Add a persistent term storage

Persistent terms are useful for storing Erlang terms that are never
or infrequently updated. They have the following advantages:

* Constant time access. A persistent term is not copied when it is
  looked up. The constant factor is lower than for ETS, and no locks
  are taken when looking up a term.

* Persistent terms are not copied in garbage collections.

* There is only ever one copy of a persistent term (until it is
  deleted). That makes them useful for storing configuration data
  that needs to be easily accessible by all processes.

Persistent terms have the following drawbacks:

* Updates are expensive. The hash table holding the keys for the
  persistent terms are updated whenever a persistent term is added,
  updated or deleted.

* Updating or deleting a persistent term triggers a "global GC", which
  will schedule a heap scan of all processes to search the heap of all
  processes for the deleted term. If a process still holds a reference
  to the deleted term, the process will be garbage collected and the
  term copied to the heap of the process. This global GC can make the
  system less responsive for some time.

Three BIFs (implemented in C in the emulator) is the entire
interface to the persistent term functionality:

* put(Key, Value) to store a persistent term.

* get(Key) to look up a persistent term.

* erase(Key) to delete a persistent term.

There are also two additional BIFs to obtain information about
persistent terms:

* info() to return a map with information about persistent terms.

* get() to return a list of a {Key,Value} tuples for all persistent
  terms. (The values are not copied.)

22 files changed, 2039 insertions, 18 deletions

diff --git a/erts/doc/src/Makefile b/erts/doc/src/Makefile
index 21aa3db864..fccdd744f3 100644
--- a/erts/doc/src/Makefile
+++ b/erts/doc/src/Makefile
@@ -52,6 +52,7 @@ XML_REF3_EFILES = \
 	erlang.xml \
 	erl_tracer.xml \
 	init.xml \
+	persistent_term.xml \
 	zlib.xml
 
 XML_REF3_FILES = \
@@ -63,6 +64,7 @@ XML_REF3_FILES = \
 	erlang.xml \
 	erts_alloc.xml  \
 	init.xml \
+	persistent_term.xml \
 	zlib.xml
 
