/major_gc.c
@@ -156,12 +156,6 @@ static atomic_uintnat num_domains_orphaning_finalisers = 0;
 static atomic_uintnat alloc_counter;
 static atomic_uintnat work_counter;
 
-enum global_roots_status{
-  WORK_UNSTARTED,
-  WORK_STARTED
-};
-static atomic_uintnat domain_global_roots_started;
-
 gc_phase_t caml_gc_phase;
 
 /* The caml_gc_phase global is only ever updated at the end of the STW
@@ -199,6 +193,9 @@ Caml_inline char caml_gc_phase_char(int may_access_gc_phase) {
   }
 }
 
+/* True when some domain wants to enter Phase_sweep_and_mark_main */
+atomic_uintnat caml_gc_mark_phase_requested;
+
 extern value caml_ephe_none; /* See weak.c */
 
 static struct ephe_cycle_info_t {
@@ -324,13 +321,26 @@ static void ephe_todo_list_emptied (void)
 
   /* Since the todo list is empty, this domain does not need to participate in
    * further ephemeron cycles. */
-  atomic_fetch_add(&ephe_cycle_info.num_domains_todo, -1);
+  atomic_fetch_add_verify_ge0(&ephe_cycle_info.num_domains_todo, -1);
   CAMLassert(atomic_load_acquire(&ephe_cycle_info.num_domains_done) <=
              atomic_load_acquire(&ephe_cycle_info.num_domains_todo));
 
   caml_plat_unlock(&ephe_lock);
 }
 
+/* Begin ephemeron marking by making all 'live' ephes become 'todo' */
+static void begin_ephe_marking(void)
+{
+  caml_domain_state* domain = Caml_state;
+  CAMLassert(domain->ephe_info->todo == (value) NULL);
+  domain->ephe_info->todo = domain->ephe_info->live;
+  domain->ephe_info->live = (value) NULL;
+  domain->ephe_info->must_sweep_ephe = 0;
+  domain->ephe_info->cycle = 0;
+  domain->ephe_info->cursor.todop = NULL;
+  domain->ephe_info->cursor.cycle = 0;
+}
+
 /* Record that ephemeron marking was done for the given ephemeron cycle. */
 static void record_ephe_marking_done (uintnat ephe_cycle)
 {
@@ -487,12 +497,16 @@ static int no_orphaned_work (void)
     atomic_load_acquire(&orph_structs.final_info) == NULL;
 }
 
-static void adopt_orphaned_work (void)
+static void adopt_orphaned_work (int expected_status)
 {
   caml_domain_state* domain_state = Caml_state;
   value orph_ephe_list_live, last;
   struct caml_final_info *f, *myf, *temp;
 
+#ifdef DEBUG
+  orph_ephe_list_verify_status(expected_status);
+#endif
+
   if (no_orphaned_work() || caml_domain_is_terminating())
     return;
 
@@ -940,7 +954,7 @@ static intnat mark_stack_push_block(struct mark_stack* stk, value block)
 
 /* This function shrinks the mark stack back to the MARK_STACK_INIT_SIZE size
    and is called at domain termination via caml_finish_marking. */
-void caml_shrink_mark_stack (void)
+static void shrink_mark_stack (void)
 {
   struct mark_stack* stk = Caml_state->mark_stack;
   intnat init_stack_bsize = MARK_STACK_INIT_SIZE * sizeof(mark_entry);
@@ -1179,6 +1193,7 @@ static inline value_ptr chunk_and_offset_to_ptr(uintnat chunk, uintnat offset) {
 /* mark until the budget runs out or marking is done */
 static intnat mark(intnat budget) {
   caml_domain_state *domain_state = Caml_state;
+  CAMLassert(caml_marking_started());
   while (budget > 0 && !domain_state->marking_done) {
     budget = do_some_marking(domain_state->mark_stack, budget);
     if (budget > 0) {
@@ -1382,35 +1397,51 @@ static intnat ephe_sweep (caml_domain_state* domain_state, intnat budget)
   return budget;
 }
 
-static void start_marking (int participant_count, caml_domain_state** barrier_participants)
+static void request_mark_phase (void)
 {
-  caml_domain_state* domain = Caml_state;
-  /* Need to ensure the minor heap is empty before we snapshot the roots,
-     because the minor heap may currently point to UNMARKED major blocks */
-  if (barrier_participants) {
-    caml_empty_minor_heap_no_major_slice_from_stw
-      (domain, (void*)0, participant_count, barrier_participants);
-  } else {
-    caml_empty_minor_heaps_once ();
+  if (caml_gc_phase == Phase_sweep_main &&
+      atomic_load_relaxed(&caml_gc_mark_phase_requested) == 0)
+    atomic_store_release(&caml_gc_mark_phase_requested, 1);
+}
+
+void caml_mark_roots_stw (int participant_count, caml_domain_state** barrier_participants)
+{
+  if (caml_gc_phase != Phase_sweep_main)
+    return;
+
+  enum global_roots_status {
+    WORK_UNSTARTED,
+    WORK_STARTED,
+    WORK_COMPLETE
+  };
+  static atomic_uintnat global_roots_scanned;
+
+  Caml_global_barrier_if_final(participant_count) {
+    caml_gc_phase = Phase_sweep_and_mark_main;
+    atomic_store_relaxed(&global_roots_scanned, WORK_UNSTARTED);
   }
 
-  /* CR ocaml 5 domains (sdolan):
-     Either this transition needs to be synchronised between domains,
-     or a different write barrier needs to be used while some domains
-     have started marking and others have not. */
-  CAMLassert(caml_domain_alone());
-  caml_gc_phase = Phase_sweep_and_mark_main;
+  caml_domain_state* domain = Caml_state;
+
+  /* Adopt orphaned work from domains that were spawned and terminated in the
+     previous cycle. */
+  adopt_orphaned_work (caml_global_heap_state.UNMARKED);
+
+  begin_ephe_marking();
 
   CAML_EV_BEGIN(EV_MAJOR_MARK_ROOTS);
-  caml_do_roots (&caml_darken, darken_scanning_flags, domain, domain, 0);
   {
     uintnat work_unstarted = WORK_UNSTARTED;
-    if(atomic_compare_exchange_strong(&domain_global_roots_started,
-                                      &work_unstarted,
-                                      WORK_STARTED)){
-        caml_scan_global_roots(&caml_darken, domain);
+    if (atomic_load_relaxed(&global_roots_scanned) == WORK_UNSTARTED &&
+        atomic_compare_exchange_strong(&global_roots_scanned,
+                                       &work_unstarted, WORK_STARTED)) {
+      /* This domain did the CAS, so this domain marks the roots */
+      caml_scan_global_roots(&caml_darken, domain);
+      atomic_store_release(&global_roots_scanned, WORK_COMPLETE);
     }
   }
+  /* Locals, C locals, systhreads & finalisers */
+  caml_do_roots (&caml_darken, darken_scanning_flags, domain, domain, 0);
   CAML_EV_END(EV_MAJOR_MARK_ROOTS);
 
