erts: Remove ets traversal yielding if heap fragment

Many heap fragments do no longer make the GC slow.

Even worse, we are not guaranteed that a yield will provoke a GC
removing the fragments, which might lead to a one-yield-per-bucket
scenario if the heap fragment(s) still remains after each yield.

4 files changed, 69 insertions, 25 deletions

diff --git a/erts/emulator/beam/erl_bif_info.c b/erts/emulator/beam/erl_bif_info.c
index 4050fb6146..43d99db0b2 100644
--- a/erts/emulator/beam/erl_bif_info.c
+++ b/erts/emulator/beam/erl_bif_info.c
@@ -4459,7 +4459,16 @@ BIF_RETTYPE erts_debug_set_internal_state_2(BIF_ALIST_2)
                                             refbin));
             }
         }
-
+        else if (ERTS_IS_ATOM_STR("mbuf", BIF_ARG_1)) {
+            Uint sz = size_object(BIF_ARG_2);
+            ErlHeapFragment* frag = new_message_buffer(sz);
+            Eterm *hp = frag->mem;
+            Eterm copy = copy_struct(BIF_ARG_2, sz, &hp, &frag->off_heap);
+            frag->next = BIF_P->mbuf;
+            BIF_P->mbuf = frag;
+            BIF_P->mbuf_sz += sz;
+            BIF_RET(copy);
+        }
     }
 
     BIF_ERROR(BIF_P, BADARG);
diff --git a/erts/emulator/beam/erl_db_hash.c b/erts/emulator/beam/erl_db_hash.c
index cf928a9035..47d304f860 100644
--- a/erts/emulator/beam/erl_db_hash.c
+++ b/erts/emulator/beam/erl_db_hash.c
@@ -1328,11 +1328,7 @@ static int match_traverse(Process* p, DbTableHash* tb,
                 unlock_hash_function(lck);
                 break;
             }
-            if (iterations_left <= 0 || MBUF(p)) {
-                /*
-                 * We have either reached our limit, or just created some heap fragments.
-                 * Since many heap fragments will make the GC slower, trap and GC now.
-                 */
+            if (iterations_left <= 0) {
                 unlock_hash_function(lck);
                 ret_value = on_trap(context_ptr, slot_ix, got, &mpi.mp, ret);
                 goto done;
@@ -1451,11 +1447,7 @@ static int match_traverse_continue(Process* p, DbTableHash* tb,
                 unlock_hash_function(lck);
                 break;
             }
-            if (iterations_left <= 0 || MBUF(p)) {
-                /*
-                 * We have either reached our limit, or just created some heap fragments.
-                 * Since many heap fragments will make the GC slower, trap and GC now.
-                 */
+            if (iterations_left <= 0) {
                 unlock_hash_function(lck);
                 ret_value = on_trap(context_ptr, slot_ix, got, mpp, ret);
                 goto done;
diff --git a/erts/emulator/beam/erl_db_tree.c b/erts/emulator/beam/erl_db_tree.c
index 7c80e92e50..f222ac45ae 100644
--- a/erts/emulator/beam/erl_db_tree.c
+++ b/erts/emulator/beam/erl_db_tree.c
@@ -3344,13 +3344,6 @@ static int doit_select(DbTableTree *tb, TreeDbTerm *this, void *ptr,
     if (is_value(ret)) {
 	sc->accum = CONS(hp, ret, sc->accum);
     }
-    if (MBUF(sc->p)) {
-	/*
-	 * Force a trap and GC if a heap fragment was created. Many heap fragments
-	 * make the GC slow.
-	 */
-	sc->max = 0;
-    }
     if (--(sc->max) <= 0) {
 	return 0;
     }
@@ -3407,13 +3400,6 @@ static int doit_select_chunk(DbTableTree *tb, TreeDbTerm *this, void *ptr,
 	++(sc->got);
 	sc->accum = CONS(hp, ret, sc->accum);
     }
-    if (MBUF(sc->p)) {
-	/*
-	 * Force a trap and GC if a heap fragment was created. Many heap fragments
-	 * make the GC slow.
-	 */
-	sc->max = 0;
-    }
     if (--(sc->max) <= 0 || sc->got == sc->chunk_size) {
 	return 0;
     }
diff --git a/lib/stdlib/test/ets_SUITE.erl b/lib/stdlib/test/ets_SUITE.erl
index 1a8260b041..bbbbab2f60 100644
--- a/lib/stdlib/test/ets_SUITE.erl
+++ b/lib/stdlib/test/ets_SUITE.erl
@@ -58,6 +58,7 @@
 -export([otp_5340/1]).
 -export([otp_6338/1]).
 -export([otp_6842_select_1000/1]).
+-export([select_mbuf_trapping/1]).
 -export([otp_7665/1]).
 -export([meta_wb/1]).
 -export([grow_shrink/1, grow_pseudo_deleted/1, shrink_pseudo_deleted/1]).
@@ -125,6 +126,7 @@ all() ->
      t_ets_dets, memory, t_select_reverse, t_bucket_disappears,
      select_fail, t_insert_new, t_repair_continuation,
      otp_5340, otp_6338, otp_6842_select_1000, otp_7665,
+     select_mbuf_trapping,
      otp_8732, meta_wb, grow_shrink, grow_pseudo_deleted,
      shrink_pseudo_deleted, {group, meta_smp}, smp_insert,
      smp_fixed_delete, smp_unfix_fix, smp_select_replace, 
@@ -5022,6 +5024,61 @@ otp_6338(Config) when is_list(Config) ->
     [[4839,recv]] = ets:match(T,{[{sbm,ppb2_bs12@blade_0_8},'$1'],'$2'}),
     ets:delete(T).
 