 XML_PART_FILES = \
diff --git a/erts/doc/src/persistent_term.xml b/erts/doc/src/persistent_term.xml
new file mode 100644
index 0000000000..d2a138d65f
--- /dev/null
+++ b/erts/doc/src/persistent_term.xml
@@ -0,0 +1,290 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<!DOCTYPE erlref SYSTEM "erlref.dtd">
+
+<erlref>
+  <header>
+    <copyright>
+      <year>2018</year><year>2018</year>
+      <holder>Ericsson AB. All Rights Reserved.</holder>
+    </copyright>
+    <legalnotice>
+      Licensed under the Apache License, Version 2.0 (the "License");
+      you may not use this file except in compliance with the License.
+      You may obtain a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+      Unless required by applicable law or agreed to in writing, software
+      distributed under the License is distributed on an "AS IS" BASIS,
+      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+      See the License for the specific language governing permissions and
+      limitations under the License.
+
+    </legalnotice>
+
+    <title>persistent_term</title>
+    <prepared></prepared>
+    <docno></docno>
+    <date></date>
+    <rev></rev>
+    <file>persistent_term.xml</file>
+  </header>
+  <module>persistent_term</module>
+  <modulesummary>Persistent terms.</modulesummary>
+  <description>
+    <p>This module is similar to <seealso
+    marker="stdlib:ets"><c>ets</c></seealso> in that it provides a
+    storage for Erlang terms that can be accessed in constant time,
+    but with the difference that <c>persistent_term</c> has been
+    highly optimized for reading terms at the expense of writing and
+    updating terms. When a persistent term is updated or deleted, a
+    global garbage collection pass is run to scan all processes for
+    the deleted term, and to copy it into each process that still uses
+    it. Therefore, <c>persistent_term</c> is suitable for storing
+    Erlang terms that are frequently accessed but never or
+    infrequently updated.</p>
+
+    <warning><p>Persistent terms is an advanced feature and is not a
+    general replacement for ETS tables. Before using persistent terms,
+    make sure to fully understand the consequence to system
+    performance when updating or deleting persistent terms.</p></warning>
+
+    <p>Term lookup (using <seealso
+    marker="#get/1"><c>get/1</c></seealso>), is done in constant time
+    and without taking any locks, and the term is <strong>not</strong>
+    copied to the heap (as is the case with terms stored in ETS
+    tables).</p>
+
+    <p>Storing or updating a term (using <seealso
+    marker="#put/2"><c>put/2</c></seealso>) is proportional to the
+    number of already created persistent terms because the hash table
+    holding the keys will be copied. In addition, the term itself will
+    be copied.</p>
+
+    <p>When a (complex) term is deleted (using <seealso
+    marker="#erase/1"><c>erase/1</c></seealso>) or replaced by another
+    (using <seealso marker="#put/2"><c>put/2</c></seealso>), a global
+    garbage collection is initiated. It works like this:</p>
+
+    <list>
+      <item><p>All processes in the system will be scheduled to run a
+      scan of their heaps for the term that has been deleted.  While
+      such scan is relatively light-weight, if there are many
+      processes, the system can become less responsive until all
+      process have scanned theirs heaps.</p></item>
+
+      <item><p>If the deleted term (or any part of it) is still used
+      by a process, that process will do a major (fullsweep) garbage
+      collection and copy the term into the process. However, at most
+      two processes at a time will be scheduled to do that kind of
+      garbage collection.</p></item>
+    </list>
+
+    <p>Deletion of atoms and other terms that fit in one machine word
+    is specially optimized to avoid doing a global GC. It is still not
+    recommended to update persistent terms with such values too
+    frequently because the hash table holding the keys is copied every
+    time a persistent term is updated.</p>
+
+    <p>Some examples are suitable uses for persistent terms are:</p>
+
+    <list>
+      <item><p>Storing of configuration data that must be easily
+      accessible by all processes.</p></item>
+
+      <item><p>Storing of references for NIF resources.</p></item>
+
+      <item><p>Storing of references for efficient counters.</p></item>
+
+      <item><p>Storing an atom to indicate a logging level or whether debugging
+      is turned on.</p></item>
+    </list>
+
+  </description>
+
+  <section>
+    <title>Storing Huge Persistent Terms</title>
+    <p>The current implementation of persistent terms uses the literal
+    <seealso marker="erts_alloc">allocator</seealso> also used for
+    literals (constant terms) in BEAM code.  By default, 1 GB of
+    virtual address space is reserved for literals in BEAM code and
+    persistent terms. The amount of virtual address space reserved for
+    literals can be changed by using the <seealso
+    marker="erts_alloc#MIscs"><c>+MIscs option</c></seealso> when
+    starting the emulator.</p>
+
+    <p>Here is an example how the reserved virtual address space for literals
+    can be raised to 2 GB (2048 MB):</p>
+
+    <pre>
+    erl +MIscs 2048</pre>
+  </section>
+
+  <section>
+    <title>Warning For Many Persistent Terms</title>
+    <p>The runtime system will send a warning report to the
+    error logger if more than 20000 persistent terms have been
+    created. It will look like this:</p>
+
+<pre>
+More than 20000 persistent terms have been created.
+It is recommended to avoid creating an excessive number of
+persistent terms, as creation and deletion of persistent terms
+will be slower as the number of persistent terms increases.</pre>
+  </section>
+
+  <section>
+    <title>Best Practices for Using Persistent Terms</title>
+
+    <p>It is recommended to use keys like <c>?MODULE</c> or
+    <c>{?MODULE,SubKey}</c> to avoid name collisions.</p>
+
+    <p>Prefer creating a few large persistent terms to creating many
+    small persistent terms. The execution time for storing a
+    persistent term is proportional to the number of already existing
+    terms.</p>
+
+    <p>Updating a persistent term with the same value as it already
+    has is specially optimized to do nothing quickly; thus, there is
+    no need compare the old and new values and avoid calling
+    <seealso marker="#put/2"><c>put/2</c></seealso> if the values
+    are equal.</p>
+
+    <p>When atoms or other terms that fit in one machine word are
+    deleted, no global GC is needed. Therefore, persistent terms that
+    have atoms as their values can be updated more frequently, but
+    note that updating such persistent terms is still much more
+    expensive than reading them.</p>
+
+    <p>Updating or deleting a persistent term will trigger a global GC
+    if the term does not fit in one machine word. Processes will be
+    scheduled as usual, but all processes will be made runnable at
+    once, which will make the system less responsive until all process
+    have run and scanned their heaps for the deleted terms. One way to
+    minimize the effects on responsiveness could be to minimize the
+    number of processes on the node before updating or deleting a
+    persistent term. It would also be wise to avoid updating terms
+    when the system is at peak load.</p>
+
+    <p>Avoid storing a retrieved persistent term in a process if that
+    persistent term could be deleted or updated in the future. If a
+    process holds a reference to a persistent term when the term is
+    deleted, the process will be garbage collected and the term copied
+    to process.</p>
+
+    <p>Avoid updating or deleting more than one persistent term at a
+    time.  Each deleted term will trigger its own global GC. That
+    means that deleting N terms will make the system less responsive N
+    times longer than deleting a single persistent term. Therefore,
+    terms that are to be updated at the same time should be collected
+    into a larger term, for example, a map or a tuple.</p>
+  </section>
+
+  <section>
+    <title>Example</title>
+
+    <p>The following example shows how lock contention for ETS tables
+    can be minimized by having one ETS table for each scheduler. The
+    table identifiers for the ETS tables are stored as a single
+    persistent term:</p>
+
+<pre>
+    %% There is one ETS table for each scheduler.
+    Sid = erlang:system_info(scheduler_id),
+    Tid = element(Sid, persistent_term:get(?MODULE)),
+    ets:update_counter(Tid, Key, 1).</pre>
+
+  </section>
+
+  <datatypes>
+    <datatype>
+      <name name="key"/>
+      <desc>
+        <p>Any Erlang term.</p>
+      </desc>
+    </datatype>
+    <datatype>
+      <name name="value"/>
+      <desc>
+        <p>Any Erlang term.</p>
+      </desc>
+    </datatype>
+  </datatypes>
+
+  <funcs>
+    <func>
+      <name name="erase" arity="1"/>
+      <fsummary>Erase the name for a persistent term.</fsummary>
+      <desc>
+        <p>Erase the name for the persistent term with key
+	<c><anno>Key</anno></c>. The return value will be <c>true</c>
+	if there was a persistent term with the key
+	<c><anno>Key</anno></c>, and <c>false</c> if there was no
+	persistent term associated with the key.</p>
+	<p>If there existed a previous persistent term associated with
+	key <c><anno>Key</anno></c>, a global GC has been initiated
+	when <c>erase/1</c> returns. See <seealso
+	marker="#description">Description</seealso>.</p>
+      </desc>
+    </func>
+
+    <func>
+      <name name="get" arity="0"/>
+      <fsummary>Get all persistent terms.</fsummary>
+      <desc>
+        <p>Retrieve the keys and values for all persistent terms.
+	The keys will be copied to the heap for the process calling
+	<c>get/0</c>, but the values will not.</p>
+      </desc>
+    </func>
+
+    <func>
+      <name name="get" arity="1"/>
+      <fsummary>Get the value for a persistent term.</fsummary>
+      <desc>
+        <p>Retrieve the value for the persistent term associated with
+        the key <c><anno>Key</anno></c>. The lookup will be made in
+	constant time and the value will not be copied to the heap
+	of the calling process.</p>
+	<p>This function fails with a <c>badarg</c> exception if no
+	term has been stored with the key
+	<c><anno>Key</anno></c>.</p>
+	<p>If the calling process holds on to the value of the
+	persistent term and the persistent term is deleted in the future,
+	the term will be copied to the process.</p>
+      </desc>
+    </func>
+
+    <func>
+      <name name="info" arity="0"/>
+      <fsummary>Get information about persistent terms.</fsummary>
+      <desc>
+        <p>Return information about persistent terms in a map. The map
+	has the following keys:</p>
+	<taglist>
+	  <tag><c>count</c></tag>
+	  <item><p>The number of persistent terms.</p></item>
+	  <tag><c>memory</c></tag>
+	  <item><p>The total amount of memory (measured in bytes)
+	  used by all persistent terms.</p></item>
+	</taglist>
+      </desc>
+    </func>
+
+    <func>
+      <name name="put" arity="2"/>
+      <fsummary>Store a term.</fsummary>
+      <desc>
+        <p>Store the value <c><anno>Value</anno></c> as a persistent term and
+	associate it with the key <c><anno>Key</anno></c>.</p>
+	<p>If the value <c><anno>Value</anno></c> is equal to the value
+	previously stored for the key, <c>put/2</c> will do nothing and return
+	quickly.</p>
+	<p>If there existed a previous persistent term associated with
+	key <c><anno>Key</anno></c>, a global GC has been initiated
+	when <c>put/2</c> returns. See <seealso
+	marker="#description">Description</seealso>.</p>
+      </desc>
+    </func>
+  </funcs>
+</erlref>
diff --git a/erts/doc/src/ref_man.xml b/erts/doc/src/ref_man.xml
index 0617463a7b..ff64aa86b8 100644
--- a/erts/doc/src/ref_man.xml
+++ b/erts/doc/src/ref_man.xml
@@ -34,6 +34,7 @@
   <xi:include href="erl_prim_loader.xml"/>
   <xi:include href="erlang.xml"/>
   <xi:include href="init.xml"/>
+  <xi:include href="persistent_term.xml"/>
   <xi:include href="zlib.xml"/>
   <xi:include href="epmd.xml"/>
   <xi:include href="erl.xml"/>
diff --git a/erts/doc/src/specs.xml b/erts/doc/src/specs.xml
index ed6be650e5..1ab6cdc19e 100644
--- a/erts/doc/src/specs.xml
+++ b/erts/doc/src/specs.xml
@@ -4,5 +4,6 @@
   <xi:include href="../specs/specs_erlang.xml"/>
   <xi:include href="../specs/specs_erl_tracer.xml"/>
   <xi:include href="../specs/specs_init.xml"/>
+  <xi:include href="../specs/specs_persistent_term.xml"/>
   <xi:include href="../specs/specs_zlib.xml"/>
 </specs>
diff --git a/erts/emulator/Makefile.in b/erts/emulator/Makefile.in
index 054692819e..d5ceb4b00b 100644
--- a/erts/emulator/Makefile.in
+++ b/erts/emulator/Makefile.in
@@ -633,21 +633,22 @@ GENERATE += $(TTF_DIR)/driver_tab.c
 # This list must be consistent with PRE_LOADED_MODULES in
 # erts/preloaded/src/Makefile.
 