   CAML_EV_BEGIN(EV_MAJOR_MEMPROF_ROOTS);
@@ -1421,16 +1452,20 @@ static void start_marking (int participant_count, caml_domain_state** barrier_pa
   caml_gc_log("Marking started, %ld entries on mark stack",
               (long)domain->mark_stack->count);
 
-  if (domain->mark_stack->count == 0 &&
-      !caml_addrmap_iter_ok(&domain->mark_stack->compressed_stack,
-                            domain->mark_stack->compressed_stack_iter)
-      ) {
-    atomic_fetch_add_verify_ge0(&num_domains_to_mark, -1);
-    domain->marking_done = 1;
-  }
-
   if (domain->ephe_info->todo == (value) NULL)
     ephe_todo_list_emptied();
+
+  /* Wait until global roots are marked. It's fine if other domains are still
+     marking their local roots, as long as the globals are done */
+  if (atomic_load_acquire(&global_roots_scanned) != WORK_COMPLETE) {
+    CAML_EV_BEGIN(EV_MAJOR_MARK_OPPORTUNISTIC);
+    SPIN_WAIT {
+      caml_opportunistic_major_collection_slice(1000);
+      if (atomic_load_acquire(&global_roots_scanned) == WORK_COMPLETE)
+        break;
+    }
+    CAML_EV_END(EV_MAJOR_MARK_OPPORTUNISTIC);
+  }
 }
 
 static void cycle_major_heap_from_stw_single(
@@ -1504,10 +1539,11 @@ static void cycle_major_heap_from_stw_single(
   atomic_store_release(&num_domains_to_sweep, num_domains_in_stw);
   atomic_store_release(&num_domains_to_mark, num_domains_in_stw);
 
-      caml_gc_phase = Phase_sweep_main;
-      atomic_store(&ephe_cycle_info.num_domains_todo, num_domains_in_stw);
-      atomic_store(&ephe_cycle_info.ephe_cycle, 1);
-      atomic_store(&ephe_cycle_info.num_domains_done, 0);
+  caml_gc_phase = Phase_sweep_main;
+  atomic_store(&caml_gc_mark_phase_requested, 0);
+  atomic_store(&ephe_cycle_info.num_domains_todo, num_domains_in_stw);
+  atomic_store(&ephe_cycle_info.ephe_cycle, 1);
+  atomic_store(&ephe_cycle_info.num_domains_done, 0);
 
   atomic_store_release(&num_domains_to_ephe_sweep, 0);
   /* Will be set to the correct number when switching to
@@ -1518,8 +1554,6 @@ static void cycle_major_heap_from_stw_single(
   atomic_store_release(&num_domains_to_final_update_last,
                        num_domains_in_stw);
 
-  atomic_store(&domain_global_roots_started, WORK_UNSTARTED);
-
   caml_code_fragment_cleanup_from_stw_single();
 }
 
@@ -1606,21 +1640,6 @@ static void stw_cycle_all_domains(
   domain->sweeping_done = 0;
   domain->marking_done = 0;
 
-  /* Ephemerons */
-#ifdef DEBUG
-  orph_ephe_list_verify_status (caml_global_heap_state.UNMARKED);
-#endif
-  /* Adopt orphaned work from domains that were spawned and terminated in the
-     previous cycle. */
-  adopt_orphaned_work ();
-  CAMLassert(domain->ephe_info->todo == (value) NULL);
-  domain->ephe_info->todo = domain->ephe_info->live;
-  domain->ephe_info->live = (value) NULL;
-  domain->ephe_info->must_sweep_ephe = 0;
-  domain->ephe_info->cycle = 0;
-  domain->ephe_info->cursor.todop = NULL;
-  domain->ephe_info->cursor.cycle = 0;
-
   /* Finalisers */
   domain->final_info->updated_first = 0;
   domain->final_info->updated_last = 0;
@@ -1713,7 +1732,9 @@ static void stw_try_complete_gc_phase(
 
 intnat caml_opportunistic_major_work_available (caml_domain_state* domain_state)
 {
-  return !domain_state->sweeping_done || !domain_state->marking_done;
+  return
+    !domain_state->sweeping_done ||
+    (caml_marking_started() && !domain_state->marking_done);
 }
 
 static char collection_slice_mode_char(collection_slice_mode mode)
@@ -1785,11 +1806,11 @@ static void major_collection_slice(intnat howmuch,
     if (log_events) CAML_EV_END(EV_MAJOR_SWEEP);
   }
 
-  if (domain_state->sweeping_done &&
-      caml_gc_phase == Phase_sweep_main &&
-      get_major_slice_work(mode) > 0 &&
-      mode != Slice_opportunistic) {
-    start_marking(participant_count, barrier_participants);
+  if (domain_state->sweeping_done) {
+    /* We do not immediately trigger a minor GC, but instead wait for
+       the next one to happen normally. This gives some chance that
+       other domains will finish sweeping as well. */
+    request_mark_phase();
   }
 
 
@@ -1830,10 +1851,7 @@ static void major_collection_slice(intnat howmuch,
       /* Nothing has been marked while updating last */
     }
 
-#ifdef DEBUG
-    orph_ephe_list_verify_status (caml_global_heap_state.MARKED);
-#endif
-    adopt_orphaned_work();
+    adopt_orphaned_work(caml_global_heap_state.MARKED);
 
     /* Ephemerons */
     if (caml_gc_phase != Phase_sweep_ephe) {
@@ -2025,8 +2043,10 @@ static void stw_finish_major_cycle (caml_domain_state* domain, void* arg,
      will only terminate when [caml_major_cycles_completed] is
      incremented, and this happens in [cycle_all_domains] inside
      a barrier. */
+  request_mark_phase();
   caml_empty_minor_heap_no_major_slice_from_stw
     (domain, (void*)0, participating_count, participating);
+  CAMLassert (caml_marking_started());
 
   CAML_EV_BEGIN(EV_MAJOR_FINISH_CYCLE);
   while (params.saved_major_cycles == caml_major_cycles_completed) {
@@ -2056,9 +2076,17 @@ int caml_mark_stack_is_empty(void)
 }
 #endif
 