+%% OTP-15660: Verify select not doing excessive trapping
+%%            when process have mbuf heap fragments.
+select_mbuf_trapping(Config) when is_list(Config) ->
+    select_mbuf_trapping_do(set),
+    select_mbuf_trapping_do(ordered_set).
+
+select_mbuf_trapping_do(Type) ->
+    T = ets:new(xxx, [Type]),
+    NKeys = 50,
+    [ets:insert(T, {K, value}) || K <- lists:seq(1,NKeys)],
+
+    {priority, Prio} = process_info(self(), priority),
+    Tracee = self(),
+    [SchedTracer]
+	= start_loopers(1, Prio,
+			fun (SC) ->
+				receive
+				    {trace, Tracee, out, _} ->
+					SC+1;
+				    done ->
+					Tracee ! {schedule_count, SC},
+                                        exit(normal)
+				end
+			end,
+			0),
+
+    erlang:garbage_collect(),
+    1 = erlang:trace(self(), true, [running,{tracer,SchedTracer}]),
+
+    %% Artificially create an mbuf heap fragment
+    MbufTerm = "Frag me up",
+    MbufTerm = erts_debug:set_internal_state(mbuf, MbufTerm),
+
+    Keys = ets:select(T, [{{'$1', value}, [], ['$1']}]),
+    NKeys = length(Keys),
+
+    1 = erlang:trace(self(), false, [running]),
+    Ref = erlang:trace_delivered(Tracee),
+    receive
+        {trace_delivered, Tracee, Ref} ->
+            SchedTracer ! done
+    end,
+    receive
+	{schedule_count, N} ->
+	    io:format("~p context switches: ~p", [Type,N]),
+	    if
+		N < 3 -> ok;
+		true -> ct:fail(failed)
+	    end
+    end,
+    true = ets:delete(T),
+    ok.
+
+
+
 %% Elements could come in the wrong order in a bag if a rehash occurred.
 otp_5340(Config) when is_list(Config) ->
     repeat_for_opts(fun otp_5340_do/1).