Merge branch 'rickard/ohmq/OTP-13047'

* rickard/ohmq/OTP-13047:
  Fragmented young heap generation and off_heap_message_queue option
  Refactor GC
  Introduce literal tag

Conflicts:
	erts/doc/src/erlang.xml
	erts/emulator/beam/erl_gc.c

1 files changed, 920 insertions, 589 deletions

diff --git a/erts/emulator/beam/erl_message.c b/erts/emulator/beam/erl_message.c
index ef52823287..79739501a8 100644
--- a/erts/emulator/beam/erl_message.c
+++ b/erts/emulator/beam/erl_message.c
@@ -33,8 +33,8 @@
 #include "erl_binary.h"
 #include "dtrace-wrapper.h"
 
-ERTS_SCHED_PREF_QUICK_ALLOC_IMPL(message,
-				 ErlMessage,
+ERTS_SCHED_PREF_QUICK_ALLOC_IMPL(message_ref,
+				 ErtsMessageRef,
 				 ERL_MESSAGE_BUF_SZ,
 				 ERTS_ALC_T_MSG_REF)
 
@@ -44,27 +44,20 @@ ERTS_SCHED_PREF_QUICK_ALLOC_IMPL(message,
 #undef HARD_DEBUG
 #endif
 
-
-
-
-#ifdef DEBUG
-static ERTS_INLINE int in_heapfrag(const Eterm* ptr, const ErlHeapFragment *bp)
+void
+init_message(void)
 {
-    return ((unsigned)(ptr - bp->mem) < bp->used_size);
+    init_message_ref_alloc();
 }
-#endif
 
-
-void
-init_message(void)
+void *erts_alloc_message_ref(void)
 {
-    init_message_alloc();
+    return (void *) message_ref_alloc();
 }
 
-void
-free_message(ErlMessage* mp)
+void erts_free_message_ref(void *mp)
 {
-    message_free(mp);
+    message_ref_free((ErtsMessageRef *) mp);
 }
 
 /* Allocate message buffer (size in words) */
@@ -74,7 +67,7 @@ new_message_buffer(Uint size)
     ErlHeapFragment* bp;
     bp = (ErlHeapFragment*) ERTS_HEAP_ALLOC(ERTS_ALC_T_HEAP_FRAG,
 					    ERTS_HEAP_FRAG_SIZE(size));
-    ERTS_INIT_HEAP_FRAG(bp, size);
+    ERTS_INIT_HEAP_FRAG(bp, size, size);
     return bp;
 }
 
@@ -203,83 +196,87 @@ free_message_buffer(ErlHeapFragment* bp)
     }while (bp != NULL);
 }
 
-static ERTS_INLINE void
-link_mbuf_to_proc(Process *proc, ErlHeapFragment *bp)
+void
+erts_cleanup_messages(ErtsMessage *msgp)
 {
-    if (bp) {
-	/* Link the message buffer */
-	bp->next = MBUF(proc);
-	MBUF(proc) = bp;
-	MBUF_SIZE(proc) += bp->used_size;
-	FLAGS(proc) |= F_FORCE_GC;
-
-	/* Move any off_heap's into the process */
-	if (bp->off_heap.first != NULL) {
-	    struct erl_off_heap_header** next_p = &bp->off_heap.first;
-	    while (*next_p != NULL) {
-		next_p = &((*next_p)->next);
+    ErtsMessage *mp = msgp;
+    while (mp) {
+	ErtsMessage *fmp;
+	ErlHeapFragment *bp;
+	if (is_non_value(ERL_MESSAGE_TERM(mp))) {
+	    if (is_not_immed(ERL_MESSAGE_TOKEN(mp))) {
+		bp = (ErlHeapFragment *) mp->data.dist_ext->ext_endp;
+		erts_cleanup_offheap(&bp->off_heap);
 	    }
-	    *next_p = MSO(proc).first;
-	    MSO(proc).first = bp->off_heap.first;
-	    bp->off_heap.first = NULL;
-	    OH_OVERHEAD(&(MSO(proc)), bp->off_heap.overhead);
+	    if (mp->data.dist_ext)
+		erts_free_dist_ext_copy(mp->data.dist_ext);
 	}
+	else {
+	    if (mp->data.attached != ERTS_MSG_COMBINED_HFRAG)
+		bp = mp->data.heap_frag;
+	    else {
+		bp = mp->hfrag.next;
+		erts_cleanup_offheap(&mp->hfrag.off_heap);
+	    }
+	    if (bp)
+		free_message_buffer(bp);
+	}
+	fmp = mp;
+	mp = mp->next;
+	erts_free_message(fmp);
     }
 }
 
-Eterm
-erts_msg_distext2heap(Process *pp,
-		      ErtsProcLocks *plcksp,
-		      ErlHeapFragment **bpp,
-		      Eterm *tokenp,
-		      ErtsDistExternal *dist_extp)
+ErtsMessage *
+erts_realloc_shrink_message(ErtsMessage *mp, Uint sz, Eterm *brefs, Uint brefs_size)
 {
-    Eterm msg;
-    Uint tok_sz = 0;
-    Eterm *hp = NULL;
-    ErtsHeapFactory factory;
-    Sint sz;
-
-    *bpp = NULL;
-    sz = erts_decode_dist_ext_size(dist_extp);
-    if (sz < 0)
-	goto decode_error;
-    if (is_not_nil(*tokenp)) {
-	ErlHeapFragment *heap_frag = erts_dist_ext_trailer(dist_extp);
-	tok_sz = heap_frag->used_size;
-	sz += tok_sz;
-    }
-    if (pp) {
-	ErlOffHeap *ohp;
-	hp = erts_alloc_message_heap(sz, bpp, &ohp, pp, plcksp);
-    }
-    else {
-	*bpp = new_message_buffer(sz);
-	hp = (*bpp)->mem;
-    }
-    erts_factory_message_init(&factory, pp, hp, *bpp);
-    msg = erts_decode_dist_ext(&factory, dist_extp);
-    if (is_non_value(msg))
-	goto decode_error;
-    if (is_not_nil(*tokenp)) {
-	ErlHeapFragment *heap_frag = erts_dist_ext_trailer(dist_extp);
-	hp = erts_produce_heap(&factory, tok_sz, 0);
-	*tokenp = copy_struct(*tokenp, tok_sz, &hp, factory.off_heap);
-	erts_cleanup_offheap(&heap_frag->off_heap);
+    ErtsMessage *nmp = erts_realloc(ERTS_ALC_T_MSG, mp,
+				    sizeof(ErtsMessage) + (sz - 1)*sizeof(Eterm));
+    if (nmp != mp) {
+	Eterm *sp = &mp->hfrag.mem[0];
+	Eterm *ep = sp + sz;
+	Sint offs = &nmp->hfrag.mem[0] - sp;
+	erts_offset_off_heap(&nmp->hfrag.off_heap, offs, sp, ep);
+	erts_offset_heap(&nmp->hfrag.mem[0], sz, offs, sp, ep);
+	if (brefs && brefs_size)
+	    erts_offset_heap_ptr(brefs, brefs_size, offs, sp, ep);
     }
-    erts_free_dist_ext_copy(dist_extp);
-    erts_factory_close(&factory);
-    return msg;
 
- decode_error:
-    if (is_not_nil(*tokenp)) {
-	ErlHeapFragment *heap_frag = erts_dist_ext_trailer(dist_extp);
-	erts_cleanup_offheap(&heap_frag->off_heap);
+    nmp->hfrag.used_size = sz;
+    nmp->hfrag.alloc_size = sz;
+
+    return nmp;
+}
+
+void
+erts_link_mbuf_to_proc(Process *proc, ErlHeapFragment *first_bp)
+{
+    if (first_bp) {
+	ErlHeapFragment *bp = first_bp;
+
+	while (1) {
+	    /* Move any off_heap's into the process */
+	    if (bp->off_heap.first != NULL) {
+		struct erl_off_heap_header** next_p = &bp->off_heap.first;
+		while (*next_p != NULL) {
+		    next_p = &((*next_p)->next);
+		}
+		*next_p = MSO(proc).first;
+		MSO(proc).first = bp->off_heap.first;
+		bp->off_heap.first = NULL;
+		OH_OVERHEAD(&(MSO(proc)), bp->off_heap.overhead);
+	    }
+	    MBUF_SIZE(proc) += bp->used_size;
+	    if (!bp->next)
+		break;
+	    bp = bp->next;
+	}
+
+	/* Link the message buffer */
+	bp->next = MBUF(proc);
+	MBUF(proc) = first_bp;
     }
-    erts_free_dist_ext_copy(dist_extp);
-    *bpp = NULL;
-    return THE_NON_VALUE;
- }
+}
 
 void
 erts_queue_dist_message(Process *rcvr,
@@ -287,7 +284,7 @@ erts_queue_dist_message(Process *rcvr,
 			ErtsDistExternal *dist_ext,
 			Eterm token)
 {
-    ErlMessage* mp;
+    ErtsMessage* mp;
 #ifdef USE_VM_PROBES
     Sint tok_label = 0;
     Sint tok_lastcnt = 0;
@@ -299,7 +296,17 @@ erts_queue_dist_message(Process *rcvr,
 
     ERTS_SMP_LC_ASSERT(*rcvr_locks == erts_proc_lc_my_proc_locks(rcvr));
 