-void caml_empty_mark_stack (void)
+static void empty_mark_stack (void)
 {
   while (!Caml_state->marking_done){
+    /* while, not if: it is possible for caml_empty_minor_heaps_once
+       to actually do a full major GC cycle, and end up returning with
+       caml_marking_started false, because the next cycle has started */
+    while (!caml_marking_started()) {
+      request_mark_phase();
+      /* This calls caml_mark_roots_stw with the minor heap empty */
+      caml_empty_minor_heaps_once();
+    }
     mark(1000);
     caml_handle_incoming_interrupts();
   }
@@ -2073,14 +2101,12 @@ void caml_finish_marking (void)
 {
   if (!Caml_state->marking_done) {
     CAML_EV_BEGIN(EV_MAJOR_FINISH_MARKING);
-    if (!caml_marking_started()) {
-      start_marking(0, NULL);
-    }
-    caml_empty_mark_stack();
-    caml_shrink_mark_stack();
+    empty_mark_stack();
+    shrink_mark_stack();
     Caml_state->stat_major_words += Caml_state->allocated_words;
     Caml_state->allocated_words = 0;
     Caml_state->allocated_words_direct = 0;
+    CAMLassert(Caml_state->marking_done);
     CAML_EV_END(EV_MAJOR_FINISH_MARKING);
   }
 }
@@ -2197,9 +2223,16 @@ int caml_init_major_gc(caml_domain_state* d) {
                   caml_addrmap_iterator(&d->mark_stack->compressed_stack);
 
   /* Fresh domains do not need to performing marking or sweeping. */
-  /* CR ocaml 5 domains: how does this interact with Phase_sweep_main? */
-  d->sweeping_done = 1;
-  d->marking_done = 1;
+  if (caml_gc_phase == Phase_sweep_main) {
+    d->sweeping_done = 1;
+    d->marking_done = 0;
+    atomic_fetch_add(&num_domains_to_mark, 1);
+    atomic_fetch_add(&ephe_cycle_info.num_domains_todo, 1);
+  } else {
+    d->sweeping_done = 1;
+    d->marking_done = 1;
+  }
+
   /* Finalisers. Fresh domains participate in updating finalisers. */
   d->final_info = caml_alloc_final_info ();
   if(d->final_info == NULL) {
diff --git a/ocaml/runtime/minor_gc.c b/ocaml/runtime/minor_gc.c
index 16a292f3c38..33177aa8206 100644
--- a/ocaml/runtime/minor_gc.c
+++ b/ocaml/runtime/minor_gc.c
@@ -829,8 +829,19 @@ int caml_do_opportunistic_major_slice
 
 /* Make sure the minor heap is empty by performing a minor collection
    if needed.
+
+   This function also samples [caml_gc_mark_phase_requested] to see whether
+   [caml_mark_roots_stw] should be called. To guarantee that all domains
+   agree on whether the roots should be marked, this variable is sampled
+   only once, instead of having domains check it individually.
 */
-void caml_empty_minor_heap_setup(caml_domain_state* domain_unused) {
+void caml_empty_minor_heap_setup(caml_domain_state* domain_unused,
+                                 void* mark_requested) {
+  /* Check whether the mark phase has been requested */
+  *((uintnat*)mark_requested) =
+    atomic_load_relaxed(&caml_gc_mark_phase_requested)
+    ? atomic_exchange(&caml_gc_mark_phase_requested, 0)
+    : 0;
   /* Increment the total number of minor collections done in the program */
   nonatomic_increment_counter (&caml_minor_collections_count);
   caml_plat_barrier_reset(&minor_gc_end_barrier);
@@ -839,7 +850,7 @@ void caml_empty_minor_heap_setup(caml_domain_state* domain_unused) {
 /* must be called within a STW section */
 static void
 caml_stw_empty_minor_heap_no_major_slice(caml_domain_state* domain,
-                                         void* unused,
+                                         void* mark_requested_ptr,
                                          int participating_count,
                                          caml_domain_state** participating)
 {
@@ -851,6 +862,9 @@ caml_stw_empty_minor_heap_no_major_slice(caml_domain_state* domain,
     caml_fatal_error("Minor GC triggered recursively");
   Caml_state->in_minor_collection = 1;
 
+  /* mark_requested_ptr must be read before minor GC barrier */
+  uintnat mark_requested = *(uintnat*)mark_requested_ptr;
+
   if( participating[0] == domain ) {
     nonatomic_increment_counter(&caml_minor_cycles_started);
   }
@@ -858,6 +872,10 @@ caml_stw_empty_minor_heap_no_major_slice(caml_domain_state* domain,
   caml_gc_log("running stw empty_minor_heap_promote");
   caml_empty_minor_heap_promote(domain, participating_count, participating);
 
+  /* while the minor heap is empty, allow the major GC to mark roots */
+  if (mark_requested)
+    caml_mark_roots_stw(participating_count, participating);
+
   CAML_EV_BEGIN(EV_MINOR_FINALIZED);
   caml_gc_log("finalizing dead minor custom blocks");
   custom_finalize_minor(domain);
@@ -887,11 +905,12 @@ caml_stw_empty_minor_heap_no_major_slice(caml_domain_state* domain,
   Caml_state->in_minor_collection = 0;
 }
 
-static void caml_stw_empty_minor_heap (caml_domain_state* domain, void* unused,
+static void caml_stw_empty_minor_heap (caml_domain_state* domain,
+                                       void* mark_requested,
                                        int participating_count,
                                        caml_domain_state** participating)
 {
-  caml_stw_empty_minor_heap_no_major_slice(domain, unused,
+  caml_stw_empty_minor_heap_no_major_slice(domain, mark_requested,
                                            participating_count, participating);
 }
 
@@ -902,13 +921,14 @@ void caml_empty_minor_heap_no_major_slice_from_stw(
   int participating_count,
   caml_domain_state** participating)
 {
+  static uintnat mark_requested; /* written by only one domain */
   Caml_global_barrier_if_final(participating_count) {
-    caml_empty_minor_heap_setup(domain);
+    caml_empty_minor_heap_setup(domain, &mark_requested);
   }
 
   /* if we are entering from within a major GC STW section then
      we do not schedule another major collection slice */
-  caml_stw_empty_minor_heap_no_major_slice(domain, (void*)0,
+  caml_stw_empty_minor_heap_no_major_slice(domain, &mark_requested,
                                            participating_count, participating);
 }
 