-PRELOAD_BEAM =		$(ERL_TOP)/erts/preloaded/ebin/otp_ring0.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/erts_code_purger.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/init.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/prim_buffer.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/prim_eval.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/prim_inet.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/prim_file.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/zlib.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/prim_zip.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/erl_prim_loader.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/erlang.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/erts_internal.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/erl_tracer.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/erts_literal_area_collector.beam \
-			$(ERL_TOP)/erts/preloaded/ebin/erts_dirty_process_signal_handler.beam
+PRELOAD_BEAM =	$(ERL_TOP)/erts/preloaded/ebin/otp_ring0.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/erts_code_purger.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/init.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/prim_buffer.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/prim_eval.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/prim_inet.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/prim_file.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/zlib.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/prim_zip.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/erl_prim_loader.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/erlang.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/erts_internal.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/erl_tracer.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/erts_literal_area_collector.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/erts_dirty_process_signal_handler.beam \
+		$(ERL_TOP)/erts/preloaded/ebin/persistent_term.beam
 
 ifeq ($(TARGET),win32)
 # On windows the preloaded objects are in a resource object.
@@ -839,6 +840,7 @@ RUN_OBJS += \
 	$(OBJDIR)/erl_bif_ddll.o  	$(OBJDIR)/erl_bif_guard.o \
 	$(OBJDIR)/erl_bif_info.o	$(OBJDIR)/erl_bif_op.o \
 	$(OBJDIR)/erl_bif_os.o		$(OBJDIR)/erl_bif_lists.o \
+	$(OBJDIR)/erl_bif_persistent.o \
 	$(OBJDIR)/erl_bif_trace.o	$(OBJDIR)/erl_bif_unique.o \
 	$(OBJDIR)/erl_bif_wrap.o	$(OBJDIR)/erl_nfunc_sched.o \
 	$(OBJDIR)/erl_guard_bifs.o 	$(OBJDIR)/erl_dirty_bif_wrap.o \
diff --git a/erts/emulator/beam/atom.names b/erts/emulator/beam/atom.names
index 45b7540aeb..82bb620d62 100644
--- a/erts/emulator/beam/atom.names
+++ b/erts/emulator/beam/atom.names
@@ -182,6 +182,7 @@ atom control
 atom copy
 atom copy_literals
 atom counters
+atom count
 atom cpu
 atom cpu_timestamp
 atom cr
@@ -287,6 +288,7 @@ atom gc_minor_end
 atom gc_minor_start
 atom Ge='>='
 atom generational
+atom get_all_trap
 atom get_seq_token
 atom get_tcw
 atom gather_gc_info_result
@@ -325,6 +327,7 @@ atom index
 atom infinity
 atom info
 atom info_msg
+atom info_trap
 atom init
 atom initial_call
 atom input
diff --git a/erts/emulator/beam/bif.tab b/erts/emulator/beam/bif.tab
index 7548924178..f1f34ae323 100644
--- a/erts/emulator/beam/bif.tab
+++ b/erts/emulator/beam/bif.tab
@@ -40,6 +40,7 @@
 # Note: Guards BIFs usually require special support in the compiler.
 #
 
+
 gcbif erlang:abs/1
 bif erlang:adler32/1
 bif erlang:adler32/2
@@ -698,3 +699,14 @@ ubif erlang:map_get/2
 ubif erlang:is_map_key/2
 bif ets:internal_delete_all/2
 bif ets:internal_select_delete/2
+
+#
+# New in 21.2
+#
+
+bif persistent_term:put/2
+bif persistent_term:get/1
+bif persistent_term:get/0
+bif persistent_term:erase/1
+bif persistent_term:info/0
+bif erts_internal:erase_persistent_terms/0
diff --git a/erts/emulator/beam/erl_alloc.types b/erts/emulator/beam/erl_alloc.types
index 5409b89bab..86d93d94c4 100644
--- a/erts/emulator/beam/erl_alloc.types
+++ b/erts/emulator/beam/erl_alloc.types
@@ -277,6 +277,9 @@ type	SETUP_CONN_ARG	SHORT_LIVED	PROCESSES	setup_connection_argument
 