-    mp = message_alloc();
+    mp = erts_alloc_message(0, NULL);
+    mp->data.dist_ext = dist_ext;
+
+    ERL_MESSAGE_TERM(mp) = THE_NON_VALUE;
+#ifdef USE_VM_PROBES
+    ERL_MESSAGE_DT_UTAG(mp) = NIL;
+    if (token == am_have_dt_utag)
+	ERL_MESSAGE_TOKEN(mp) = NIL;
+    else
+#endif
+	ERL_MESSAGE_TOKEN(mp) = token;
 
 #ifdef ERTS_SMP
     if (!(*rcvr_locks & ERTS_PROC_LOCK_MSGQ)) {
@@ -318,58 +325,40 @@ erts_queue_dist_message(Process *rcvr,
 	if (!(*rcvr_locks & ERTS_PROC_LOCK_MSGQ))
 	    erts_smp_proc_unlock(rcvr, ERTS_PROC_LOCK_MSGQ);
 	/* Drop message if receiver is exiting or has a pending exit ... */
-	if (is_not_nil(token)) {
-	    ErlHeapFragment *heap_frag;
-	    heap_frag = erts_dist_ext_trailer(mp->data.dist_ext);
-	    erts_cleanup_offheap(&heap_frag->off_heap);
-	}
-	erts_free_dist_ext_copy(dist_ext);
-	message_free(mp);
+	erts_cleanup_messages(mp);
     }
     else
 #endif
     if (IS_TRACED_FL(rcvr, F_TRACE_RECEIVE)) {
 	/* Ahh... need to decode it in order to trace it... */
-	ErlHeapFragment *mbuf;
-	Eterm msg;
 	if (!(*rcvr_locks & ERTS_PROC_LOCK_MSGQ))
 	    erts_smp_proc_unlock(rcvr, ERTS_PROC_LOCK_MSGQ);
-	message_free(mp);
-	msg = erts_msg_distext2heap(rcvr, rcvr_locks, &mbuf, &token, dist_ext);
-	if (is_value(msg))
+	if (!erts_decode_dist_message(rcvr, *rcvr_locks, mp, 0))
+	    erts_free_message(mp);
+	else {
+	    Eterm msg = ERL_MESSAGE_TERM(mp);
+	    token = ERL_MESSAGE_TOKEN(mp);
 #ifdef USE_VM_PROBES
-            if (DTRACE_ENABLED(message_queued)) {
-                DTRACE_CHARBUF(receiver_name, DTRACE_TERM_BUF_SIZE);
-
-                dtrace_proc_str(rcvr, receiver_name);
-                if (token != NIL && token != am_have_dt_utag) {
-                    tok_label = signed_val(SEQ_TRACE_T_LABEL(token));
-                    tok_lastcnt = signed_val(SEQ_TRACE_T_LASTCNT(token));
-                    tok_serial = signed_val(SEQ_TRACE_T_SERIAL(token));
-                }
-                DTRACE6(message_queued,
-                        receiver_name, size_object(msg), rcvr->msg.len,
-                        tok_label, tok_lastcnt, tok_serial);
-            }
+	    if (DTRACE_ENABLED(message_queued)) {
+		DTRACE_CHARBUF(receiver_name, DTRACE_TERM_BUF_SIZE);
+
+		dtrace_proc_str(rcvr, receiver_name);
+		if (token != NIL && token != am_have_dt_utag) {
+		    tok_label = signed_val(SEQ_TRACE_T_LABEL(token));
+		    tok_lastcnt = signed_val(SEQ_TRACE_T_LASTCNT(token));
+		    tok_serial = signed_val(SEQ_TRACE_T_SERIAL(token));
+		}
+		DTRACE6(message_queued,
+			receiver_name, size_object(msg), rcvr->msg.len,
+			tok_label, tok_lastcnt, tok_serial);
+	    }
 #endif
-	    erts_queue_message(rcvr, rcvr_locks, mbuf, msg, token);
+	    erts_queue_message(rcvr, rcvr_locks, mp, msg, token);
+	}
     }
     else {
 	/* Enqueue message on external format */
 
-	ERL_MESSAGE_TERM(mp) = THE_NON_VALUE;
-#ifdef USE_VM_PROBES
-	ERL_MESSAGE_DT_UTAG(mp) = NIL;
-	if (token == am_have_dt_utag) {
-	    ERL_MESSAGE_TOKEN(mp) = NIL;
-	} else {
-#endif
-	    ERL_MESSAGE_TOKEN(mp) = token;
-#ifdef USE_VM_PROBES
-	}
-#endif
-	mp->next = NULL;
-
 #ifdef USE_VM_PROBES
         if (DTRACE_ENABLED(message_queued)) {
             DTRACE_CHARBUF(receiver_name, DTRACE_TERM_BUF_SIZE);
@@ -388,7 +377,7 @@ erts_queue_dist_message(Process *rcvr,
                     tok_label, tok_lastcnt, tok_serial);
         }
 #endif
-	mp->data.dist_ext = dist_ext;
+
 	LINK_MESSAGE(rcvr, mp);
 
 	if (!(*rcvr_locks & ERTS_PROC_LOCK_MSGQ))
@@ -408,9 +397,9 @@ erts_queue_dist_message(Process *rcvr,
 static Sint
 queue_message(Process *c_p,
 	      Process* receiver,
-	      ErtsProcLocks *receiver_locks,
 	      erts_aint32_t *receiver_state,
-	      ErlHeapFragment* bp,
+	      ErtsProcLocks *receiver_locks,
+	      ErtsMessage* mp,
 	      Eterm message,
 	      Eterm seq_trace_token
 #ifdef USE_VM_PROBES
@@ -419,31 +408,24 @@ queue_message(Process *c_p,
     )
 {
     Sint res;
-    ErlMessage* mp;
     int locked_msgq = 0;
-    erts_aint_t state;
-
-#ifndef ERTS_SMP
-    ASSERT(bp != NULL || receiver->mbuf == NULL);
-#endif
+    erts_aint32_t state;
 
     ERTS_SMP_LC_ASSERT(*receiver_locks == erts_proc_lc_my_proc_locks(receiver));
 
-    mp = message_alloc();
-
-    if (receiver_state)
-	state = *receiver_state;
-    else
-	state = erts_smp_atomic32_read_acqb(&receiver->state);
-
 #ifdef ERTS_SMP
 
-    if (state & (ERTS_PSFLG_EXITING|ERTS_PSFLG_PENDING_EXIT))
-	goto exiting;
-
     if (!(*receiver_locks & ERTS_PROC_LOCK_MSGQ)) {
 	if (erts_smp_proc_trylock(receiver, ERTS_PROC_LOCK_MSGQ) == EBUSY) {
 	    ErtsProcLocks need_locks = ERTS_PROC_LOCK_MSGQ;
+
+	    if (receiver_state)
+		state = *receiver_state;
+	    else
+		state = erts_smp_atomic32_read_nob(&receiver->state);
+	    if (state & (ERTS_PSFLG_EXITING|ERTS_PSFLG_PENDING_EXIT))
+		goto exiting;
+
 	    if (*receiver_locks & ERTS_PROC_LOCK_STATUS) {
 		erts_smp_proc_unlock(receiver, ERTS_PROC_LOCK_STATUS);
 		need_locks |= ERTS_PROC_LOCK_STATUS;
@@ -451,13 +433,12 @@ queue_message(Process *c_p,
 	    erts_smp_proc_lock(receiver, need_locks);
 	}
 	locked_msgq = 1;
-	state = erts_smp_atomic32_read_nob(&receiver->state);
-	if (receiver_state)
-	    *receiver_state = state;
     }
 
 #endif
 
+    state = erts_smp_atomic32_read_nob(&receiver->state);
+
     if (state & (ERTS_PSFLG_PENDING_EXIT|ERTS_PSFLG_EXITING)) {
 #ifdef ERTS_SMP
     exiting:
@@ -465,9 +446,7 @@ queue_message(Process *c_p,
 	/* Drop message if receiver is exiting or has a pending exit... */
 	if (locked_msgq)
 	    erts_smp_proc_unlock(receiver, ERTS_PROC_LOCK_MSGQ);
-	if (bp)
-	    free_message_buffer(bp);
-	message_free(mp);
+	erts_cleanup_messages(mp);
 	return 0;
     }
 
@@ -476,13 +455,9 @@ queue_message(Process *c_p,
 #ifdef USE_VM_PROBES
     ERL_MESSAGE_DT_UTAG(mp) = dt_utag;
 #endif
-    mp->next = NULL;
-    mp->data.heap_frag = bp;
 