@@ -920,9 +940,11 @@ int caml_try_empty_minor_heap_on_all_domains (void)
   #endif
 
   caml_gc_log("requesting stw empty_minor_heap");
+  uintnat mark_requested;
   return caml_try_run_on_all_domains_with_spin_work(
     1, /* synchronous */
-    &caml_stw_empty_minor_heap, 0, /* stw handler */
+    &caml_stw_empty_minor_heap, /* stw handler */
+    &mark_requested,
     &caml_empty_minor_heap_setup, /* leader setup */
     &caml_do_opportunistic_major_slice, 0 /* enter spin work */);
     /* leaves when done by default*/
diff --git a/ocaml/runtime/signals.c b/ocaml/runtime/signals.c
index f505ff302c1..e466b218559 100644
--- a/ocaml/runtime/signals.c
+++ b/ocaml/runtime/signals.c
@@ -291,6 +291,9 @@ void caml_request_major_slice (int global)
   }else{
     Caml_state->requested_major_slice = 1;
   }
+  /* Beginning the mark phase requires emptying the minor heap */
+  if (atomic_load_relaxed(&caml_gc_mark_phase_requested))
+    Caml_state->requested_minor_gc = 1;
   caml_interrupt_self();
 }
 
diff --git a/ocaml/runtime/weak.c b/ocaml/runtime/weak.c
index 9b313c5b4ed..22c2a9d2910 100644
--- a/ocaml/runtime/weak.c
+++ b/ocaml/runtime/weak.c
@@ -59,16 +59,8 @@ CAMLprim value caml_ephe_create (value len)
     caml_invalid_argument ("Weak.create");
   res = caml_alloc_shr (size, Abstract_tag);
 
-  /* The new ephemeron needs to be added to:
-       live, if marking has started, to be marked next cycle
-       todo, if marking has not started, to be marked this cycle */
-  if (caml_marking_started()) {
-    Ephe_link(res) = domain_state->ephe_info->live;
-    domain_state->ephe_info->live = res;
-  } else {
-    Ephe_link(res) = domain_state->ephe_info->todo;
-    domain_state->ephe_info->todo = res;
-  }
+  Ephe_link(res) = domain_state->ephe_info->live;
+  domain_state->ephe_info->live = res;
   for (i = CAML_EPHE_DATA_OFFSET; i < size; i++)
     Field(res, i) = caml_ephe_none;
   /* run memprof callbacks */
diff --git a/ocaml/testsuite/tests/gc-roots/globroots_parallel.ml b/ocaml/testsuite/tests/gc-roots/globroots_parallel.ml
index 74f6808682c..71921d16fd8 100644
--- a/ocaml/testsuite/tests/gc-roots/globroots_parallel.ml
+++ b/ocaml/testsuite/tests/gc-roots/globroots_parallel.ml
@@ -1,8 +1,9 @@
 (* TEST
  flags += " -w a ";
  modules = "globrootsprim.c globroots.ml";
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 open Globroots
diff --git a/ocaml/testsuite/tests/gc-roots/globroots_parallel_spawn_burn.ml b/ocaml/testsuite/tests/gc-roots/globroots_parallel_spawn_burn.ml
index bdafc0da706..e72c81f10b0 100644
--- a/ocaml/testsuite/tests/gc-roots/globroots_parallel_spawn_burn.ml
+++ b/ocaml/testsuite/tests/gc-roots/globroots_parallel_spawn_burn.ml
@@ -1,8 +1,9 @@
 (* TEST
  flags += " -w a ";
  modules = "globrootsprim.c globroots.ml";
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 open Globroots
diff --git a/ocaml/testsuite/tests/lazy/lazy2.ml b/ocaml/testsuite/tests/lazy/lazy2.ml
index 478cf5acbe0..e7d7b408a7b 100644
--- a/ocaml/testsuite/tests/lazy/lazy2.ml
+++ b/ocaml/testsuite/tests/lazy/lazy2.ml
@@ -1,7 +1,8 @@
 (* TEST
  ocamlopt_flags += " -O3 ";
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 open Domain
diff --git a/ocaml/testsuite/tests/lazy/lazy3.ml b/ocaml/testsuite/tests/lazy/lazy3.ml
index 76843888e9e..a97265e84d3 100644
--- a/ocaml/testsuite/tests/lazy/lazy3.ml
+++ b/ocaml/testsuite/tests/lazy/lazy3.ml
@@ -1,7 +1,8 @@
 (* TEST
  ocamlopt_flags += " -O3 ";
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 let f count =
diff --git a/ocaml/testsuite/tests/lazy/lazy5.ml b/ocaml/testsuite/tests/lazy/lazy5.ml
index b220581ecc1..7545d7f5b67 100644
--- a/ocaml/testsuite/tests/lazy/lazy5.ml
+++ b/ocaml/testsuite/tests/lazy/lazy5.ml
@@ -1,7 +1,8 @@
 (* TEST
  ocamlopt_flags += " -O3 ";
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 let rec safe_force l =
   try Lazy.force l with
diff --git a/ocaml/testsuite/tests/lazy/lazy6.ml b/ocaml/testsuite/tests/lazy/lazy6.ml
index e07b60c3156..60a110348c2 100644
--- a/ocaml/testsuite/tests/lazy/lazy6.ml
+++ b/ocaml/testsuite/tests/lazy/lazy6.ml
@@ -1,7 +1,8 @@
 (* TEST
  ocamlopt_flags += " -O3 ";
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 let flag1 = Atomic.make false
diff --git a/ocaml/testsuite/tests/lazy/lazy7.ml b/ocaml/testsuite/tests/lazy/lazy7.ml
index d27aa248db7..37c23003b31 100644
--- a/ocaml/testsuite/tests/lazy/lazy7.ml
+++ b/ocaml/testsuite/tests/lazy/lazy7.ml
@@ -1,7 +1,8 @@
 (* TEST
  ocamlopt_flags += " -O3 ";
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 let num_domains = 4
diff --git a/ocaml/testsuite/tests/lazy/lazy8.ml b/ocaml/testsuite/tests/lazy/lazy8.ml
index 48c5bca29e7..a562a91ffaf 100644
--- a/ocaml/testsuite/tests/lazy/lazy8.ml
+++ b/ocaml/testsuite/tests/lazy/lazy8.ml
@@ -1,7 +1,8 @@
 (* TEST
  ocamlopt_flags += " -O3 ";
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 exception E
diff --git a/ocaml/testsuite/tests/lf_skiplist/test_parallel.ml b/ocaml/testsuite/tests/lf_skiplist/test_parallel.ml
index b218979d04f..45cb89f0df7 100644
--- a/ocaml/testsuite/tests/lf_skiplist/test_parallel.ml
+++ b/ocaml/testsuite/tests/lf_skiplist/test_parallel.ml
@@ -1,8 +1,9 @@
 (* TEST
  modules = "stubs.c";
- no-tsan; (* Takes too much time and memory with tsan *)
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ no-tsan;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 external init_skiplist : unit -> unit = "init_skiplist"
diff --git a/ocaml/testsuite/tests/lib-channels/refcounting.ml b/ocaml/testsuite/tests/lib-channels/refcounting.ml
index 84776f440b4..b80a7bb64be 100644
--- a/ocaml/testsuite/tests/lib-channels/refcounting.ml
+++ b/ocaml/testsuite/tests/lib-channels/refcounting.ml
@@ -1,6 +1,5 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
  expect;
 *)
 