 type	ENVIRONMENT	SYSTEM		SYSTEM		environment
 
+type	PERSISTENT_TERM	LONG_LIVED	CODE		persisten_term
+type	PERSISTENT_LOCK_Q SHORT_LIVED	SYSTEM		persistent_lock_q
+
 #
 # Types used for special emulators
 #
diff --git a/erts/emulator/beam/erl_bif_persistent.c b/erts/emulator/beam/erl_bif_persistent.c
new file mode 100644
index 0000000000..9dca768a18
--- /dev/null
+++ b/erts/emulator/beam/erl_bif_persistent.c
@@ -0,0 +1,983 @@
+/*
+ * %CopyrightBegin%
+ *
+ * Copyright Ericsson AB 2018. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * %CopyrightEnd%
+ */
+
+/*
+ * Purpose: Implement persistent term storage.
+ */
+
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif
+
+#include "sys.h"
+#include "erl_vm.h"
+#include "global.h"
+#include "erl_process.h"
+#include "error.h"
+#include "erl_driver.h"
+#include "bif.h"
+#include "erl_map.h"
+#include "erl_binary.h"
+
+/*
+ * The limit for the number of persistent terms before
+ * a warning is issued.
+ */
+
+#define WARNING_LIMIT 20000
+#define XSTR(s) STR(s)
+#define STR(s) #s
+
+/*
+ * Parameters for the hash table.
+ */
+#define INITIAL_SIZE 8
+#define LOAD_FACTOR ((Uint)50)
+#define MUST_GROW(t) (((Uint)100) * t->num_entries >= LOAD_FACTOR * t->allocated)
+#define MUST_SHRINK(t) (((Uint)200) * t->num_entries <= LOAD_FACTOR * t->allocated && \
+                        t->allocated > INITIAL_SIZE)
+
+typedef struct hash_table {
+    Uint allocated;
+    Uint num_entries;
+    Uint mask;
+    Uint first_to_delete;
+    Uint num_to_delete;
+    erts_atomic_t refc;
+    struct hash_table* delete_next;
+    ErtsThrPrgrLaterOp thr_prog_op;
+    Eterm term[1];
+} HashTable;
+
+typedef struct trap_data {
+    HashTable* table;
+    Uint idx;
+    Uint remaining;
+    Uint memory;    /* Used by info/0 to count used memory */
+} TrapData;
+
+/*
+ * Declarations of local functions.
+ */
+
+static HashTable* create_initial_table(void);
+static Uint lookup(HashTable* hash_table, Eterm key);
+static HashTable* copy_table(HashTable* old_table, Uint new_size, int rehash);
+static HashTable* tmp_table_copy(HashTable* old_table);
+static int try_seize_update_permission(Process* c_p);
+static void release_update_permission(int release_updater);
+static void table_updater(void* table);
+static void table_deleter(void* hash_table);
+static void dec_table_refc(Process* c_p, HashTable* old_table);
+static void delete_table(Process* c_p, HashTable* table);
+static void mark_for_deletion(HashTable* hash_table, Uint entry_index);
+static ErtsLiteralArea* term_to_area(Eterm tuple);
+static void suspend_updater(Process* c_p);
+static Eterm do_get_all(Process* c_p, TrapData* trap_data, Eterm res);
+static Eterm do_info(Process* c_p, TrapData* trap_data);
+static void append_to_delete_queue(HashTable* table);
+static HashTable* next_to_delete(void);
+static Eterm alloc_trap_data(Process* c_p);
+static int cleanup_trap_data(Binary *bp);
+
+/*
+ * Traps
+ */
+
+static Export persistent_term_get_all_export;
+static BIF_RETTYPE persistent_term_get_all_trap(BIF_ALIST_2);
+static Export persistent_term_info_export;
+static BIF_RETTYPE persistent_term_info_trap(BIF_ALIST_1);
+
+/*
+ * Pointer to the current hash table.
+ */
+
+static erts_atomic_t the_hash_table;
+
+/*
+ * Queue of processes waiting to update the hash table.
+ */
+
+struct update_queue_item {
+    Process *p;
+    struct update_queue_item* next;
+};
+
+static erts_mtx_t update_table_permission_mtx;
+static struct update_queue_item* update_queue = NULL;
+static Process* updater_process = NULL;
+
+/* Protected by update_table_permission_mtx */
+static ErtsThrPrgrLaterOp thr_prog_op;
+static int issued_warning = 0;
+
+/*
+ * Queue of hash tables to be deleted.
+ */
+
+static erts_mtx_t delete_queue_mtx;
+static HashTable* delete_queue_head = NULL;
+static HashTable** delete_queue_tail = &delete_queue_head;
+
+/*
+ * The following variables are only used during crash dumping. They
+ * are intialized by erts_init_persistent_dumping().
+ */
+
+ErtsLiteralArea** erts_persistent_areas;
+Uint erts_num_persistent_areas;
+
+void erts_init_bif_persistent_term(void)
+{
+    HashTable* hash_table;
+
+    /*
+     * Initialize the mutex protecting updates.
+     */
+
+    erts_mtx_init(&update_table_permission_mtx,
+                  "update_persistent_term_permission",
+                  NIL,
+                  ERTS_LOCK_FLAGS_PROPERTY_STATIC |
+                  ERTS_LOCK_FLAGS_CATEGORY_GENERIC);
+
+    /*
+     * Initialize delete queue.
+     */
+
+    erts_mtx_init(&delete_queue_mtx,
+                  "persistent_term_delete_permission",
+                  NIL,
+                  ERTS_LOCK_FLAGS_PROPERTY_STATIC |
+                  ERTS_LOCK_FLAGS_CATEGORY_GENERIC);
+
+    /*
+     * Allocate a small initial hash table.
+     */
+
+    hash_table = create_initial_table();
+    erts_atomic_init_nob(&the_hash_table, (erts_aint_t)hash_table);
+
+    /*
+     * Initialize export entry for traps
+     */
+
+    erts_init_trap_export(&persistent_term_get_all_export,
+			  am_persistent_term, am_get_all_trap, 2,
+			  &persistent_term_get_all_trap);
+    erts_init_trap_export(&persistent_term_info_export,
+			  am_persistent_term, am_info_trap, 1,
+			  &persistent_term_info_trap);
+}
+
+BIF_RETTYPE persistent_term_put_2(BIF_ALIST_2)
+{
+    Eterm key;
+    Eterm term;
+    Eterm heap[3];
+    Eterm tuple;
+    HashTable* hash_table;
+    Uint term_size;
+    Uint lit_area_size;
+    ErlOffHeap code_off_heap;
+    ErtsLiteralArea* literal_area;
+    erts_shcopy_t info;
+    Eterm* ptr;
+    Uint entry_index;
+
+    if (!try_seize_update_permission(BIF_P)) {
+	ERTS_BIF_YIELD2(bif_export[BIF_persistent_term_put_2],
+                        BIF_P, BIF_ARG_1, BIF_ARG_2);
+    }
+
+    hash_table = (HashTable *) erts_atomic_read_nob(&the_hash_table);
+
+    key = BIF_ARG_1;
+    term = BIF_ARG_2;
+
+    entry_index = lookup(hash_table, key);
+
+    heap[0] = make_arityval(2);
+    heap[1] = key;
+    heap[2] = term;
+    tuple = make_tuple(heap);
+
+    if (is_nil(hash_table->term[entry_index])) {
+        Uint size = hash_table->allocated;
+        if (MUST_GROW(hash_table)) {
+            size *= 2;
+        }
+        hash_table = copy_table(hash_table, size, 0);
+        entry_index = lookup(hash_table, key);
+        hash_table->num_entries++;
+    } else {
+        Eterm tuple = hash_table->term[entry_index];
+        Eterm old_term;
+
+        ASSERT(is_tuple_arity(tuple, 2));
+        old_term = boxed_val(tuple)[2];
+        if (EQ(term, old_term)) {
+            /* Same value. No need to update anything. */
+            release_update_permission(0);
+            BIF_RET(am_ok);
+        } else {
+            /* Mark the old term for deletion. */
+            mark_for_deletion(hash_table, entry_index);
+            hash_table = copy_table(hash_table, hash_table->allocated, 0);
+        }
+    }
+
+    /*
+     * Preserve internal sharing in the term by using the
+     * sharing-preserving functions. However, literals must
+     * be copied in case the module holding them are unloaded.
+     */
+    INITIALIZE_SHCOPY(info);
+    info.copy_literals = 1;
+    term_size = copy_shared_calculate(tuple, &info);
+    ERTS_INIT_OFF_HEAP(&code_off_heap);
+    lit_area_size = ERTS_LITERAL_AREA_ALLOC_SIZE(term_size);
+    literal_area = erts_alloc(ERTS_ALC_T_LITERAL, lit_area_size);
+    ptr = &literal_area->start[0];
+    literal_area->end = ptr + term_size;
+    tuple = copy_shared_perform(tuple, term_size, &info, &ptr, &code_off_heap);
+    ASSERT(tuple_val(tuple) == literal_area->start);
+    literal_area->off_heap = code_off_heap.first;
+    DESTROY_SHCOPY(info);
+    erts_set_literal_tag(&tuple, literal_area->start, term_size);