-#ifndef ERTS_SMP
     res = receiver->msg.len;
-#else
-    res = receiver->msg_inq.len;
+#ifdef ERTS_SMP
     if (*receiver_locks & ERTS_PROC_LOCK_MAIN) {
 	/*
 	 * We move 'in queue' to 'private queue' and place
@@ -492,7 +467,7 @@ queue_message(Process *c_p,
 	 * we don't need to include the 'in queue' in
 	 * the root set when garbage collecting.
 	 */
-	res += receiver->msg.len;
+	res += receiver->msg_inq.len;
 	ERTS_SMP_MSGQ_MV_INQ2PRIVQ(receiver);
 	LINK_MESSAGE_PRIVQ(receiver, mp);
     }
@@ -544,19 +519,19 @@ queue_message(Process *c_p,
 void
 #ifdef USE_VM_PROBES
 erts_queue_message_probe(Process* receiver, ErtsProcLocks *receiver_locks,
-                         ErlHeapFragment* bp,
+                         ErtsMessage* mp,
                          Eterm message, Eterm seq_trace_token, Eterm dt_utag)
 #else
 erts_queue_message(Process* receiver, ErtsProcLocks *receiver_locks,
-                   ErlHeapFragment* bp,
+                   ErtsMessage* mp,
                    Eterm message, Eterm seq_trace_token)
 #endif
 {
     queue_message(NULL,
 		  receiver,
-		  receiver_locks,
 		  NULL,
-		  bp,
+		  receiver_locks,
+		  mp,
 		  message,
 		  seq_trace_token
 #ifdef USE_VM_PROBES
@@ -565,246 +540,8 @@ erts_queue_message(Process* receiver, ErtsProcLocks *receiver_locks,
 	);
 }
 
-void
-erts_link_mbuf_to_proc(struct process *proc, ErlHeapFragment *bp)
-{
-    Eterm* htop = HEAP_TOP(proc);
-
-    link_mbuf_to_proc(proc, bp);
-    if (htop < HEAP_LIMIT(proc)) {
-	*htop = make_pos_bignum_header(HEAP_LIMIT(proc)-htop-1);
-	HEAP_TOP(proc) = HEAP_LIMIT(proc);
-    }
-}
-
-/*
- * Moves content of message buffer attached to a message into a heap.
- * The message buffer is deallocated.
- */
-void
-erts_move_msg_mbuf_to_heap(Eterm** hpp, ErlOffHeap* off_heap, ErlMessage *msg)
-{
-    struct erl_off_heap_header* oh;
-    Eterm term, token, *fhp, *hp;
-    Sint offs;
-    Uint sz;
-    ErlHeapFragment *bp;
-#ifdef USE_VM_PROBES
-    Eterm utag;
-#endif
-
-#ifdef HARD_DEBUG
-    struct erl_off_heap_header* dbg_oh_start = off_heap->first;
-    Eterm dbg_term, dbg_token;
-    ErlHeapFragment *dbg_bp;
-    Uint *dbg_hp, *dbg_thp_start;
-    Uint dbg_term_sz, dbg_token_sz;
-#ifdef USE_VM_PROBES
-    Eterm dbg_utag;
-    Uint dbg_utag_sz;
-#endif
-#endif
-
-    bp = msg->data.heap_frag;
-    term = ERL_MESSAGE_TERM(msg);
-    token = ERL_MESSAGE_TOKEN(msg);
-#ifdef USE_VM_PROBES
-    utag = ERL_MESSAGE_DT_UTAG(msg);
-#endif
-    if (!bp) {
-#ifdef USE_VM_PROBES
-	ASSERT(is_immed(term) && is_immed(token) && is_immed(utag));
-#else
-	ASSERT(is_immed(term) && is_immed(token));
-#endif
-	return;
-    }
-
-#ifdef HARD_DEBUG
-    dbg_term_sz = size_object(term);
-    dbg_token_sz = size_object(token);
-    dbg_bp = new_message_buffer(dbg_term_sz + dbg_token_sz);
-#ifdef USE_VM_PROBES
-    dbg_utag_sz = size_object(utag);
-    dbg_bp = new_message_buffer(dbg_term_sz + dbg_token_sz + dbg_utag_sz );
-#endif
-    /*ASSERT(dbg_term_sz + dbg_token_sz == erts_msg_used_frag_sz(msg));
-      Copied size may be smaller due to removed SubBins's or garbage.
-      Copied size may be larger due to duplicated shared terms.
-    */
-    dbg_hp = dbg_bp->mem;
-    dbg_term = copy_struct(term, dbg_term_sz, &dbg_hp, &dbg_bp->off_heap);
-    dbg_token = copy_struct(token, dbg_token_sz, &dbg_hp, &dbg_bp->off_heap);
-#ifdef USE_VM_PROBES
-    dbg_utag = copy_struct(utag, dbg_utag_sz, &dbg_hp, &dbg_bp->off_heap);
-#endif
-   dbg_thp_start = *hpp;
-#endif
-
-    if (bp->next != NULL) {
-	move_multi_frags(hpp, off_heap, bp, msg->m, 
-#ifdef USE_VM_PROBES
-			 3
-#else
-			 2
-#endif
-			 );
-	goto copy_done;
-    }
-
-    OH_OVERHEAD(off_heap, bp->off_heap.overhead);
-    sz = bp->used_size;
-
-    ASSERT(is_immed(term) || in_heapfrag(ptr_val(term),bp));
-    ASSERT(is_immed(token) || in_heapfrag(ptr_val(token),bp));
-
-    fhp = bp->mem;
-    hp = *hpp;
-    offs = hp - fhp;
-
-    oh = NULL;
-    while (sz--) {
-	Uint cpy_sz;
-	Eterm val = *fhp++;
-
-	switch (primary_tag(val)) {
-	case TAG_PRIMARY_IMMED1:
-	    *hp++ = val;
-	    break;
-	case TAG_PRIMARY_LIST:
-	case TAG_PRIMARY_BOXED:
-	    ASSERT(in_heapfrag(ptr_val(val), bp));
-	    *hp++ = offset_ptr(val, offs);
-	    break;
-	case TAG_PRIMARY_HEADER:
-	    *hp++ = val;
-	    switch (val & _HEADER_SUBTAG_MASK) {
-	    case ARITYVAL_SUBTAG:
-		break;
-	    case REFC_BINARY_SUBTAG:
-	    case FUN_SUBTAG:
-	    case EXTERNAL_PID_SUBTAG:
-	    case EXTERNAL_PORT_SUBTAG:
-	    case EXTERNAL_REF_SUBTAG:
-		oh = (struct erl_off_heap_header*) (hp-1);
-		cpy_sz = thing_arityval(val);
-		goto cpy_words;
-	    default:
-		cpy_sz = header_arity(val);
-
-	    cpy_words:
-		ASSERT(sz >= cpy_sz);
-		sz -= cpy_sz;
-		while (cpy_sz >= 8) {
-		    cpy_sz -= 8;
-		    *hp++ = *fhp++;
-		    *hp++ = *fhp++;
-		    *hp++ = *fhp++;
-		    *hp++ = *fhp++;
-		    *hp++ = *fhp++;
-		    *hp++ = *fhp++;
-		    *hp++ = *fhp++;
-		    *hp++ = *fhp++;
-		}
-		switch (cpy_sz) {
-		case 7: *hp++ = *fhp++;
-		case 6: *hp++ = *fhp++;
-		case 5: *hp++ = *fhp++;
-		case 4: *hp++ = *fhp++;
-		case 3: *hp++ = *fhp++;
-		case 2: *hp++ = *fhp++;
-		case 1: *hp++ = *fhp++;
-		default: break;
-		}
-		if (oh) {
-		    /* Add to offheap list */
-		    oh->next = off_heap->first;
-		    off_heap->first = oh;
-		    ASSERT(*hpp <= (Eterm*)oh);
-		    ASSERT(hp > (Eterm*)oh);
-		    oh = NULL;
-		}
-		break;
-	    }
-	    break;
-	}
-    }
-
-    ASSERT(bp->used_size == hp - *hpp);
-    *hpp = hp;
-
-    if (is_not_immed(token)) {
-	ASSERT(in_heapfrag(ptr_val(token), bp));
-	ERL_MESSAGE_TOKEN(msg) = offset_ptr(token, offs);
-#ifdef HARD_DEBUG
-	ASSERT(dbg_thp_start <= ptr_val(ERL_MESSAGE_TOKEN(msg)));
-	ASSERT(hp > ptr_val(ERL_MESSAGE_TOKEN(msg)));
-#endif
-    }
-
-    if (is_not_immed(term)) {
-	ASSERT(in_heapfrag(ptr_val(term),bp));
-	ERL_MESSAGE_TERM(msg) = offset_ptr(term, offs);
-#ifdef HARD_DEBUG
-	ASSERT(dbg_thp_start <= ptr_val(ERL_MESSAGE_TERM(msg)));
-	ASSERT(hp > ptr_val(ERL_MESSAGE_TERM(msg)));
-#endif
-    }
-#ifdef USE_VM_PROBES
-    if (is_not_immed(utag)) {
-	ASSERT(in_heapfrag(ptr_val(utag), bp));
-	ERL_MESSAGE_DT_UTAG(msg) = offset_ptr(utag, offs);
-#ifdef HARD_DEBUG
-	ASSERT(dbg_thp_start <= ptr_val(ERL_MESSAGE_DT_UTAG(msg)));
-	ASSERT(hp > ptr_val(ERL_MESSAGE_DT_UTAG(msg)));
-#endif
-    }
-#endif
-
-copy_done:
-
-#ifdef HARD_DEBUG
-    {
-	int i, j;
-	ErlHeapFragment* frag;
-	{
-	    struct erl_off_heap_header* dbg_oh = off_heap->first;
-	    i = j = 0;
-	    while (dbg_oh != dbg_oh_start) {
-		dbg_oh = dbg_oh->next;
-		i++;
-	    }
-	    for (frag=bp; frag; frag=frag->next) {
-		dbg_oh = frag->off_heap.first;
-		while (dbg_oh) {
-		    dbg_oh = dbg_oh->next;
-		    j++;
-		}
-	    }
-	    ASSERT(i == j);
-	}
-    }
-#endif
-	    
-
-    bp->off_heap.first = NULL;
-    free_message_buffer(bp);
-    msg->data.heap_frag = NULL;
-
-#ifdef HARD_DEBUG
-    ASSERT(eq(ERL_MESSAGE_TERM(msg), dbg_term));
-    ASSERT(eq(ERL_MESSAGE_TOKEN(msg), dbg_token));
-#ifdef USE_VM_PROBES
-    ASSERT(eq(ERL_MESSAGE_DT_UTAG(msg), dbg_utag));
-#endif
-    free_message_buffer(dbg_bp);
-#endif
-
-}
-
-
 Uint
-erts_msg_attached_data_size_aux(ErlMessage *msg)
+erts_msg_attached_data_size_aux(ErtsMessage *msg)
 {
     Sint sz;
     ASSERT(is_non_value(ERL_MESSAGE_TERM(msg)));
@@ -833,29 +570,72 @@ erts_msg_attached_data_size_aux(ErlMessage *msg)
     return sz;
 }
 