diff --git a/ocaml/testsuite/tests/lib-dynlink-domains/main.ml b/ocaml/testsuite/tests/lib-dynlink-domains/main.ml
index e5666c8897e..b7e83c64e4c 100644
--- a/ocaml/testsuite/tests/lib-dynlink-domains/main.ml
+++ b/ocaml/testsuite/tests/lib-dynlink-domains/main.ml
@@ -1,10 +1,5 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
-*)
-
-(* BACKPORT
-(* TEST
+ runtime5;
  include dynlink;
  libraries = "";
  readonly_files = "store.ml main.ml Plugin_0.ml Plugin_0_0.ml Plugin_0_0_0.ml Plugin_0_0_0_0.ml Plugin_0_0_0_1.ml Plugin_0_0_0_2.ml Plugin_1.ml Plugin_1_0.ml Plugin_1_0_0.ml Plugin_1_0_0_0.ml Plugin_1_1.ml Plugin_1_2.ml Plugin_1_2_0.ml Plugin_1_2_0_0.ml Plugin_1_2_1.ml Plugin_1_2_2.ml Plugin_1_2_2_0.ml Plugin_1_2_3.ml Plugin_1_2_3_0.ml";
@@ -228,5 +223,3 @@ let stored = Atomic.get Store.store
 let stored_set = String_set.of_list stored
 let () =
   List.iter (Printf.printf "%s\n") (String_set.elements stored_set)
-
-*)
diff --git a/ocaml/testsuite/tests/lib-format/domains.ml b/ocaml/testsuite/tests/lib-format/domains.ml
index 4bfaa594124..896675f5ac3 100644
--- a/ocaml/testsuite/tests/lib-format/domains.ml
+++ b/ocaml/testsuite/tests/lib-format/domains.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 (** Test that domains stdout and stderr are flushed at domain exit *)
diff --git a/ocaml/testsuite/tests/lib-format/mc_pr586_par.ml b/ocaml/testsuite/tests/lib-format/mc_pr586_par.ml
index c8475c37a38..87b1d2f8210 100644
--- a/ocaml/testsuite/tests/lib-format/mc_pr586_par.ml
+++ b/ocaml/testsuite/tests/lib-format/mc_pr586_par.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 let () =
diff --git a/ocaml/testsuite/tests/lib-format/mc_pr586_par2.ml b/ocaml/testsuite/tests/lib-format/mc_pr586_par2.ml
index d2dd7b06a69..23bb3e9bb34 100644
--- a/ocaml/testsuite/tests/lib-format/mc_pr586_par2.ml
+++ b/ocaml/testsuite/tests/lib-format/mc_pr586_par2.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 let () =
diff --git a/ocaml/testsuite/tests/lib-marshal/intext_par.ml b/ocaml/testsuite/tests/lib-marshal/intext_par.ml
index e505f82914c..93bec50489b 100644
--- a/ocaml/testsuite/tests/lib-marshal/intext_par.ml
+++ b/ocaml/testsuite/tests/lib-marshal/intext_par.ml
@@ -1,8 +1,9 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
  modules = "intextaux_par.c";
- no-tsan; (* Takes too much time and memory with tsan *)
- skip;
+ no-tsan;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 (* Test for output_value / input_value *)
diff --git a/ocaml/testsuite/tests/lib-random/parallel.ml b/ocaml/testsuite/tests/lib-random/parallel.ml
index 07805a0e878..a58bfa7c159 100644
--- a/ocaml/testsuite/tests/lib-random/parallel.ml
+++ b/ocaml/testsuite/tests/lib-random/parallel.ml
@@ -1,7 +1,6 @@
 (* TEST
  include unix;
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
  libunix;
  {
    bytecode;
diff --git a/ocaml/testsuite/tests/lib-str/parallel.ml b/ocaml/testsuite/tests/lib-str/parallel.ml
index 1d9f2f5d388..4c4926ca3ea 100644
--- a/ocaml/testsuite/tests/lib-str/parallel.ml
+++ b/ocaml/testsuite/tests/lib-str/parallel.ml
@@ -1,6 +1,5 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
  include str;
  hasstr;
  {
diff --git a/ocaml/testsuite/tests/lib-sync/prodcons.ml b/ocaml/testsuite/tests/lib-sync/prodcons.ml
index f02257b7547..19f5e1607a8 100644
--- a/ocaml/testsuite/tests/lib-sync/prodcons.ml
+++ b/ocaml/testsuite/tests/lib-sync/prodcons.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 (* Classic producer-consumer *)
diff --git a/ocaml/testsuite/tests/lib-systhreads/multicore_lifecycle.ml b/ocaml/testsuite/tests/lib-systhreads/multicore_lifecycle.ml
index 018b8548e5d..f1ea4dd0f1d 100644
--- a/ocaml/testsuite/tests/lib-systhreads/multicore_lifecycle.ml
+++ b/ocaml/testsuite/tests/lib-systhreads/multicore_lifecycle.ml
@@ -1,8 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
  include systhreads;