+    hash_table->term[entry_index] = tuple;
+
+    erts_schedule_thr_prgr_later_op(table_updater, hash_table, &thr_prog_op);
+    suspend_updater(BIF_P);
+
+    /*
+     * Issue a warning once if the warning limit has been exceeded.
+     */
+
+    if (hash_table->num_entries > WARNING_LIMIT && issued_warning == 0) {
+        static char w[] =
+            "More than " XSTR(WARNING_LIMIT) " persistent terms "
+            "have been created.\n"
+            "It is recommended to avoid creating an excessive number of\n"
+            "persistent terms, as creation and deletion of persistent terms\n"
+            "will be slower as the number of persistent terms increases.\n";
+        issued_warning = 1;
+	erts_send_warning_to_logger_str(BIF_P->group_leader, w);
+    }
+
+    ERTS_BIF_YIELD_RETURN(BIF_P, am_ok);
+}
+
+BIF_RETTYPE persistent_term_get_0(BIF_ALIST_0)
+{
+    HashTable* hash_table = (HashTable *) erts_atomic_read_nob(&the_hash_table);
+    TrapData* trap_data;
+    Eterm res = NIL;
+    Eterm magic_ref;
+    Binary* mbp;
+
+    magic_ref = alloc_trap_data(BIF_P);
+    mbp = erts_magic_ref2bin(magic_ref);
+    trap_data = ERTS_MAGIC_BIN_DATA(mbp);
+    trap_data->table = hash_table;
+    trap_data->idx = 0;
+    trap_data->remaining = hash_table->num_entries;
+    res = do_get_all(BIF_P, trap_data, res);
+    if (trap_data->remaining == 0) {
+        BUMP_REDS(BIF_P, hash_table->num_entries);
+        trap_data->table = NULL; /* Prevent refc decrement */
+        BIF_RET(res);
+    } else {
+        /*
+         * Increment the ref counter to prevent an update operation (by put/2
+         * or erase/1) to delete this hash table.
+         */
+        erts_atomic_inc_nob(&hash_table->refc);
+        BUMP_ALL_REDS(BIF_P);
+        BIF_TRAP2(&persistent_term_get_all_export, BIF_P, magic_ref, res);
+    }
+}
+
+BIF_RETTYPE persistent_term_get_1(BIF_ALIST_1)
+{
+    Eterm key = BIF_ARG_1;
+    HashTable* hash_table = (HashTable *) erts_atomic_read_nob(&the_hash_table);
+    Uint entry_index;
+    Eterm term;
+
+    entry_index = lookup(hash_table, key);
+    term = hash_table->term[entry_index];
+    if (is_boxed(term)) {
+        ASSERT(is_tuple_arity(term, 2));
+        BIF_RET(tuple_val(term)[2]);
+    }
+    BIF_ERROR(BIF_P, BADARG);
+}
+
+BIF_RETTYPE persistent_term_erase_1(BIF_ALIST_1)
+{
+    Eterm key = BIF_ARG_1;
+    HashTable* old_table;
+    HashTable* new_table;
+    Uint entry_index;
+    Eterm old_term;
+
+    if (!try_seize_update_permission(BIF_P)) {
+	ERTS_BIF_YIELD1(bif_export[BIF_persistent_term_erase_1],
+                        BIF_P, BIF_ARG_1);
+    }
+
+    old_table = (HashTable *) erts_atomic_read_nob(&the_hash_table);
+    entry_index = lookup(old_table, key);
+    old_term = old_table->term[entry_index];
+    if (is_boxed(old_term)) {
+        Uint new_size;
+        HashTable* tmp_table;
+
+        /*
+         * Since we don't use any delete markers, we must rehash
+         * the table when deleting terms to ensure that all terms
+         * can still be reached if there are hash collisions.
+         * We can't rehash in place and it would not be safe to modify
+         * the old table yet, so we will first need a new
+         * temporary table copy of the same size as the old one.
+         */
+
+        ASSERT(is_tuple_arity(old_term, 2));
+        tmp_table = tmp_table_copy(old_table);
+
+        /*
+         * Delete the term from the temporary table. Then copy the
+         * temporary table to a new table, rehashing the entries
+         * while copying.
+         */
+
+        tmp_table->term[entry_index] = NIL;
+        tmp_table->num_entries--;
+        new_size = tmp_table->allocated;
+        if (MUST_SHRINK(tmp_table)) {
+            new_size /= 2;
+        }
+        new_table = copy_table(tmp_table, new_size, 1);
+        erts_free(ERTS_ALC_T_TMP, tmp_table);
+
+        mark_for_deletion(old_table, entry_index);
+        erts_schedule_thr_prgr_later_op(table_updater, new_table, &thr_prog_op);
+        suspend_updater(BIF_P);
+        ERTS_BIF_YIELD_RETURN(BIF_P, am_true);
+    }
+
+    /*
+     * Key is not present. Nothing to do.
+     */
+
+    ASSERT(is_nil(old_term));
+    release_update_permission(0);
+    BIF_RET(am_false);
+}
+
+BIF_RETTYPE erts_internal_erase_persistent_terms_0(BIF_ALIST_0)
+{
+    HashTable* old_table;
+    HashTable* new_table;
+
+    if (!try_seize_update_permission(BIF_P)) {
+	ERTS_BIF_YIELD0(bif_export[BIF_erts_internal_erase_persistent_terms_0],
+                        BIF_P);
+    }
+    old_table = (HashTable *) erts_atomic_read_nob(&the_hash_table);
+    old_table->first_to_delete = 0;
+    old_table->num_to_delete = old_table->allocated;
+    new_table = create_initial_table();
+    erts_schedule_thr_prgr_later_op(table_updater, new_table, &thr_prog_op);
+    suspend_updater(BIF_P);
+    ERTS_BIF_YIELD_RETURN(BIF_P, am_true);
+}
+
+BIF_RETTYPE persistent_term_info_0(BIF_ALIST_0)
+{
+    HashTable* hash_table = (HashTable *) erts_atomic_read_nob(&the_hash_table);
+    TrapData* trap_data;
+    Eterm res = NIL;
+    Eterm magic_ref;
+    Binary* mbp;
+
+    magic_ref = alloc_trap_data(BIF_P);
+    mbp = erts_magic_ref2bin(magic_ref);
+    trap_data = ERTS_MAGIC_BIN_DATA(mbp);
+    trap_data->table = hash_table;
+    trap_data->idx = 0;
+    trap_data->remaining = hash_table->num_entries;
+    trap_data->memory = 0;
+    res = do_info(BIF_P, trap_data);
+    if (trap_data->remaining == 0) {
+        BUMP_REDS(BIF_P, hash_table->num_entries);
+        trap_data->table = NULL; /* Prevent refc decrement */
+        BIF_RET(res);
+    } else {
+        /*
+         * Increment the ref counter to prevent an update operation (by put/2
+         * or erase/1) to delete this hash table.
+         */
+        erts_atomic_inc_nob(&hash_table->refc);
+        BUMP_ALL_REDS(BIF_P);
+        BIF_TRAP2(&persistent_term_info_export, BIF_P, magic_ref, res);
+    }
+}
+
+Uint
+erts_persistent_term_count(void)
+{
+    HashTable* hash_table = (HashTable *) erts_atomic_read_nob(&the_hash_table);
+    return hash_table->num_entries;
+}
+
+void
+erts_init_persistent_dumping(void)
+{
+    HashTable* hash_table = (HashTable *) erts_atomic_read_nob(&the_hash_table);
+    ErtsLiteralArea** area_p;
+    Uint i;
+
+    /*
+     * Overwrite the array of Eterms in the current hash table
+     * with pointers to literal areas.
+     */
+
+    erts_persistent_areas = (ErtsLiteralArea **) hash_table->term;
+    erts_num_persistent_areas = hash_table->num_entries;
+    area_p = erts_persistent_areas;
+    for (i = 0; i < hash_table->allocated; i++) {
+        Eterm term = hash_table->term[i];
+
+        if (is_boxed(term)) {
+            *area_p++ = term_to_area(term);
+        }
+    }
+}
+
+/*
+ * Local functions.
+ */
+
+static HashTable*
+create_initial_table(void)
+{
+    HashTable* hash_table;
+    int i;
+
+    hash_table = (HashTable *) erts_alloc(ERTS_ALC_T_PERSISTENT_TERM,
+                                          sizeof(HashTable)+sizeof(Eterm) *
+                                          (INITIAL_SIZE-1));
+    hash_table->allocated = INITIAL_SIZE;
+    hash_table->num_entries = 0;
+    hash_table->mask = INITIAL_SIZE-1;
+    hash_table->first_to_delete = 0;
+    hash_table->num_to_delete = 0;
+    erts_atomic_init_nob(&hash_table->refc, (erts_aint_t)1);
+    for (i = 0; i < INITIAL_SIZE; i++) {
+        hash_table->term[i] = NIL;
+    }
+    return hash_table;
+}
+
+static BIF_RETTYPE
+persistent_term_get_all_trap(BIF_ALIST_2)
+{
+    TrapData* trap_data;
+    Eterm res = BIF_ARG_2;
+    Uint bump_reds;
+    Binary* mbp;
+
+    ASSERT(is_list(BIF_ARG_2));
+    mbp = erts_magic_ref2bin(BIF_ARG_1);