-void
-erts_move_msg_attached_data_to_heap(ErtsHeapFactory* factory,
-				    ErlMessage *msg)
+ErtsMessage *
+erts_try_alloc_message_on_heap(Process *pp,
+			       erts_aint32_t *psp,
+			       ErtsProcLocks *plp,
+			       Uint sz,
+			       Eterm **hpp,
+			       ErlOffHeap **ohpp,
+			       int *on_heap_p)
 {
-    if (is_value(ERL_MESSAGE_TERM(msg)))
-	erts_move_msg_mbuf_to_heap(&factory->hp, factory->off_heap, msg);
-    else if (msg->data.dist_ext) {
-	ASSERT(msg->data.dist_ext->heap_size >= 0);
-	if (is_not_nil(ERL_MESSAGE_TOKEN(msg))) {
-	    ErlHeapFragment *heap_frag;
-	    heap_frag = erts_dist_ext_trailer(msg->data.dist_ext);
-	    ERL_MESSAGE_TOKEN(msg) = copy_struct(ERL_MESSAGE_TOKEN(msg),
-						 heap_frag->used_size,
-						 &factory->hp,
-						 factory->off_heap);
-	    erts_cleanup_offheap(&heap_frag->off_heap);
+#ifdef ERTS_SMP
+    int locked_main = 0;
+#endif
+    ErtsMessage *mp;
+
+    ASSERT(!(*psp & ERTS_PSFLG_OFF_HEAP_MSGQ));
+
+    if (
+#if defined(ERTS_SMP)
+	*plp & ERTS_PROC_LOCK_MAIN
+#else
+	1
+#endif
+	) {
+#ifdef ERTS_SMP
+    try_on_heap:
+#endif
+	if ((*psp & (ERTS_PSFLG_EXITING|ERTS_PSFLG_PENDING_EXIT))
+	    || (pp->flags & F_DISABLE_GC)
+	    || HEAP_LIMIT(pp) - HEAP_TOP(pp) <= sz) {
+	    /*
+	     * The heap is either potentially in an inconsistent
+	     * state, or not large enough.
+	     */
+#ifdef ERTS_SMP
+	    if (locked_main) {
+		*plp &= ~ERTS_PROC_LOCK_MAIN;
+		erts_smp_proc_unlock(pp, ERTS_PROC_LOCK_MAIN);
+	    }
+#endif
+	    goto in_message_fragment;
 	}
-	ERL_MESSAGE_TERM(msg) = erts_decode_dist_ext(factory,
-						     msg->data.dist_ext);
-	erts_free_dist_ext_copy(msg->data.dist_ext);
-	msg->data.dist_ext = NULL;
+
+	*hpp = HEAP_TOP(pp);
+	HEAP_TOP(pp) = *hpp + sz;
+	*ohpp = &MSO(pp);
+	mp = erts_alloc_message(0, NULL);
+	mp->data.attached = NULL;
+	*on_heap_p = !0;
+    }
+#ifdef ERTS_SMP
+    else if (erts_smp_proc_trylock(pp, ERTS_PROC_LOCK_MAIN) == 0) {
+	locked_main = 1;
+	*psp = erts_smp_atomic32_read_nob(&pp->state);
+	*plp |= ERTS_PROC_LOCK_MAIN;
+	goto try_on_heap;
+    }
+#endif
+    else {
+    in_message_fragment:
+
+	mp = erts_alloc_message(sz, hpp);
+	*ohpp = sz == 0 ? NULL : &mp->hfrag.off_heap;
+	*on_heap_p = 0;
     }
-    /* else: bad external detected when calculating size */
+
+    return mp;
 }
 
 /*
@@ -870,7 +650,8 @@ erts_send_message(Process* sender,
 		  unsigned flags)
 {
     Uint msize;
-    ErlHeapFragment* bp = NULL;
+    ErtsMessage* mp;
+    ErlOffHeap *ohp;
     Eterm token = NIL;
     Sint res = 0;
 #ifdef USE_VM_PROBES
@@ -879,27 +660,31 @@ erts_send_message(Process* sender,
     Sint tok_label = 0;
     Sint tok_lastcnt = 0;
     Sint tok_serial = 0;
+    Eterm utag = NIL;
 #endif
+    erts_aint32_t receiver_state;
     BM_STOP_TIMER(system);
     BM_MESSAGE(message,sender,receiver);
     BM_START_TIMER(send);
 
  #ifdef USE_VM_PROBES
     *sender_name = *receiver_name = '\0';
-   if (DTRACE_ENABLED(message_send)) {
+    if (DTRACE_ENABLED(message_send)) {
         erts_snprintf(sender_name, sizeof(DTRACE_CHARBUF_NAME(sender_name)),
 		      "%T", sender->common.id);
         erts_snprintf(receiver_name, sizeof(DTRACE_CHARBUF_NAME(receiver_name)),
 		      "%T", receiver->common.id);
     }
 #endif
+
+    receiver_state = erts_smp_atomic32_read_nob(&receiver->state);
+
     if (SEQ_TRACE_TOKEN(sender) != NIL && !(flags & ERTS_SND_FLG_NO_SEQ_TRACE)) {
         Eterm* hp;
 	Eterm stoken = SEQ_TRACE_TOKEN(sender);
 	Uint seq_trace_size = 0;
 #ifdef USE_VM_PROBES
 	Uint dt_utag_size = 0;
-	Eterm utag = NIL;
 #endif
 
 	BM_SWAP_TIMER(send,size);
@@ -923,23 +708,32 @@ erts_send_message(Process* sender,
 	}
 #endif
 
-	bp = new_message_buffer(msize + seq_trace_size 
+	mp = erts_alloc_message_heap_state(receiver,
+					   &receiver_state,
+					   receiver_locks,
+					   (msize
 #ifdef USE_VM_PROBES
-				+ dt_utag_size
+					    + dt_utag_size
 #endif
-				);
-	hp = bp->mem;
+					    + seq_trace_size),
+					   &hp,
+					   &ohp);
 
         BM_SWAP_TIMER(send,copy);
-	token = copy_struct(stoken,
-			    seq_trace_size,
-			    &hp,
-			    &bp->off_heap);
+	if (is_immed(stoken))
+	    token = stoken;
+	else
+	    token = copy_struct(stoken, seq_trace_size, &hp, ohp);
+
+	if (is_not_immed(message))
+	    message = copy_struct(message, msize, &hp, ohp);
 
