From 3ac08f9b668613a4292436979eacc61863c2ab94 Mon Sep 17 00:00:00 2001
From: Rickard Green <rickard@erlang.org>
Date: Wed, 16 Sep 2015 15:02:50 +0200
Subject: Fragmented young heap generation and off_heap_message_queue option

* The youngest generation of the heap can now consist of multiple
  blocks. Heap fragments and message fragments are added to the
  youngest generation when needed without triggering a GC. After
  a GC the youngest generation is contained in one single block.
* The off_heap_message_queue process flag has been added. When
  enabled all message data in the queue is kept off heap. When
  a message is selected from the queue, the message fragment (or
  heap fragment) containing the actual message is attached to the
  youngest generation. Messages stored off heap is not part of GC.
---
 erts/emulator/beam/erl_hl_timer.c | 85 +++++++++++++++++----------------------
 1 file changed, 36 insertions(+), 49 deletions(-)

(limited to 'erts/emulator/beam/erl_hl_timer.c')

diff --git a/erts/emulator/beam/erl_hl_timer.c b/erts/emulator/beam/erl_hl_timer.c
index 51a0d68247..6853278828 100644
--- a/erts/emulator/beam/erl_hl_timer.c
+++ b/erts/emulator/beam/erl_hl_timer.c
@@ -1245,7 +1245,9 @@ hlt_bif_timer_timeout(ErtsHLTimer *tmr, Uint32 roflgs)
 	 * the middle of tree destruction).
 	 */
 	if (!ERTS_PROC_IS_EXITING(proc)) {
-	    erts_queue_message(proc, &proc_locks, tmr->btm.bp,
+	    ErtsMessage *mp = erts_alloc_message(0, NULL);
+	    mp->data.heap_frag = tmr->btm.bp;
+	    erts_queue_message(proc, &proc_locks, mp,
 			       tmr->btm.message, NIL);
 	    erts_smp_proc_unlock(proc, ERTS_PROC_LOCKS_MSG_SEND);
 	    queued_message = 1;
@@ -1926,36 +1928,31 @@ access_sched_local_btm(Process *c_p, Eterm pid,
 
     if (proc) {
 	Uint hsz;
-	ErlOffHeap *ohp;
-	ErlHeapFragment* bp;
+	ErtsMessage *mp;
 	Eterm *hp, msg, ref, result;
+	ErlOffHeap *ohp;
+	Uint32 *refn;
 #ifdef ERTS_HLT_DEBUG
 	Eterm *hp_end;
 #endif
 
-	hsz = 3; /* 2-tuple */
-	if (!async)
-	    hsz += REF_THING_SIZE;
+	hsz = REF_THING_SIZE;
+	if (async) {
+	    refn = trefn; /* timer ref */
+	    hsz += 4; /* 3-tuple */
+	}
 	else {
-	    if (is_non_value(tref) || proc != c_p)
-		hsz += REF_THING_SIZE;
-	    hsz += 1; /* upgrade to 3-tuple */
+	    refn = rrefn; /* request ref */
+	    hsz += 3; /* 2-tuple */
 	}
+
+	ERTS_HLT_ASSERT(refn);
+
 	if (time_left > (Sint64) MAX_SMALL)
 	    hsz += ERTS_SINT64_HEAP_SIZE(time_left);
 
-	if (proc == c_p) {
-	    bp = NULL;
-	    ohp = NULL;
-	    hp = HAlloc(c_p, hsz);
-	}
-	else {
-	    hp = erts_alloc_message_heap(hsz,
-					 &bp,
-					 &ohp,
-					 proc,
-					 &proc_locks);
-	}
+	mp = erts_alloc_message_heap(proc, &proc_locks,
+				     hsz, &hp, &ohp);
 
 #ifdef ERTS_HLT_DEBUG
 	hp_end = hp + hsz;
@@ -1968,35 +1965,22 @@ access_sched_local_btm(Process *c_p, Eterm pid,
 	else
 	    result = erts_sint64_to_big(time_left, &hp);
 
-	if (!async) {
-	    write_ref_thing(hp,
-			    rrefn[0],
-			    rrefn[1],
-			    rrefn[2]);
-	    ref = make_internal_ref(hp);
-	    hp += REF_THING_SIZE;
-	    msg = TUPLE2(hp, ref, result);
+	write_ref_thing(hp,
+			refn[0],
+			refn[1],
+			refn[2]);
+	ref = make_internal_ref(hp);
+	hp += REF_THING_SIZE;
 
-	    ERTS_HLT_ASSERT(hp + 3 == hp_end);
-	}
-	else {
-	    Eterm tag = cancel ? am_cancel_timer : am_read_timer;
-	    if (is_value(tref) && proc == c_p)
-		ref = tref;
-	    else {
-		write_ref_thing(hp,
-				trefn[0],
-				trefn[1],
-				trefn[2]);
-		ref = make_internal_ref(hp);
-		hp += REF_THING_SIZE;
-	    }
-	    msg = TUPLE3(hp, tag, ref, result);
+	msg = (async
+	       ? TUPLE3(hp, (cancel
+			     ? am_cancel_timer
+			     : am_read_timer), ref, result)
+	       : TUPLE2(hp, ref, result));
 
-	    ERTS_HLT_ASSERT(hp + 4 == hp_end);
+	ERTS_HLT_ASSERT(hp + (async ? 4 : 3) == hp_end);
 
-	}
-	erts_queue_message(proc, &proc_locks, bp, msg, NIL);
+	erts_queue_message(proc, &proc_locks, mp, msg, NIL);
 
 	if (c_p)
 	    proc_locks &= ~ERTS_PROC_LOCK_MAIN;
@@ -2093,16 +2077,19 @@ try_access_sched_remote_btm(ErtsSchedulerData *esdp,
 	}
     }
     else {
+	ErtsMessage *mp;
 	Eterm tag, res, msg;
 	Uint hsz;
 	Eterm *hp;
 	ErtsProcLocks proc_locks = ERTS_PROC_LOCK_MAIN;
+	ErlOffHeap *ohp;
 
 	hsz = 4;
 	if (time_left > (Sint64) MAX_SMALL)
 	    hsz += ERTS_SINT64_HEAP_SIZE(time_left);
 
-	hp = HAlloc(c_p, hsz);
+	mp = erts_alloc_message_heap(c_p, &proc_locks,
+				     hsz, &hp, &ohp);
 	if (cancel)
 	    tag = am_cancel_timer;
 	else
@@ -2117,7 +2104,7 @@ try_access_sched_remote_btm(ErtsSchedulerData *esdp,
 
 	msg = TUPLE3(hp, tag, tref, res);
 
-	erts_queue_message(c_p, &proc_locks, NULL, msg, NIL);
+	erts_queue_message(c_p, &proc_locks, mp, msg, NIL);
 
 	proc_locks &= ~ERTS_PROC_LOCK_MAIN;
 	if (proc_locks)
-- 
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