  hassysthreads;
+ runtime5;
  {
    bytecode;
  }{
diff --git a/ocaml/testsuite/tests/lib-unix/common/multicore_fork_domain_alone.ml b/ocaml/testsuite/tests/lib-unix/common/multicore_fork_domain_alone.ml
index 66ccfc2dd8a..99c10547702 100644
--- a/ocaml/testsuite/tests/lib-unix/common/multicore_fork_domain_alone.ml
+++ b/ocaml/testsuite/tests/lib-unix/common/multicore_fork_domain_alone.ml
@@ -1,7 +1,6 @@
 (* TEST
+ runtime5;
  include unix;
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
  hasunix;
  not-windows;
  {
diff --git a/ocaml/testsuite/tests/lib-unix/common/multicore_fork_domain_alone2.ml b/ocaml/testsuite/tests/lib-unix/common/multicore_fork_domain_alone2.ml
index c3751f2b949..c87e8006f2b 100644
--- a/ocaml/testsuite/tests/lib-unix/common/multicore_fork_domain_alone2.ml
+++ b/ocaml/testsuite/tests/lib-unix/common/multicore_fork_domain_alone2.ml
@@ -1,7 +1,6 @@
 (* TEST
+ runtime5;
  include unix;
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
  hasunix;
  not-windows;
  {
diff --git a/ocaml/testsuite/tests/memory-model/forbidden.ml b/ocaml/testsuite/tests/memory-model/forbidden.ml
index fd97ce536ce..9b9a59274dc 100644
--- a/ocaml/testsuite/tests/memory-model/forbidden.ml
+++ b/ocaml/testsuite/tests/memory-model/forbidden.ml
@@ -1,9 +1,8 @@
 (* TEST
  modules = "opt.ml barrier.ml hist.ml shared.ml run.ml outcome.ml";
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
  not-bsd;
  no-tsan; (* tsan detects the intentional data races and fails *)
+ runtime5;
  {
    bytecode;
  }{
diff --git a/ocaml/testsuite/tests/memory-model/publish.ml b/ocaml/testsuite/tests/memory-model/publish.ml
index da486ce5b3f..f7b4b7539d8 100644
--- a/ocaml/testsuite/tests/memory-model/publish.ml
+++ b/ocaml/testsuite/tests/memory-model/publish.ml
@@ -1,9 +1,8 @@
 (* TEST
  modules = "opt.ml barrier.ml hist.ml shared.ml run.ml outcome.ml";
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
  not-bsd;
  no-tsan; (* tsan detects data races and fails *)
+ runtime5;
  {
    not-windows;
    bytecode;
diff --git a/ocaml/testsuite/tests/parallel/atomics.ml b/ocaml/testsuite/tests/parallel/atomics.ml
index 6f092ca6233..e0ace87a100 100644
--- a/ocaml/testsuite/tests/parallel/atomics.ml
+++ b/ocaml/testsuite/tests/parallel/atomics.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 type u = U of unit
diff --git a/ocaml/testsuite/tests/parallel/backup_thread.ml b/ocaml/testsuite/tests/parallel/backup_thread.ml
index d3d3a19581b..7b0e4525368 100644
--- a/ocaml/testsuite/tests/parallel/backup_thread.ml
+++ b/ocaml/testsuite/tests/parallel/backup_thread.ml
@@ -1,6 +1,5 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
  include unix;
  hasunix;
  {
diff --git a/ocaml/testsuite/tests/parallel/backup_thread_pipe.ml b/ocaml/testsuite/tests/parallel/backup_thread_pipe.ml
index e063b4843fb..c558ba0a854 100644
--- a/ocaml/testsuite/tests/parallel/backup_thread_pipe.ml
+++ b/ocaml/testsuite/tests/parallel/backup_thread_pipe.ml
@@ -1,6 +1,5 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
  include unix;
  hasunix;
  {
diff --git a/ocaml/testsuite/tests/parallel/catch_break.ml b/ocaml/testsuite/tests/parallel/catch_break.ml
index 0b6c4d9fa22..8176a50684d 100644
--- a/ocaml/testsuite/tests/parallel/catch_break.ml
+++ b/ocaml/testsuite/tests/parallel/catch_break.ml
@@ -1,13 +1,10 @@
 (* TEST
-reason = "CR ocaml 5 domains: re-enable this test";
-skip;
-*)
-
-(*
 hassysthreads;
 include systhreads;
 not-windows;
+poll-insertion;
 no-tsan;
+runtime5;
 {
   bytecode;
 }{
@@ -79,7 +76,7 @@ let rec wait n =
    callback implementation than we want.*)
 let break_trap s =
   begin
-    try Atomic.incr ready_count; while true do () done
+    try Sys.with_async_exns (fun () -> Atomic.incr ready_count; while true do () done)
     with Sys.Break -> print "[Sys.Break caught]"
   end;
   print s;
@@ -112,7 +109,7 @@ let run () =
 