-	message = copy_struct(message, msize, &hp, &bp->off_heap);
 #ifdef USE_VM_PROBES
 	if (DT_UTAG_FLAGS(sender) & DT_UTAG_SPREADING) {
-	    utag = copy_struct(DT_UTAG(sender), dt_utag_size, &hp, &bp->off_heap);
+	    if (is_immed(DT_UTAG(sender)))
+		utag = DT_UTAG(sender);
+	    else
+		utag = copy_struct(DT_UTAG(sender), dt_utag_size, ohp);
 #ifdef DTRACE_TAG_HARDDEBUG
 	    erts_fprintf(stderr,
 			 "Dtrace -> (%T) Spreading tag (%T) with "
@@ -961,101 +755,49 @@ erts_send_message(Process* sender,
 		    msize, tok_label, tok_lastcnt, tok_serial);
         }
 #endif
-        res = queue_message(NULL,
-			    receiver,
-			    receiver_locks,
-			    NULL,
-			    bp,
-			    message,
-			    token
-#ifdef USE_VM_PROBES
-			    , utag
-#endif
-	    );
-        BM_SWAP_TIMER(send,system);
-    } else if (sender == receiver) {
-	/* Drop message if receiver has a pending exit ... */
-#ifdef ERTS_SMP
-	ErtsProcLocks need_locks = (~(*receiver_locks)
-				    & (ERTS_PROC_LOCK_MSGQ
-				       | ERTS_PROC_LOCK_STATUS));
-	if (need_locks) {
-	    *receiver_locks |= need_locks;
-	    if (erts_smp_proc_trylock(receiver, need_locks) == EBUSY) {
-		if (need_locks == ERTS_PROC_LOCK_MSGQ) {
-		    erts_smp_proc_unlock(receiver, ERTS_PROC_LOCK_STATUS);
-		    need_locks = ERTS_PROC_LOCK_MSGQ|ERTS_PROC_LOCK_STATUS;
-		}
-		erts_smp_proc_lock(receiver, need_locks);
-	    }
-	}
-	if (!ERTS_PROC_PENDING_EXIT(receiver))
-#endif
-	{
-	    ErlMessage* mp = message_alloc();
-
-            DTRACE6(message_send, sender_name, receiver_name,
-                    size_object(message), tok_label, tok_lastcnt, tok_serial);
-	    mp->data.attached = NULL;
-	    ERL_MESSAGE_TERM(mp) = message;
-	    ERL_MESSAGE_TOKEN(mp) = NIL;
-#ifdef USE_VM_PROBES
-	    ERL_MESSAGE_DT_UTAG(mp) = NIL;
-#endif
-	    mp->next = NULL;
-	    /*
-	     * We move 'in queue' to 'private queue' and place
-	     * message at the end of 'private queue' in order
-	     * to ensure that the 'in queue' doesn't contain
-	     * references into the heap. By ensuring this,
-	     * we don't need to include the 'in queue' in
-	     * the root set when garbage collecting.
-	     */
-	    
-	    ERTS_SMP_MSGQ_MV_INQ2PRIVQ(receiver);
-	    LINK_MESSAGE_PRIVQ(receiver, mp);
-
-	    res = receiver->msg.len;
-
-	    if (IS_TRACED_FL(receiver, F_TRACE_RECEIVE)) {
-		trace_receive(receiver, message);
-	    }
-	}
-        BM_SWAP_TIMER(send,system);
     } else {
-	ErlOffHeap *ohp;
         Eterm *hp;
-	erts_aint32_t state;
 
-	BM_SWAP_TIMER(send,size);
-	msize = size_object(message);
-	BM_SWAP_TIMER(size,send);
-	hp = erts_alloc_message_heap_state(msize,
-					   &bp,
-					   &ohp,
-					   receiver,
-					   receiver_locks,
-					   &state);
-	BM_SWAP_TIMER(send,copy);
-	message = copy_struct(message, msize, &hp, ohp);
-	BM_MESSAGE_COPIED(msz);
-	BM_SWAP_TIMER(copy,send);
+	if (receiver == sender && !(receiver_state & ERTS_PSFLG_OFF_HEAP_MSGQ)) {
+	    mp = erts_alloc_message(0, NULL);
+	    msize = 0;
+	}
+	else {
+	    BM_SWAP_TIMER(send,size);
+	    msize = size_object(message);
+	    BM_SWAP_TIMER(size,send);
+
+	    mp = erts_alloc_message_heap_state(receiver,
+					       &receiver_state,
+					       receiver_locks,
+					       msize,
+					       &hp,
+					       &ohp);
+	    BM_SWAP_TIMER(send,copy);
+	    if (is_not_immed(message))
+		message = copy_struct(message, msize, &hp, ohp);
+	    BM_MESSAGE_COPIED(msz);
+	    BM_SWAP_TIMER(copy,send);
+	}
         DTRACE6(message_send, sender_name, receiver_name,
                 msize, tok_label, tok_lastcnt, tok_serial);
-	res = queue_message(sender,
-			    receiver,
-			    receiver_locks,
-			    &state,
-			    bp,
-			    message,
-			    token
+    }
+
+    res = queue_message(sender,
+			receiver,
+			&receiver_state,
+			receiver_locks,
+			mp,
+			message,
+			token
 #ifdef USE_VM_PROBES
-			    , NIL
+			, utag
 #endif
-	    );
-        BM_SWAP_TIMER(send,system);
-    }
-   return res;
+	);
+
+    BM_SWAP_TIMER(send,system);
+    
+    return res;
 }
 
 /*
@@ -1075,7 +817,8 @@ erts_deliver_exit_message(Eterm from, Process *to, ErtsProcLocks *to_locksp,
     Uint sz_from;
     Eterm* hp;
     Eterm temptoken;
-    ErlHeapFragment* bp = NULL;
+    ErtsMessage* mp;
+    ErlOffHeap *ohp;
 
     if (token != NIL
 #ifdef USE_VM_PROBES
@@ -1087,36 +830,483 @@ erts_deliver_exit_message(Eterm from, Process *to, ErtsProcLocks *to_locksp,
 	sz_reason = size_object(reason);
 	sz_token = size_object(token);
 	sz_from = size_object(from);
-	bp = new_message_buffer(sz_reason + sz_from + sz_token + 4);
-	hp = bp->mem;
-	mess = copy_struct(reason, sz_reason, &hp, &bp->off_heap);
-	from_copy = copy_struct(from, sz_from, &hp, &bp->off_heap);
+	mp = erts_alloc_message_heap(to, to_locksp,
+				     sz_reason + sz_from + sz_token + 4,
+				     &hp, &ohp);
+	mess = copy_struct(reason, sz_reason, &hp, ohp);
+	from_copy = copy_struct(from, sz_from, &hp, ohp);
 	save = TUPLE3(hp, am_EXIT, from_copy, mess);
 	hp += 4;
 	/* the trace token must in this case be updated by the caller */
 	seq_trace_output(token, save, SEQ_TRACE_SEND, to->common.id, NULL);
-	temptoken = copy_struct(token, sz_token, &hp, &bp->off_heap);
-	erts_queue_message(to, to_locksp, bp, save, temptoken);
+	temptoken = copy_struct(token, sz_token, &hp, ohp);
+	erts_queue_message(to, to_locksp, mp, save, temptoken);
     } else {
-	ErlOffHeap *ohp;
 	sz_reason = size_object(reason);
 	sz_from = IS_CONST(from) ? 0 : size_object(from);
 
-	hp = erts_alloc_message_heap(sz_reason+sz_from+4,
-				     &bp,
-				     &ohp,
-				     to,
-				     to_locksp);
+	mp = erts_alloc_message_heap(to, to_locksp,
+				     sz_reason+sz_from+4, &hp, &ohp);
 
 	mess = copy_struct(reason, sz_reason, &hp, ohp);
 	from_copy = (IS_CONST(from)
 		     ? from
 		     : copy_struct(from, sz_from, &hp, ohp));
 	save = TUPLE3(hp, am_EXIT, from_copy, mess);
-	erts_queue_message(to, to_locksp, bp, save, NIL);
+	erts_queue_message(to, to_locksp, mp, save, NIL);
     }
 }
 