+    trap_data = ERTS_MAGIC_BIN_DATA(mbp);
+    bump_reds = trap_data->remaining;
+    res = do_get_all(BIF_P, trap_data, res);
+    ASSERT(is_list(res));
+    if (trap_data->remaining > 0) {
+        BUMP_ALL_REDS(BIF_P);
+        BIF_TRAP2(&persistent_term_get_all_export, BIF_P, BIF_ARG_1, res);
+    } else {
+        /*
+         * Decrement ref count (and possibly delete the hash table
+         * and associated literal area).
+         */
+        dec_table_refc(BIF_P, trap_data->table);
+        trap_data->table = NULL; /* Prevent refc decrement */
+        BUMP_REDS(BIF_P, bump_reds);
+        BIF_RET(res);
+    }
+}
+
+static Eterm
+do_get_all(Process* c_p, TrapData* trap_data, Eterm res)
+{
+    HashTable* hash_table;
+    Uint remaining;
+    Uint idx;
+    Uint max_iter;
+    Uint i;
+    Eterm* hp;
+    Uint heap_size;
+    struct copy_term {
+        Uint key_size;
+        Eterm* tuple_ptr;
+    } *copy_data;
+
+    hash_table = trap_data->table;
+    idx = trap_data->idx;
+#if defined(DEBUG) || defined(VALGRIND)
+    max_iter = 50;
+#else
+    max_iter = ERTS_BIF_REDS_LEFT(c_p);
+#endif
+    remaining = trap_data->remaining < max_iter ?
+        trap_data->remaining : max_iter;
+    trap_data->remaining -= remaining;
+
+    copy_data = (struct copy_term *) erts_alloc(ERTS_ALC_T_TMP,
+                                                remaining *
+                                                sizeof(struct copy_term));
+    i = 0;
+    heap_size = (2 + 3) * remaining;
+    while (remaining != 0) {
+        Eterm term = hash_table->term[idx];
+        if (is_tuple(term)) {
+            Uint key_size;
+            Eterm* tup_val;
+
+            ASSERT(is_tuple_arity(term, 2));
+            tup_val = tuple_val(term);
+            key_size = size_object(tup_val[1]);
+            copy_data[i].key_size = key_size;
+            copy_data[i].tuple_ptr = tup_val;
+            heap_size += key_size;
+            i++;
+            remaining--;
+        }
+        idx++;
+    }
+    trap_data->idx = idx;
+
+    hp = HAlloc(c_p, heap_size);
+    remaining = i;
+    for (i = 0; i < remaining; i++) {
+        Eterm* tuple_ptr;
+        Uint key_size;
+        Eterm key;
+        Eterm tup;
+
+        tuple_ptr = copy_data[i].tuple_ptr;
+        key_size = copy_data[i].key_size;
+        key = copy_struct(tuple_ptr[1], key_size, &hp, &c_p->off_heap);
+        tup = TUPLE2(hp, key, tuple_ptr[2]);
+        hp += 3;
+        res = CONS(hp, tup, res);
+        hp += 2;
+    }
+    erts_free(ERTS_ALC_T_TMP, copy_data);
+    return res;
+}
+
+static BIF_RETTYPE
+persistent_term_info_trap(BIF_ALIST_1)
+{
+    TrapData* trap_data = (TrapData *) BIF_ARG_1;
+    Eterm res;
+    Uint bump_reds;
+    Binary* mbp;
+
+    mbp = erts_magic_ref2bin(BIF_ARG_1);
+    trap_data = ERTS_MAGIC_BIN_DATA(mbp);
+    bump_reds = trap_data->remaining;
+    res = do_info(BIF_P, trap_data);
+    if (trap_data->remaining > 0) {
+        ASSERT(res == am_ok);
+        BUMP_ALL_REDS(BIF_P);
+        BIF_TRAP1(&persistent_term_info_export, BIF_P, BIF_ARG_1);
+    } else {
+        /*
+         * Decrement ref count (and possibly delete the hash table
+         * and associated literal area).
+         */
+        dec_table_refc(BIF_P, trap_data->table);
+        trap_data->table = NULL; /* Prevent refc decrement */
+        BUMP_REDS(BIF_P, bump_reds);
+        ASSERT(is_map(res));
+        BIF_RET(res);
+    }
+}
+
+#define DECL_AM(S) Eterm AM_ ## S = am_atom_put(#S, sizeof(#S) - 1)
+
+static Eterm
+do_info(Process* c_p, TrapData* trap_data)
+{
+    HashTable* hash_table;
+    Uint remaining;
+    Uint idx;
+    Uint max_iter;
+
+    hash_table = trap_data->table;
+    idx = trap_data->idx;
+#if defined(DEBUG) || defined(VALGRIND)
+    max_iter = 50;
+#else
+    max_iter = ERTS_BIF_REDS_LEFT(c_p);
+#endif
+    remaining = trap_data->remaining < max_iter ? trap_data->remaining : max_iter;
+    trap_data->remaining -= remaining;
+    while (remaining != 0) {
+        if (is_boxed(hash_table->term[idx])) {
+            ErtsLiteralArea* area;
+            area = term_to_area(hash_table->term[idx]);
+            trap_data->memory += sizeof(ErtsLiteralArea) +
+                sizeof(Eterm) * (area->end - area->start - 1);
+            remaining--;
+        }
+        idx++;
+    }
+    trap_data->idx = idx;
+    if (trap_data->remaining > 0) {
+        return am_ok;           /* Dummy return value */
+    } else {
+        Eterm* hp;
+        Eterm count_term;
+        Eterm memory_term;
+        Eterm res;
+        Uint memory;
+        Uint hsz = MAP_SZ(2);
+
+        memory = sizeof(HashTable) + (trap_data->table->allocated-1) *
+            sizeof(Eterm) + trap_data->memory;
+        (void) erts_bld_uint(NULL, &hsz, hash_table->num_entries);
+        (void) erts_bld_uint(NULL, &hsz, memory);
+        hp = HAlloc(c_p, hsz);
+	count_term = erts_bld_uint(&hp, NULL, hash_table->num_entries);
+	memory_term = erts_bld_uint(&hp, NULL, memory);
+        res = MAP2(hp, am_count, count_term, am_memory, memory_term);
+        return res;
+    }
+}
+
+#undef DECL_AM
+
+static Eterm
+alloc_trap_data(Process* c_p)
+{
+    Binary* mbp = erts_create_magic_binary(sizeof(TrapData),
+                                           cleanup_trap_data);
+    Eterm* hp;
+
+    hp = HAlloc(c_p, ERTS_MAGIC_REF_THING_SIZE);
+    return erts_mk_magic_ref(&hp, &MSO(c_p), mbp);
+}
+
+static int
+cleanup_trap_data(Binary *bp)
+{
+    TrapData* trap_data = ERTS_MAGIC_BIN_DATA(bp);
+
+    if (trap_data->table) {
+        /*
+         * The process has been killed and is now exiting.
+         * Decrement the reference counter for the table.
+         */
+        dec_table_refc(NULL, trap_data->table);
+    }
+    return 1;
+}
+
+static Uint
+lookup(HashTable* hash_table, Eterm key)
+{
+    Uint mask = hash_table->mask;
+    Eterm* table = hash_table->term;
+    Uint32 idx = make_internal_hash(key, 0);
+    Eterm term;
+
+    do {
+        idx++;
+        term = table[idx & mask];
+    } while (is_boxed(term) && !EQ(key, (tuple_val(term))[1]));
+    return idx & mask;
+}
+
+static HashTable*
+tmp_table_copy(HashTable* old_table)
+{
+    Uint size = old_table->allocated;
+    HashTable* tmp_table;
+    Uint i;
+
+    tmp_table = (HashTable *) erts_alloc(ERTS_ALC_T_TMP,
+                                         sizeof(HashTable) +
+                                         sizeof(Eterm) * (size-1));
+    *tmp_table = *old_table;
+    for (i = 0; i < size; i++) {
+        tmp_table->term[i] = old_table->term[i];
+    }
+    return tmp_table;
+}
+
+static HashTable*
+copy_table(HashTable* old_table, Uint new_size, int rehash)
+{
+    HashTable* new_table;
+    Uint old_size = old_table->allocated;
+    Uint i;
+
+    new_table = (HashTable *) erts_alloc(ERTS_ALC_T_PERSISTENT_TERM,
+                                         sizeof(HashTable) +
+                                         sizeof(Eterm) * (new_size-1));
+    if (old_table->allocated == new_size && !rehash) {
+        /*
+         * Same size and no key deleted. Make an exact copy of the table.
+         */
+        *new_table = *old_table;
+        for (i = 0; i < new_size; i++) {
+            new_table->term[i] = old_table->term[i];
+        }
+    } else {
+        /*
+         * The size of the table has changed or an element has been
+         * deleted. Must rehash, by inserting all old terms into the
+         * new (empty) table.
+         */
+        new_table->allocated = new_size;
+        new_table->num_entries = old_table->num_entries;
+        new_table->mask = new_size - 1;
+        for (i = 0; i < new_size; i++) {
+            new_table->term[i] = NIL;
+        }