 let () =
   Sys.catch_break true;
-  (try run () with Sys.Break ->
+  (try Sys.with_async_exns run with Sys.Break ->
      print ("Test could not complete due to scheduling hazard"
             ^ " (possible false positive)."));
   print "Success.";
diff --git a/ocaml/testsuite/tests/parallel/churn.ml b/ocaml/testsuite/tests/parallel/churn.ml
new file mode 100644
index 00000000000..1472b216e5f
--- /dev/null
+++ b/ocaml/testsuite/tests/parallel/churn.ml
@@ -0,0 +1,69 @@
+(* TEST
+ runtime5;
+ { bytecode; }
+ { native; }
+*)
+
+type t = {
+  sender: int;
+  code: int;
+  msgsize: int;
+  message: int array;
+}
+
+let size = 20_000
+let table = Array.init size (fun _ -> Atomic.make None)
+let go = Atomic.make true
+let log = false
+
+let run me msgsize iters =
+  (* domain 0 keeps a bunch of extra local data,
+     to unbalance sweeping loads *)
+  let kept = ref [] in
+  if me = 0 then kept := [Array.init 10000 ref];
+  let count = ref iters in
+  let from0 = ref 0 in
+  while !count > 0 && Atomic.get go do
+    ignore (Sys.opaque_identity (ref []));
+    let slot = Random.int size in
+    match Atomic.get table.(slot) with
+    | None as prev ->
+      let code = Random.bits () in
+      let msg = {sender = me; code; msgsize; message = Array.make msgsize code} in
+      if me = 0 then kept := Array.init 5 ref :: !kept;
+      (* pointless string formatting to create minor garbage *)
+      let dbg =
+        Printf.sprintf "[%d]:      %03d: %d %08x --->\n" me slot msg.msgsize msg.code in
+      if Sys.opaque_identity log then print_string dbg;
+      if Atomic.compare_and_set table.(slot) prev (Some msg) then
+        decr count
+    | Some msg as prev when
+        msg.sender <> me &&
+        Atomic.compare_and_set table.(slot) prev None ->
+
+      let dbg = Printf.sprintf "[%d]: ---> %03d: %d %08x\n" me slot msg.msgsize msg.code in
+      if Sys.opaque_identity log then print_string dbg;
+      assert (Array.length msg.message = msg.msgsize);
+      for i = 0 to msg.msgsize - 1 do
+        assert (msg.message.(i) = msg.code)
+      done;
+      if msg.sender = 0 then incr from0;
+    | Some _ -> ()
+  done;
+  ignore (Sys.opaque_identity !kept);
+  !from0
+
+let () =
+  let iters = 200_000 in
+  let d1 = Domain.spawn (fun () -> run 1 100 max_int) in
+  let d2 = Domain.spawn (fun () -> run 2 5 max_int) in
+  let recv_local = run 0 20 iters in
+  assert (recv_local = 0);
+  Atomic.set go false;
+  let r = Domain.join d1 + Domain.join d2 in
+  let remaining =
+    table
+    |> Array.to_list
+    |> List.filter (fun x -> match Atomic.get x with Some {sender=0; _} -> true | _ -> false)
+    |> List.length in
+  Printf.printf "%d\n" (r+remaining)
diff --git a/ocaml/testsuite/tests/parallel/churn.reference b/ocaml/testsuite/tests/parallel/churn.reference
new file mode 100644
index 00000000000..87766d889a3
--- /dev/null
+++ b/ocaml/testsuite/tests/parallel/churn.reference
@@ -0,0 +1 @@
+200000
diff --git a/ocaml/testsuite/tests/parallel/constpromote.ml b/ocaml/testsuite/tests/parallel/constpromote.ml
index c8a0e6b2565..6e76b106aa5 100644
--- a/ocaml/testsuite/tests/parallel/constpromote.ml
+++ b/ocaml/testsuite/tests/parallel/constpromote.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 (* when run with the bytecode debug runtime, this test
diff --git a/ocaml/testsuite/tests/parallel/deadcont.ml b/ocaml/testsuite/tests/parallel/deadcont.ml
index d4180fe4a36..f3726e263d1 100644
--- a/ocaml/testsuite/tests/parallel/deadcont.ml
+++ b/ocaml/testsuite/tests/parallel/deadcont.ml
@@ -1,6 +1,8 @@
 (* TEST
- reason = "CR ocaml 5 effects: re-enable this test";
  skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 (*
diff --git a/ocaml/testsuite/tests/parallel/domain_dls.ml b/ocaml/testsuite/tests/parallel/domain_dls.ml
index c9c6629b8fc..77ca1b71650 100644
--- a/ocaml/testsuite/tests/parallel/domain_dls.ml
+++ b/ocaml/testsuite/tests/parallel/domain_dls.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 let check_dls () =
diff --git a/ocaml/testsuite/tests/parallel/domain_dls2.ml b/ocaml/testsuite/tests/parallel/domain_dls2.ml
index 97a8c6aff44..fde7279024b 100644
--- a/ocaml/testsuite/tests/parallel/domain_dls2.ml
+++ b/ocaml/testsuite/tests/parallel/domain_dls2.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 let _ =
diff --git a/ocaml/testsuite/tests/parallel/domain_id.ml b/ocaml/testsuite/tests/parallel/domain_id.ml
index 47cd6ccbe4a..f48fca37bfe 100644
--- a/ocaml/testsuite/tests/parallel/domain_id.ml
+++ b/ocaml/testsuite/tests/parallel/domain_id.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 open Domain
diff --git a/ocaml/testsuite/tests/parallel/domain_parallel_spawn_burn.ml b/ocaml/testsuite/tests/parallel/domain_parallel_spawn_burn.ml
index 16fe1279bc9..b3d2517848b 100644
--- a/ocaml/testsuite/tests/parallel/domain_parallel_spawn_burn.ml
+++ b/ocaml/testsuite/tests/parallel/domain_parallel_spawn_burn.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 open Domain
diff --git a/ocaml/testsuite/tests/parallel/domain_parallel_spawn_burn_gc_set.ml b/ocaml/testsuite/tests/parallel/domain_parallel_spawn_burn_gc_set.ml
index d07187de741..bc33818b2de 100644
--- a/ocaml/testsuite/tests/parallel/domain_parallel_spawn_burn_gc_set.ml
+++ b/ocaml/testsuite/tests/parallel/domain_parallel_spawn_burn_gc_set.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 open Domain
diff --git a/ocaml/testsuite/tests/parallel/domain_serial_spawn_burn.ml b/ocaml/testsuite/tests/parallel/domain_serial_spawn_burn.ml
index c51ec2e16cd..c1b4b28f7b3 100644
--- a/ocaml/testsuite/tests/parallel/domain_serial_spawn_burn.ml
+++ b/ocaml/testsuite/tests/parallel/domain_serial_spawn_burn.ml
@@ -1,6 +1,5 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
  include unix;
  hasunix;
  {
diff --git a/ocaml/testsuite/tests/parallel/fib_threads.ml b/ocaml/testsuite/tests/parallel/fib_threads.ml
index b6f68ca3c40..4a4c33d2ae0 100644
--- a/ocaml/testsuite/tests/parallel/fib_threads.ml
+++ b/ocaml/testsuite/tests/parallel/fib_threads.ml
@@ -1,6 +1,5 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
  include systhreads;
  hassysthreads;
  {
diff --git a/ocaml/testsuite/tests/parallel/join.ml b/ocaml/testsuite/tests/parallel/join.ml
index b42f613f253..5db4fc77fca 100644