+void erts_save_message_in_proc(Process *p, ErtsMessage *msgp)
+{
+    ErlHeapFragment *hfp;
+
+    if (msgp->data.attached == ERTS_MSG_COMBINED_HFRAG)
+	hfp = &msgp->hfrag;
+    else if (msgp->data.attached) {
+	hfp = msgp->data.heap_frag;
+    }
+    else {
+	erts_free_message(msgp);
+	return; /* Nothing to save */
+    }
+
+    while (1) {
+	struct erl_off_heap_header *ohhp = hfp->off_heap.first;
+	if (ohhp) {
+	    for ( ; ohhp->next; ohhp = ohhp->next)
+		;
+	    ohhp->next = p->off_heap.first;
+	    p->off_heap.first = hfp->off_heap.first;
+	    hfp->off_heap.first = NULL;
+	}
+	p->off_heap.overhead += hfp->off_heap.overhead;
+	hfp->off_heap.overhead = 0;
+	p->mbuf_sz += hfp->used_size;
+
+	if (!hfp->next)
+	    break;
+	hfp = hfp->next;
+    }
+
+    msgp->next = p->msg_frag;
+    p->msg_frag = msgp;
+}
+
+Sint
+erts_move_messages_off_heap(Process *c_p)
+{
+    int reds = 1;
+    /*
+     * Move all messages off heap. This *only* occurs when the
+     * process had off heap message disabled and just enabled
+     * it...
+     */
+    ErtsMessage *mp;
+
+    reds += c_p->msg.len / 10;
+
+    ASSERT(erts_smp_atomic32_read_nob(&c_p->state)
+	   & ERTS_PSFLG_OFF_HEAP_MSGQ);
+    ASSERT(c_p->flags & F_OFF_HEAP_MSGQ_CHNG);
+
+    for (mp = c_p->msg.first; mp; mp = mp->next) {
+	Uint msg_sz, token_sz;
+#ifdef USE_VM_PROBES
+	Uint utag_sz;
+#endif
+	Eterm *hp;
+	ErlHeapFragment *hfrag;
+
+	if (mp->data.attached)
+	    continue;
+
+	if (is_immed(ERL_MESSAGE_TERM(mp))
+#ifdef USE_VM_PROBES
+	    && is_immed(ERL_MESSAGE_DT_UTAG(mp))
+#endif
+	    && is_not_immed(ERL_MESSAGE_TOKEN(mp)))
+	    continue;
+
+	/*
+	 * The message refers into the heap. Copy the message
+	 * from the heap into a heap fragment and attach
+	 * it to the message...
+	 */
+	msg_sz = size_object(ERL_MESSAGE_TERM(mp));
+#ifdef USE_VM_PROBES
+	utag_sz = size_object(ERL_MESSAGE_DT_UTAG(mp));
+#endif
+	token_sz = size_object(ERL_MESSAGE_TOKEN(mp));
+
+	hfrag = new_message_buffer(msg_sz
+#ifdef USE_VM_PROBES
+				   + utag_sz
+#endif
+				   + token_sz);
+	hp = hfrag->mem;
+	if (is_not_immed(ERL_MESSAGE_TERM(mp)))
+	    ERL_MESSAGE_TERM(mp) = copy_struct(ERL_MESSAGE_TERM(mp),
+					       msg_sz, &hp,
+					       &hfrag->off_heap);
+	if (is_not_immed(ERL_MESSAGE_TOKEN(mp)))
+	    ERL_MESSAGE_TOKEN(mp) = copy_struct(ERL_MESSAGE_TOKEN(mp),
+						token_sz, &hp,
+						&hfrag->off_heap);
+#ifdef USE_VM_PROBES
+	if (is_not_immed(ERL_MESSAGE_DT_UTAG(mp)))
+	    ERL_MESSAGE_DT_UTAG(mp) = copy_struct(ERL_MESSAGE_DT_UTAG(mp),
+						  utag_sz, &hp,
+						  &hfrag->off_heap);
+#endif
+	mp->data.heap_frag = hfrag;
+	reds += 1;
+    }
+
+    return reds;
+}
+
+Sint
+erts_complete_off_heap_message_queue_change(Process *c_p)
+{
+    int reds = 1;
+
+    ERTS_SMP_LC_ASSERT(ERTS_PROC_LOCK_MAIN == erts_proc_lc_my_proc_locks(c_p));
+    ASSERT(c_p->flags & F_OFF_HEAP_MSGQ_CHNG);
+    ASSERT(erts_smp_atomic32_read_nob(&c_p->state) & ERTS_PSFLG_OFF_HEAP_MSGQ);
+
+    /*
+     * This job was first initiated when the process changed
+     * "off heap message queue" state from false to true. Since
+     * then ERTS_PSFLG_OFF_HEAP_MSGQ has been set. However, the
+     * state change might have been changed again (multiple times)
+     * since then. Check users last requested state (the flag
+     * F_OFF_HEAP_MSGQ), and make the state consistent with that.
+     */
+
+    if (!(c_p->flags & F_OFF_HEAP_MSGQ))
+	erts_smp_atomic32_read_band_nob(&c_p->state,
+					~ERTS_PSFLG_OFF_HEAP_MSGQ);
+    else {
+	reds += 2;
+	erts_smp_proc_lock(c_p, ERTS_PROC_LOCK_MSGQ);
+	ERTS_SMP_MSGQ_MV_INQ2PRIVQ(c_p);
+	erts_smp_proc_unlock(c_p, ERTS_PROC_LOCK_MSGQ);
+	reds += erts_move_messages_off_heap(c_p);
+    }
+    c_p->flags &= ~F_OFF_HEAP_MSGQ_CHNG;
+    return reds;
+}
+
+typedef struct {
+    Eterm pid;
+    ErtsThrPrgrLaterOp lop;
+} ErtsChangeOffHeapMessageQueue;
+
+static void
+change_off_heap_msgq(void *vcohmq)
+{
+    ErtsChangeOffHeapMessageQueue *cohmq;
+    /*
+     * Now we've waited thread progress which ensures that all
+     * messages to the process are enqueued off heap. Schedule
+     * completion of this change as a system task on the process
+     * itself. This in order to avoid lock contention on its
+     * main lock. We will be called in
+     * erts_complete_off_heap_message_queue_change() (above) when
+     * the system task has been selected for execution.
+     */
+    cohmq = (ErtsChangeOffHeapMessageQueue *) vcohmq;
+    erts_schedule_complete_off_heap_message_queue_change(cohmq->pid);
+    erts_free(ERTS_ALC_T_MSGQ_CHNG, vcohmq);
+}
+
+Eterm
+erts_change_off_heap_message_queue_state(Process *c_p, int enable)
+{
+
+#ifdef DEBUG
+    if (c_p->flags & F_OFF_HEAP_MSGQ) {
+	ASSERT(erts_smp_atomic32_read_nob(&c_p->state)
+	       & ERTS_PSFLG_OFF_HEAP_MSGQ);
+    }
+    else {
+	if (c_p->flags & F_OFF_HEAP_MSGQ_CHNG) {
+	    ASSERT(erts_smp_atomic32_read_nob(&c_p->state)
+		   & ERTS_PSFLG_OFF_HEAP_MSGQ);
+	}
+	else {
+	    ASSERT(!(erts_smp_atomic32_read_nob(&c_p->state)
+		     & ERTS_PSFLG_OFF_HEAP_MSGQ));
+	}
+    }
+#endif
+
+    if (c_p->flags & F_OFF_HEAP_MSGQ) {
+	/* Off heap message queue is enabled */
+
+	if (!enable) {
+	    c_p->flags &= ~F_OFF_HEAP_MSGQ;
+	    /*
+	     * We are not allowed to clear ERTS_PSFLG_OFF_HEAP_MSGQ
+	     * if a change is ongoing. It will be adjusted when the
+	     * change completes...
+	     */
+	    if (!(c_p->flags & F_OFF_HEAP_MSGQ_CHNG)) {
+		/* Safe to clear ERTS_PSFLG_OFF_HEAP_MSGQ... */
+		erts_smp_atomic32_read_band_nob(&c_p->state,
+						~ERTS_PSFLG_OFF_HEAP_MSGQ);
+	    }
+	}
+
+	return am_true; /* Old state */
+    }
+
+    /* Off heap message queue is disabled */
+
+    if (enable) {
+	c_p->flags |= F_OFF_HEAP_MSGQ;
+	/*
+	 * We do not have to schedule a change if
+	 * we have an ongoing change...
+	 */
+	if (!(c_p->flags & F_OFF_HEAP_MSGQ_CHNG)) {
+	    ErtsChangeOffHeapMessageQueue *cohmq;
+	    /*
+	     * Need to set ERTS_PSFLG_OFF_HEAP_MSGQ and wait
+	     * thread progress before completing the change in
+	     * order to ensure that all senders observe that
+	     * messages should be passed off heap. When the
+	     * change has completed, GC does not need to inspect
+	     * the message queue at all.
+	     */
+	    erts_smp_atomic32_read_bor_nob(&c_p->state,
+					   ERTS_PSFLG_OFF_HEAP_MSGQ);
+	    c_p->flags |= F_OFF_HEAP_MSGQ_CHNG;
+	    cohmq = erts_alloc(ERTS_ALC_T_MSGQ_CHNG,
+			       sizeof(ErtsChangeOffHeapMessageQueue));
+	    cohmq->pid = c_p->common.id;
+	    erts_schedule_thr_prgr_later_op(change_off_heap_msgq,
+					    (void *) cohmq,
+					    &cohmq->lop);
+	}
+    }
+
+    return am_false; /* Old state */
+}
+
+int
+erts_decode_dist_message(Process *proc, ErtsProcLocks proc_locks,
+			 ErtsMessage *msgp, int force_off_heap)
+{
+    ErtsHeapFactory factory;
+    Eterm msg;
+    ErlHeapFragment *bp;
+    Sint need;
+    int decode_in_heap_frag;
+
+    decode_in_heap_frag = (force_off_heap
+			   || !(proc_locks & ERTS_PROC_LOCK_MAIN)
+			   || (proc->flags & F_OFF_HEAP_MSGQ));
+
+    if (msgp->data.dist_ext->heap_size >= 0)
+	need = msgp->data.dist_ext->heap_size;
+    else {
+	need = erts_decode_dist_ext_size(msgp->data.dist_ext);
+	if (need < 0) {
+	    /* bad msg; remove it... */
+	    if (is_not_immed(ERL_MESSAGE_TOKEN(msgp))) {
+		bp = erts_dist_ext_trailer(msgp->data.dist_ext);
+		erts_cleanup_offheap(&bp->off_heap);
+	    }
+	    erts_free_dist_ext_copy(msgp->data.dist_ext);
+	    msgp->data.dist_ext = NULL;
+	    return 0;
+	}
+
+	msgp->data.dist_ext->heap_size = need;
+    }
+
+    if (is_not_immed(ERL_MESSAGE_TOKEN(msgp))) {
+	bp = erts_dist_ext_trailer(msgp->data.dist_ext);
+	need += bp->used_size;
+    }
+
+    if (decode_in_heap_frag)
+	erts_factory_heap_frag_init(&factory, new_message_buffer(need));
+    else
+	erts_factory_proc_prealloc_init(&factory, proc, need);
+
+    ASSERT(msgp->data.dist_ext->heap_size >= 0);
+    if (is_not_immed(ERL_MESSAGE_TOKEN(msgp))) {
+	ErlHeapFragment *heap_frag;
+	heap_frag = erts_dist_ext_trailer(msgp->data.dist_ext);
+	ERL_MESSAGE_TOKEN(msgp) = copy_struct(ERL_MESSAGE_TOKEN(msgp),
+					      heap_frag->used_size,
+					      &factory.hp,
+					      factory.off_heap);
+	erts_cleanup_offheap(&heap_frag->off_heap);
+    }
+
+    msg = erts_decode_dist_ext(&factory, msgp->data.dist_ext);
+    ERL_MESSAGE_TERM(msgp) = msg;
+    erts_free_dist_ext_copy(msgp->data.dist_ext);
+    msgp->data.attached = NULL;
+
+    if (is_non_value(msg)) {
+	erts_factory_undo(&factory);
+	return 0;
+    }
+
+    erts_factory_trim_and_close(&factory, msgp->m,
+				ERL_MESSAGE_REF_ARRAY_SZ);
+
+    ASSERT(!msgp->data.heap_frag);
+
+    if (decode_in_heap_frag)
+	msgp->data.heap_frag = factory.heap_frags;
+
+    return 1;
+}
+
+/*
+ * ERTS_INSPECT_MSGQ_KEEP_OH_MSGS == 0 will move off heap messages
+ * into the heap of the inspected process if off_heap_message_queue
+ * is false when process_info(_, messages) is called. That is, the
+ * following GC will have more data in the rootset compared to the
+ * scenario when process_info(_, messages) had not been called.
+ *
+ * ERTS_INSPECT_MSGQ_KEEP_OH_MSGS != 0 will keep off heap messages
+ * off heap when process_info(_, messages) is called regardless of
+ * the off_heap_message_queue setting of the process. That is, it
+ * will change the following execution of the process as little as
+ * possible.
+ */
+#define ERTS_INSPECT_MSGQ_KEEP_OH_MSGS 1
+
+Uint
+erts_prep_msgq_for_inspection(Process *c_p, Process *rp,
+			      ErtsProcLocks rp_locks, ErtsMessageInfo *mip)
+{
+    Uint tot_heap_size;
+    ErtsMessage* mp;
+    Sint i;
+    int self_on_heap;
+    
+    /*
+     * Prepare the message queue for inspection
+     * by process_info().
+     *
+     *
+     * - Decode all messages on external format
+     * - Remove all corrupt dist messages from queue
+     * - Save pointer to, and heap size need of each
+     *   message in the mip array.
+     * - Return total heap size need for all messages
+     *   that needs to be copied.
+     *
+     * If ERTS_INSPECT_MSGQ_KEEP_OH_MSGS == 0:
+     * - In case off heap messages is disabled and
+     *   we are inspecting our own queue, move all
+     *   off heap data into the heap.
+     */
+
+    self_on_heap = c_p == rp && !(c_p->flags & F_OFF_HEAP_MSGQ);
+
+    tot_heap_size = 0;
+    i = 0;
+    mp = rp->msg.first;
+    while (mp) {
+	Eterm msg = ERL_MESSAGE_TERM(mp);
+
+	mip[i].size = 0;
+
+	if (is_non_value(msg)) {
+	    /* Dist message on external format; decode it... */
+	    if (mp->data.attached)
+		erts_decode_dist_message(rp, rp_locks, mp,
+					 ERTS_INSPECT_MSGQ_KEEP_OH_MSGS);
+
+	    msg = ERL_MESSAGE_TERM(mp);
+
+	    if (is_non_value(msg)) {
+		ErtsMessage **mpp;
+		ErtsMessage *bad_mp = mp;
+		/*
+		 * Bad distribution message; remove
+		 * it from the queue...
+		 */
+		ASSERT(!mp->data.attached);
+
+		mpp = i == 0 ? &rp->msg.first : &mip[i-1].msgp->next;
+
+		if (rp->msg.save == &bad_mp->next)
+		    rp->msg.save = mpp;
+		if (rp->msg.last == &bad_mp->next)
+		    rp->msg.last = mpp;
+		mp = mp->next;
+		*mpp = mp;
+		rp->msg.len--;
+		bad_mp->next = NULL;
+		erts_cleanup_messages(bad_mp);
+		continue;
+	    }
+	}
+
+	ASSERT(is_value(msg));
+
+#if ERTS_INSPECT_MSGQ_KEEP_OH_MSGS
+	if (is_not_immed(msg) && (!self_on_heap || mp->data.attached)) {
+	    Uint sz = size_object(msg);
+	    mip[i].size = sz;
+	    tot_heap_size += sz;
+	}
+#else
+	if (self_on_heap) {
+	    if (mp->data.attached) {
+		ErtsMessage *tmp = NULL;
+		if (mp->data.attached != ERTS_MSG_COMBINED_HFRAG) {
+		    erts_link_mbuf_to_proc(rp, mp->data.heap_frag);
+		    mp->data.attached = NULL;
+		}
+		else {
+		    /*
+		     * Need to replace the message reference since
+		     * we will get references to the message data
+		     * from the heap...
+		     */
+		    ErtsMessage **mpp;
+		    tmp = erts_alloc_message(0, NULL);
+		    sys_memcpy((void *) tmp->m, (void *) mp->m,
+			       sizeof(Eterm)*ERL_MESSAGE_REF_ARRAY_SZ); 
+		    mpp = i == 0 ? &rp->msg.first : &mip[i-1].msgp->next;
+		    tmp->next = mp->next;
+		    if (rp->msg.save == &mp->next)
+			rp->msg.save = &tmp->next;
+		    if (rp->msg.last == &mp->next)
+			rp->msg.last = &tmp->next;
+		    *mpp = tmp;
+		    erts_save_message_in_proc(rp, mp);
+		    mp = tmp;
+		}
+	    }
+	}
+	else if (is_not_immed(msg)) {
+	    Uint sz = size_object(msg);
+	    mip[i].size = sz;
+	    tot_heap_size += sz;
+	}
+
+#endif
+
+	mip[i].msgp = mp;
+	i++;
+	mp = mp->next;
+    }
+
+    return tot_heap_size;
+}
+
 void erts_factory_proc_init(ErtsHeapFactory* factory,
 			    Process* p)
 {
@@ -1127,47 +1317,138 @@ void erts_factory_proc_prealloc_init(ErtsHeapFactory* factory,
 				     Process* p,
 				     Sint size)
 {
+    ErlHeapFragment *bp = p->mbuf;
     factory->mode     = FACTORY_HALLOC;
     factory->p        = p;
     factory->hp_start = HAlloc(p, size);
     factory->hp       = factory->hp_start;
     factory->hp_end   = factory->hp_start + size;
     factory->off_heap = &p->off_heap;
+    factory->message  = NULL;
     factory->off_heap_saved.first    = p->off_heap.first;
     factory->off_heap_saved.overhead = p->off_heap.overhead;
-    factory->heap_frags_saved = p->mbuf;
+    factory->heap_frags_saved = bp;
+    factory->heap_frags_saved_used = bp ? bp->used_size : 0;
     factory->heap_frags = NULL; /* not used */
     factory->alloc_type = 0; /* not used */
 }
 