+        for (i = 0; i < old_size; i++) {
+            if (is_tuple(old_table->term[i])) {
+                Eterm key = tuple_val(old_table->term[i])[1];
+                Uint entry_index = lookup(new_table, key);
+                ASSERT(is_nil(new_table->term[entry_index]));
+                new_table->term[entry_index] = old_table->term[i];
+            }
+        }
+    }
+    new_table->first_to_delete = 0;
+    new_table->num_to_delete = 0;
+    erts_atomic_init_nob(&new_table->refc, (erts_aint_t)1);
+    return new_table;
+}
+
+static void
+mark_for_deletion(HashTable* hash_table, Uint entry_index)
+{
+    hash_table->first_to_delete = entry_index;
+    hash_table->num_to_delete = 1;
+}
+
+static ErtsLiteralArea*
+term_to_area(Eterm tuple)
+{
+    ASSERT(is_tuple_arity(tuple, 2));
+    return (ErtsLiteralArea *) (((char *) tuple_val(tuple)) -
+                                offsetof(ErtsLiteralArea, start));
+}
+
+static void
+table_updater(void* data)
+{
+    HashTable* old_table;
+    HashTable* new_table;
+
+    old_table = (HashTable *) erts_atomic_read_nob(&the_hash_table);
+    new_table = (HashTable *) data;
+    ASSERT(new_table->num_to_delete == 0);
+    erts_atomic_set_nob(&the_hash_table, (erts_aint_t)new_table);
+    append_to_delete_queue(old_table);
+    erts_schedule_thr_prgr_later_op(table_deleter,
+                                    old_table,
+                                    &old_table->thr_prog_op);
+    release_update_permission(1);
+}
+
+static void
+table_deleter(void* data)
+{
+    HashTable* old_table = (HashTable *) data;
+
+    dec_table_refc(NULL, old_table);
+}
+
+static void
+dec_table_refc(Process* c_p, HashTable* old_table)
+{
+    erts_aint_t refc = erts_atomic_dec_read_nob(&old_table->refc);
+
+    if (refc == 0) {
+        HashTable* to_delete;
+
+        while ((to_delete = next_to_delete()) != NULL) {
+            delete_table(c_p, to_delete);
+        }
+    }
+}
+
+static void
+delete_table(Process* c_p, HashTable* table)
+{
+    Uint idx = table->first_to_delete;
+    Uint n = table->num_to_delete;
+
+    /*
+     * There are no longer any references to this hash table.
+     *
+     * Any literals pointed for deletion can be queued for
+     * deletion and the table itself can be deallocated.
+     */
+
+#ifdef DEBUG
+    if (n == 1) {
+        ASSERT(is_tuple_arity(table->term[idx], 2));
+    }
+#endif
+
+    while (n > 0) {
+        Eterm term = table->term[idx];
+
+        if (is_tuple_arity(term, 2)) {
+            if (is_immed(tuple_val(term)[2])) {
+                erts_release_literal_area(term_to_area(term));
+            } else {
+                erts_queue_release_literals(c_p, term_to_area(term));
+            }
+        }
+        idx++, n--;
+    }
+    erts_free(ERTS_ALC_T_PERSISTENT_TERM, table);
+}
+
+/*
+ * Caller *must* yield if this function returns 0.
+ */
+
+static int
+try_seize_update_permission(Process* c_p)
+{
+    int success;
+
+    ASSERT(!erts_thr_progress_is_blocking()); /* to avoid deadlock */
+    ASSERT(c_p != NULL);
+
+    erts_mtx_lock(&update_table_permission_mtx);
+    ASSERT(updater_process != c_p);
+    success = (updater_process == NULL);
+    if (success) {
+        updater_process = c_p;
+    } else {
+        struct update_queue_item* qitem;
+        qitem = erts_alloc(ERTS_ALC_T_PERSISTENT_LOCK_Q, sizeof(*qitem));
+        qitem->p = c_p;
+        erts_proc_inc_refc(c_p);
+        qitem->next = update_queue;
+        update_queue = qitem;
+        erts_suspend(c_p, ERTS_PROC_LOCK_MAIN, NULL);
+    }
+    erts_mtx_unlock(&update_table_permission_mtx);
+    return success;
+}
+
+static void
+release_update_permission(int release_updater)
+{
+    erts_mtx_lock(&update_table_permission_mtx);
+    ASSERT(updater_process != NULL);
+
+    if (release_updater) {
+        erts_proc_lock(updater_process, ERTS_PROC_LOCK_STATUS);
+        if (!ERTS_PROC_IS_EXITING(updater_process)) {
+            erts_resume(updater_process, ERTS_PROC_LOCK_STATUS);
+        }
+        erts_proc_unlock(updater_process, ERTS_PROC_LOCK_STATUS);
+    }
+    updater_process = NULL;
+
+    while (update_queue != NULL) { /* Unleash the entire herd */
+	struct update_queue_item* qitem = update_queue;
+	erts_proc_lock(qitem->p, ERTS_PROC_LOCK_STATUS);
+	if (!ERTS_PROC_IS_EXITING(qitem->p)) {
+	    erts_resume(qitem->p, ERTS_PROC_LOCK_STATUS);
+	}
+	erts_proc_unlock(qitem->p, ERTS_PROC_LOCK_STATUS);
+	update_queue = qitem->next;
+	erts_proc_dec_refc(qitem->p);
+	erts_free(ERTS_ALC_T_PERSISTENT_LOCK_Q, qitem);
+    }
+    erts_mtx_unlock(&update_table_permission_mtx);
+}
+
+static void
+suspend_updater(Process* c_p)
+{
+#ifdef DEBUG
+    ASSERT(c_p != NULL);
+    erts_mtx_lock(&update_table_permission_mtx);
+    ASSERT(updater_process == c_p);
+    erts_mtx_unlock(&update_table_permission_mtx);
+#endif
+    erts_suspend(c_p, ERTS_PROC_LOCK_MAIN, NULL);
+}
+
+static void
+append_to_delete_queue(HashTable* table)
+{
+    erts_mtx_lock(&delete_queue_mtx);
+    table->delete_next = NULL;
+    *delete_queue_tail = table;
+    delete_queue_tail = &table->delete_next;
+    erts_mtx_unlock(&delete_queue_mtx);
+}
+
+static HashTable*
+next_to_delete(void)
+{
+    HashTable* table;
+
+    erts_mtx_lock(&delete_queue_mtx);
+    table = delete_queue_head;
+    if (table) {
+        if (erts_atomic_read_nob(&table->refc)) {
+            /*
+             * This hash table is still referenced. Hash tables
+             * must be deleted in order, so we return a NULL
+             * pointer.
+             */
+            table = NULL;
+        } else {
+            /*
+             * Remove the first hash table from the queue.
+             */
+            delete_queue_head = table->delete_next;
+            if (delete_queue_head == NULL) {
+                delete_queue_tail = &delete_queue_head;
+            }
+        }
+    }
+    erts_mtx_unlock(&delete_queue_mtx);
+    return table;
+}
diff --git a/erts/emulator/beam/erl_init.c b/erts/emulator/beam/erl_init.c
index 57c6c10c7f..f687dcf335 100644
--- a/erts/emulator/beam/erl_init.c
+++ b/erts/emulator/beam/erl_init.c
@@ -354,6 +354,7 @@ erl_init(int ncpu,
     erts_init_bif();
     erts_init_bif_chksum();
     erts_init_bif_binary();
+    erts_init_bif_persistent_term();
     erts_init_bif_re();
     erts_init_unicode(); /* after RE to get access to PCRE unicode */
     erts_init_external();
diff --git a/erts/emulator/beam/erl_lock_check.c b/erts/emulator/beam/erl_lock_check.c
index 463ae898a3..1416c5f96c 100644
--- a/erts/emulator/beam/erl_lock_check.c
+++ b/erts/emulator/beam/erl_lock_check.c
@@ -97,6 +97,8 @@ static erts_lc_lock_order_t erts_lock_order[] = {
     {	"proc_btm",				"pid"			},
     {	"dist_entry",				"address"		},
     {	"dist_entry_links",			"address"		},
+    {   "update_persistent_term_permission",    NULL                    },
+    {   "persistent_term_delete_permission",    NULL                    },
     {   "code_write_permission",                NULL                    },
     {	"purge_state",		      		NULL			},
     {	"proc_status",				"pid"			},
diff --git a/erts/emulator/beam/erl_process_dump.c b/erts/emulator/beam/erl_process_dump.c
index 243db4c734..ac5054ea10 100644
--- a/erts/emulator/beam/erl_process_dump.c
+++ b/erts/emulator/beam/erl_process_dump.c
@@ -58,6 +58,7 @@ static void dump_externally(fmtfn_t to, void *to_arg, Eterm term);
 static void mark_literal(Eterm* ptr);
 static void init_literal_areas(void);
 static void dump_literals(fmtfn_t to, void *to_arg);
+static void dump_persistent_terms(fmtfn_t to, void *to_arg);
 static void dump_module_literals(fmtfn_t to, void *to_arg,
                                  ErtsLiteralArea* lit_area);
 