--- a/ocaml/testsuite/tests/parallel/join.ml
+++ b/ocaml/testsuite/tests/parallel/join.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 let test_size =
diff --git a/ocaml/testsuite/tests/parallel/major_gc_wait_backup.ml b/ocaml/testsuite/tests/parallel/major_gc_wait_backup.ml
index 2f39b4d5441..6941ca7f731 100644
--- a/ocaml/testsuite/tests/parallel/major_gc_wait_backup.ml
+++ b/ocaml/testsuite/tests/parallel/major_gc_wait_backup.ml
@@ -1,6 +1,5 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
  include unix;
  hasunix;
  {
diff --git a/ocaml/testsuite/tests/parallel/mctest.ml b/ocaml/testsuite/tests/parallel/mctest.ml
index e6be5b08a64..985bd647de5 100644
--- a/ocaml/testsuite/tests/parallel/mctest.ml
+++ b/ocaml/testsuite/tests/parallel/mctest.ml
@@ -1,6 +1,6 @@
 (* TEST
- reason = "CR ocaml 5 effects: re-enable this test";
  skip;
+ runtime5;
  include unix;
  hasunix;
  {
diff --git a/ocaml/testsuite/tests/parallel/multicore_systhreads.ml b/ocaml/testsuite/tests/parallel/multicore_systhreads.ml
index ddc82a7356f..b100efa879c 100644
--- a/ocaml/testsuite/tests/parallel/multicore_systhreads.ml
+++ b/ocaml/testsuite/tests/parallel/multicore_systhreads.ml
@@ -1,6 +1,5 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
  include systhreads;
  hassysthreads;
  {
diff --git a/ocaml/testsuite/tests/parallel/pingpong.ml b/ocaml/testsuite/tests/parallel/pingpong.ml
index a38d6bab555..2074b9eac43 100644
--- a/ocaml/testsuite/tests/parallel/pingpong.ml
+++ b/ocaml/testsuite/tests/parallel/pingpong.ml
@@ -1,13 +1,8 @@
 (* TEST
  no-tsan; (* TSan detects the intentional data race *)
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
- {
-   bytecode;
- }
- {
-   native;
- }
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 let r = ref (Some 0)
diff --git a/ocaml/testsuite/tests/parallel/poll.ml b/ocaml/testsuite/tests/parallel/poll.ml
index a2a219f2f9b..087790b1f2c 100644
--- a/ocaml/testsuite/tests/parallel/poll.ml
+++ b/ocaml/testsuite/tests/parallel/poll.ml
@@ -1,8 +1,8 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ poll-insertion;
  include unix;
  hasunix;
+ runtime5;
  {
    bytecode;
  }{
diff --git a/ocaml/testsuite/tests/parallel/prodcons_domains.ml b/ocaml/testsuite/tests/parallel/prodcons_domains.ml
index f02257b7547..19f5e1607a8 100644
--- a/ocaml/testsuite/tests/parallel/prodcons_domains.ml
+++ b/ocaml/testsuite/tests/parallel/prodcons_domains.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 (* Classic producer-consumer *)
diff --git a/ocaml/testsuite/tests/parallel/recommended_domain_count.ml b/ocaml/testsuite/tests/parallel/recommended_domain_count.ml
index 3e04ea9ebff..79358b243c5 100644
--- a/ocaml/testsuite/tests/parallel/recommended_domain_count.ml
+++ b/ocaml/testsuite/tests/parallel/recommended_domain_count.ml
@@ -1,7 +1,8 @@
 (* TEST
  modules = "recommended_domain_count_cstubs.c";
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 external get_max_domains : unit -> int = "caml_get_max_domains"
diff --git a/ocaml/testsuite/tests/parallel/recommended_domain_count_unix.ml b/ocaml/testsuite/tests/parallel/recommended_domain_count_unix.ml
index eea7672d925..c76da9cef15 100644
--- a/ocaml/testsuite/tests/parallel/recommended_domain_count_unix.ml
+++ b/ocaml/testsuite/tests/parallel/recommended_domain_count_unix.ml
@@ -1,6 +1,5 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
  include unix;
  hasunix;
  {
diff --git a/ocaml/testsuite/tests/parallel/tak.ml b/ocaml/testsuite/tests/parallel/tak.ml
index ce81c1e8a10..2821fbb1146 100644
--- a/ocaml/testsuite/tests/parallel/tak.ml
+++ b/ocaml/testsuite/tests/parallel/tak.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 (* filling minor heaps in parallel to trigger
diff --git a/ocaml/testsuite/tests/parallel/test_c_thread_register.ml b/ocaml/testsuite/tests/parallel/test_c_thread_register.ml
index 5e888c8b4c9..616053640bd 100644
--- a/ocaml/testsuite/tests/parallel/test_c_thread_register.ml
+++ b/ocaml/testsuite/tests/parallel/test_c_thread_register.ml
@@ -1,7 +1,6 @@
 (* TEST
  modules = "test_c_thread_register_cstubs.c";
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
  include systhreads;
  hassysthreads;
  {
diff --git a/ocaml/testsuite/tests/parallel/test_issue_11094.ml b/ocaml/testsuite/tests/parallel/test_issue_11094.ml
index 12060d1d837..98cacc15ab3 100644
--- a/ocaml/testsuite/tests/parallel/test_issue_11094.ml
+++ b/ocaml/testsuite/tests/parallel/test_issue_11094.ml
@@ -1,6 +1,7 @@
 (* TEST
  reason = "CR ocaml 5 effects: re-enable this test";
  skip;
+ runtime5;
  {
    bytecode;
  }{
diff --git a/ocaml/testsuite/tests/weak-ephe-final/ephetest_par.ml b/ocaml/testsuite/tests/weak-ephe-final/ephetest_par.ml
index 2eff91f62d8..f30b7b5bacd 100644
--- a/ocaml/testsuite/tests/weak-ephe-final/ephetest_par.ml
+++ b/ocaml/testsuite/tests/weak-ephe-final/ephetest_par.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 (* Due to GCs running at non-deterministic places, the output from these tests
diff --git a/ocaml/testsuite/tests/weak-ephe-final/finaliser2.ml b/ocaml/testsuite/tests/weak-ephe-final/finaliser2.ml
index 4a4dc3e0fa8..e10f4906239 100644
--- a/ocaml/testsuite/tests/weak-ephe-final/finaliser2.ml
+++ b/ocaml/testsuite/tests/weak-ephe-final/finaliser2.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 let () = Out_channel.set_buffered stdout false
diff --git a/ocaml/testsuite/tests/weak-ephe-final/finaliser_handover.ml b/ocaml/testsuite/tests/weak-ephe-final/finaliser_handover.ml
index 7f97a43ddf5..5d487ae62cd 100644
--- a/ocaml/testsuite/tests/weak-ephe-final/finaliser_handover.ml
+++ b/ocaml/testsuite/tests/weak-ephe-final/finaliser_handover.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 (* ocaml-multicore issues 528 and 468 *)
diff --git a/ocaml/testsuite/tests/weak-ephe-final/weaktest_par_load.ml b/ocaml/testsuite/tests/weak-ephe-final/weaktest_par_load.ml
index eb39ff9f1fb..59ef21620bb 100644
--- a/ocaml/testsuite/tests/weak-ephe-final/weaktest_par_load.ml
+++ b/ocaml/testsuite/tests/weak-ephe-final/weaktest_par_load.ml
@@ -1,6 +1,7 @@
 (* TEST
- reason = "CR ocaml 5 domains: re-enable this test";
- skip;
+ runtime5;
+ { bytecode; }
+ { native; }
 *)
 
 (* Testing unsynchronized, parallel Weak usage *)