-void erts_factory_message_init(ErtsHeapFactory* factory,
-			       Process* rp,
-			       Eterm* hp,
-			       ErlHeapFragment* bp)
+void erts_factory_heap_frag_init(ErtsHeapFactory* factory,
+				 ErlHeapFragment* bp)
+{
+    factory->mode     = FACTORY_HEAP_FRAGS;
+    factory->p        = NULL;
+    factory->hp_start = bp->mem;
+    factory->hp       = bp->mem;
+    factory->hp_end   = bp->mem + bp->alloc_size;
+    factory->off_heap = &bp->off_heap;
+    factory->message  = NULL;
+    factory->heap_frags = bp;
+    factory->heap_frags_saved = NULL;
+    factory->heap_frags_saved_used = 0;
+    factory->alloc_type = ERTS_ALC_T_HEAP_FRAG;
+    ASSERT(!bp->next);
+    factory->off_heap_saved.first    = factory->off_heap->first;
+    factory->off_heap_saved.overhead = factory->off_heap->overhead;
+
+    ASSERT(factory->hp >= factory->hp_start && factory->hp <= factory->hp_end);
+}
+
+
+ErtsMessage *
+erts_factory_message_create(ErtsHeapFactory* factory,
+			    Process *proc,
+			    ErtsProcLocks *proc_locksp,
+			    Uint sz)
+{
+    Eterm *hp;
+    ErlOffHeap *ohp;
+    ErtsMessage *msgp;
+    int on_heap;
+    erts_aint32_t state;
+
+    state = erts_smp_atomic32_read_nob(&proc->state);
+
+    if (state & ERTS_PSFLG_OFF_HEAP_MSGQ) {
+	msgp = erts_alloc_message(sz, &hp);
+	ohp = sz == 0 ? NULL : &msgp->hfrag.off_heap;
+	on_heap = 0;
+    }
+    else {
+	msgp = erts_try_alloc_message_on_heap(proc, &state,
+					      proc_locksp,
+					      sz, &hp, &ohp,
+					      &on_heap);
+    }
+
+    if (on_heap) {
+	ASSERT(*proc_locksp & ERTS_PROC_LOCK_MAIN);
+	ASSERT(ohp == &proc->off_heap);
+	factory->mode = FACTORY_HALLOC;
+	factory->p = proc;
+	factory->heap_frags_saved = proc->mbuf;
+	factory->heap_frags_saved_used = proc->mbuf ? proc->mbuf->used_size : 0;
+    }
+    else {
+	factory->mode = FACTORY_MESSAGE;
+	factory->p = NULL;
+	factory->heap_frags_saved = NULL;
+	factory->heap_frags_saved_used = 0;
+
+	if (msgp->data.attached == ERTS_MSG_COMBINED_HFRAG) {
+	    ASSERT(!msgp->hfrag.next);
+	    factory->heap_frags = NULL;
+	}
+	else {
+	    ASSERT(!msgp->data.heap_frag
+		   || !msgp->data.heap_frag->next);
+	    factory->heap_frags = msgp->data.heap_frag;
+	}
+    }
+    factory->hp_start = hp;
+    factory->hp       = hp;
+    factory->hp_end   = hp + sz;
+    factory->message  = msgp;
+    factory->off_heap = ohp;
+    factory->alloc_type = ERTS_ALC_T_HEAP_FRAG;
+    if (ohp) {
+	factory->off_heap_saved.first    = ohp->first;
+	factory->off_heap_saved.overhead = ohp->overhead;
+    }
+    else {
+	factory->off_heap_saved.first    = NULL;
+	factory->off_heap_saved.overhead = 0;
+    }
+
+    ASSERT(factory->hp >= factory->hp_start && factory->hp <= factory->hp_end);
+
+    return msgp;
+}
+
+void erts_factory_selfcontained_message_init(ErtsHeapFactory* factory,
+					     ErtsMessage *msgp,
+					     Eterm *hp)
 {
-    if (bp) {
-	factory->mode     = FACTORY_HEAP_FRAGS;
-	factory->p        = NULL;
-	factory->hp_start = bp->mem;
-	factory->hp       = hp ? hp : bp->mem;
-	factory->hp_end   = bp->mem + bp->alloc_size;
-	factory->off_heap = &bp->off_heap;
-        factory->heap_frags = bp;
-        factory->heap_frags_saved = bp;
-        factory->alloc_type = ERTS_ALC_T_HEAP_FRAG;
-        ASSERT(!bp->next);
+    ErlHeapFragment* bp;
+    if (msgp->data.attached == ERTS_MSG_COMBINED_HFRAG) {
+	bp = &msgp->hfrag;
+	factory->heap_frags = NULL;
     }
     else {
-	factory->mode     = FACTORY_HALLOC;
-	factory->p        = rp;
-	factory->hp_start = hp;
-	factory->hp       = hp;
-	factory->hp_end   = HEAP_TOP(rp);
-	factory->off_heap = &rp->off_heap;
-        factory->heap_frags_saved = rp->mbuf;
-        factory->heap_frags = NULL; /* not used */
-        factory->alloc_type = 0; /* not used */
+	bp = msgp->data.heap_frag;
+	factory->heap_frags = bp;
     }
+    factory->mode     = FACTORY_MESSAGE;
+    factory->p        = NULL;
+    factory->hp_start = bp->mem;
+    factory->hp       = hp;
+    factory->hp_end   = bp->mem + bp->alloc_size;
+    factory->message  = msgp;
+    factory->off_heap = &bp->off_heap;
+    factory->heap_frags_saved = NULL;
+    factory->heap_frags_saved_used = 0;
+    factory->alloc_type = ERTS_ALC_T_HEAP_FRAG;
+    ASSERT(!bp->next);
     factory->off_heap_saved.first    = factory->off_heap->first;
     factory->off_heap_saved.overhead = factory->off_heap->overhead;
 
@@ -1230,8 +1511,16 @@ static void reserve_heap(ErtsHeapFactory* factory, Uint need, Uint xtra)
 	factory->hp_end = factory->hp + need;
 	return;
 
-    case FACTORY_HEAP_FRAGS:
-	bp = factory->heap_frags;
+    case FACTORY_MESSAGE:
+	if (!factory->heap_frags) {
+	    ASSERT(factory->message->data.attached == ERTS_MSG_COMBINED_HFRAG);
+	    bp = &factory->message->hfrag;
+	}
+	else {
+	    /* Fall through */
+	case FACTORY_HEAP_FRAGS:
+	    bp = factory->heap_frags;
+	}
 
         if (bp) {
 	    ASSERT(factory->hp > bp->mem);
@@ -1269,8 +1558,23 @@ void erts_factory_close(ErtsHeapFactory* factory)
 	HRelease(factory->p, factory->hp_end, factory->hp);
 	break;
 
-    case FACTORY_HEAP_FRAGS:
-	bp = factory->heap_frags;
+    case FACTORY_MESSAGE:
+	if (!factory->heap_frags) {
+	    if (factory->message->data.attached == ERTS_MSG_COMBINED_HFRAG)
+		bp = &factory->message->hfrag;
+	    else
+		bp = NULL;
+	}
+	else {
+	    if (factory->message->data.attached	== ERTS_MSG_COMBINED_HFRAG)
+		factory->message->hfrag.next = factory->heap_frags;
+	    else
+		factory->message->data.heap_frag = factory->heap_frags;
+
+	    /* Fall through */
+	case FACTORY_HEAP_FRAGS:
+	    bp = factory->heap_frags;
+	}
 
 	if (bp) {
 	    ASSERT(factory->hp >= bp->mem);
@@ -1291,17 +1595,47 @@ void erts_factory_close(ErtsHeapFactory* factory)
 void erts_factory_trim_and_close(ErtsHeapFactory* factory,
 				 Eterm *brefs, Uint brefs_size)
 {
-    if (factory->mode == FACTORY_HEAP_FRAGS) {
-        ErlHeapFragment* bp = factory->heap_frags;
+    ErlHeapFragment *bp;
+
+    switch (factory->mode) {
+    case FACTORY_MESSAGE: {
+	ErtsMessage *mp = factory->message;
+	if (mp->data.attached == ERTS_MSG_COMBINED_HFRAG) {
+	    if (!mp->hfrag.next) {
+		Uint sz = factory->hp - factory->hp_start;
+		mp = erts_shrink_message(mp, sz, brefs, brefs_size);
+		factory->message = mp;
+		factory->mode = FACTORY_CLOSED;
+		return;
+	    }
+	    /*else we don't trim multi fragmented messages for now (off_heap...) */
+	    break;
+	}
+	/* Fall through... */
+    }
+    case FACTORY_HEAP_FRAGS:
+	bp = factory->heap_frags;
+	if (!bp)
+	    break;
         if (bp->next == NULL) {
             Uint used_sz = factory->hp - bp->mem;
             ASSERT(used_sz <= bp->alloc_size);
-            factory->heap_frags = erts_resize_message_buffer(bp, used_sz,
-                                                             brefs, brefs_size);
+	    if (used_sz > 0)
+		bp = erts_resize_message_buffer(bp, used_sz,
+						brefs, brefs_size);
+	    else {
+		free_message_buffer(bp);
+		bp = NULL;
+	    }
+	    factory->heap_frags = bp;
+	    if (factory->mode == FACTORY_MESSAGE)
+		factory->message->data.heap_frag = bp;
             factory->mode = FACTORY_CLOSED;
             return;
         }
-        /*else we don't trim multi fragmented messages for now */
+        /*else we don't trim multi fragmented messages for now (off_heap...) */
+    default:
+	break;
     }
     erts_factory_close(factory);
 }
@@ -1349,38 +1683,35 @@ void erts_factory_undo(ErtsHeapFactory* factory)
 
             /* Rollback heap top
 	     */
-            if (factory->heap_frags_saved == NULL) { /* No heap frags when we started */
-                ASSERT(factory->hp_start >= HEAP_START(factory->p));
-                ASSERT(factory->hp_start <= HEAP_LIMIT(factory->p));
 
-                HEAP_TOP(factory->p) = factory->hp_start;
-            }
-            else {
+	    if (HEAP_START(factory->p) <= factory->hp_start
+		&& factory->hp_start <= HEAP_LIMIT(factory->p)) {
+		HEAP_TOP(factory->p) = factory->hp_start;
+	    }
+
+	    /* Fix last heap frag */
+            if (factory->heap_frags_saved) {
                 ASSERT(factory->heap_frags_saved == factory->p->mbuf);
-                if (factory->hp_start == factory->heap_frags_saved->mem) {
+                if (factory->hp_start != factory->heap_frags_saved->mem)
+                    factory->heap_frags_saved->used_size = factory->heap_frags_saved_used;
+		else {
                     factory->p->mbuf = factory->p->mbuf->next;
                     ERTS_HEAP_FREE(ERTS_ALC_T_HEAP_FRAG, factory->heap_frags_saved,
                                    ERTS_HEAP_FRAG_SIZE(factory->heap_frags_saved->alloc_size));
                 }
-                else if (factory->hp_start != factory->hp_end) {
-                    unsigned remains = factory->hp_start - factory->heap_frags_saved->mem;
-                    ASSERT(remains > 0 && remains < factory->heap_frags_saved->used_size);
-                    factory->heap_frags_saved->used_size = remains;
-                }
             }
         }
         break;
 
+    case FACTORY_MESSAGE:
+	if (factory->message->data.attached == ERTS_MSG_COMBINED_HFRAG)
+	    factory->message->hfrag.next = factory->heap_frags;
+	else
+	    factory->message->data.heap_frag = factory->heap_frags;
+	erts_cleanup_messages(factory->message);
+	break;
     case FACTORY_HEAP_FRAGS:
-        bp = factory->heap_frags;
-        do {
-            ErlHeapFragment* next_bp = bp->next;
-
-            erts_cleanup_offheap(&bp->off_heap);
-            ERTS_HEAP_FREE(factory->alloc_type, (void *) bp,
-                           ERTS_HEAP_FRAG_SIZE(bp->size));
-            bp = next_bp;
-        }while (bp != NULL);
+	free_message_buffer(factory->heap_frags);
 	break;
 
     case FACTORY_CLOSED: break;