@@ -74,6 +75,7 @@ erts_deep_process_dump(fmtfn_t to, void *to_arg)
 
     all_binaries = NULL;
     init_literal_areas();
+    erts_init_persistent_dumping();
 
     for (i = 0; i < max; i++) {
 	Process *p = erts_pix2proc(i);
@@ -93,6 +95,7 @@ erts_deep_process_dump(fmtfn_t to, void *to_arg)
        }
     }
 
+    dump_persistent_terms(to, to_arg);
     dump_literals(to, to_arg);
     dump_binaries(to, to_arg, all_binaries);
 }
@@ -775,6 +778,9 @@ init_literal_areas(void)
     qsort(lit_areas, num_lit_areas, sizeof(ErtsLiteralArea *),
           compare_areas);
 
+    qsort(erts_persistent_areas, erts_num_persistent_areas,
+          sizeof(ErtsLiteralArea *), compare_areas);
+
     erts_runlock_old_code(code_ix);
 }
 
@@ -796,6 +802,13 @@ static void mark_literal(Eterm* ptr)
 
     ap = bsearch(ptr, lit_areas, num_lit_areas, sizeof(ErtsLiteralArea*),
                  search_areas);
+    if (ap == 0) {
+        ap = bsearch(ptr, erts_persistent_areas,
+                     erts_num_persistent_areas,
+                     sizeof(ErtsLiteralArea*),
+                     search_areas);
+    }
+
 
     /*
      * If the literal was created by native code, this search will not
@@ -807,12 +820,12 @@ static void mark_literal(Eterm* ptr)
     }
 }
 
-
 static void
 dump_literals(fmtfn_t to, void *to_arg)
 {
     ErtsCodeIndex code_ix;
     int i;
+    Uint idx;
 
     code_ix = erts_active_code_ix();
     erts_rlock_old_code(code_ix);
@@ -825,6 +838,28 @@ dump_literals(fmtfn_t to, void *to_arg)
     }
 
     erts_runlock_old_code(code_ix);
+
+    for (idx = 0; idx < erts_num_persistent_areas; idx++) {
+        dump_module_literals(to, to_arg, erts_persistent_areas[idx]);
+    }
+}
+
+static void
+dump_persistent_terms(fmtfn_t to, void *to_arg)
+{
+    Uint idx;
+
+    erts_print(to, to_arg, "=persistent_terms\n");
+
+    for (idx = 0; idx < erts_num_persistent_areas; idx++) {
+        ErtsLiteralArea* ap = erts_persistent_areas[idx];
+        Eterm tuple = make_tuple(ap->start);
+        Eterm* tup_val = tuple_val(tuple);
+
+	dump_element(to, to_arg, tup_val[1]);
+        erts_putc(to, to_arg, '|');
+	dump_element_nl(to, to_arg, tup_val[2]);
+    }
 }
 
 static void
@@ -963,7 +998,8 @@ dump_module_literals(fmtfn_t to, void *to_arg, ErtsLiteralArea* lit_area)
                     }
                     erts_putc(to, to_arg, '\n');
                 }
-            } else if (is_export_header(w)) {
+            } else {
+                /* Dump everything else in the external format */
                 dump_externally(to, to_arg, term);
                 erts_putc(to, to_arg, '\n');
             }
diff --git a/erts/emulator/beam/global.h b/erts/emulator/beam/global.h
index 54d309ff2f..0631404599 100644
--- a/erts/emulator/beam/global.h
+++ b/erts/emulator/beam/global.h
@@ -1242,6 +1242,13 @@ Sint erts_re_set_loop_limit(Sint limit);
 void erts_init_bif_binary(void);
 Sint erts_binary_set_loop_limit(Sint limit);
 
+/* erl_bif_persistent.c */
+void erts_init_bif_persistent_term(void);
+Uint erts_persistent_term_count(void);
+void erts_init_persistent_dumping(void);
+extern ErtsLiteralArea** erts_persistent_areas;
+extern Uint erts_num_persistent_areas;
+
 /* external.c */
 void erts_init_external(void);
 
diff --git a/erts/emulator/test/Makefile b/erts/emulator/test/Makefile
index bf00de2204..d201ea6ee1 100644
--- a/erts/emulator/test/Makefile
+++ b/erts/emulator/test/Makefile
@@ -92,6 +92,7 @@ MODULES= \
 	port_SUITE \
 	port_bif_SUITE \
 	prim_eval_SUITE \
+	persistent_term_SUITE \
 	process_SUITE \
 	pseudoknot_SUITE \
 	receive_SUITE \
diff --git a/erts/emulator/test/persistent_term_SUITE.erl b/erts/emulator/test/persistent_term_SUITE.erl
new file mode 100644
index 0000000000..58cd3276b0
--- /dev/null
+++ b/erts/emulator/test/persistent_term_SUITE.erl
@@ -0,0 +1,614 @@
+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 2017. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%5
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%
+%% %CopyrightEnd%
+%%
+
+-module(persistent_term_SUITE).
+-include_lib("common_test/include/ct.hrl").
+
+-export([all/0,suite/0,
+	 basic/1,purging/1,sharing/1,get_trapping/1,
+         info/1,info_trapping/1,killed_while_trapping/1,
+         off_heap_values/1,keys/1,collisions/1,
+         init_restart/1]).
+
+%%
+-export([test_init_restart_cmd/1]).
+
+suite() ->
+    [{ct_hooks,[ts_install_cth]},
+     {timetrap,{minutes,10}}].
+
+all() ->
+    [basic,purging,sharing,get_trapping,info,info_trapping,
+     killed_while_trapping,off_heap_values,keys,collisions,
+     init_restart].
+
+basic(_Config) ->
+    Chk = chk(),
+    N = 777,
+    Seq = lists:seq(1, N),
+    par(2, N, Seq),
+    seq(3, Seq),
+    seq(3, Seq),                                %Same values.
+    _ = [begin
+             Key = {?MODULE,{key,I}},
+             true = persistent_term:erase(Key),
+             false = persistent_term:erase(Key),
+             {'EXIT',{badarg,_}} = (catch persistent_term:get(Key))
+         end || I <- Seq],
+    [] = [P || {{?MODULE,_},_}=P <- persistent_term:get()],
+    chk(Chk).
+
+par(C, N, Seq) ->
+    _ = [spawn_link(fun() ->
+                            ok = persistent_term:put({?MODULE,{key,I}},
+                                                     {value,C*I})
+                    end) || I <- Seq],
+    Result = wait(N),
+    _ = [begin
+             Double = C*I,
+             {{?MODULE,{key,I}},{value,Double}} = Res
+         end || {I,Res} <- lists:zip(Seq, Result)],
+    ok.
+
+seq(C, Seq) ->
+    _ = [ok = persistent_term:put({?MODULE,{key,I}}, {value,C*I}) ||
+            I <- Seq],
+    All = persistent_term:get(),
+    All = [P || {{?MODULE,_},_}=P <- persistent_term:get()],
+    All = [{Key,persistent_term:get(Key)} || {Key,_} <- All],
+    Result = lists:sort(All),
+    _ = [begin
+             Double = C*I,
+             {{?MODULE,{key,I}},{value,Double}} = Res
+         end || {I,Res} <- lists:zip(Seq, Result)],
+    ok.
+
+wait(N) ->
+    All = [P || {{?MODULE,_},_}=P <- persistent_term:get()],
+    case length(All) of
+        N ->
+            All = [{Key,persistent_term:get(Key)} || {Key,_} <- All],
+            lists:sort(All);
+        _ ->
+            receive after 10 -> ok end,
+            wait(N)
+    end.
+
+%% Make sure that terms that have been erased are copied into all
+%% processes that still hold a pointer to them.
+
+purging(_Config) ->
+    Chk = chk(),
+    do_purging(fun(K) -> persistent_term:put(K, {?MODULE,new}) end,
+               replaced),
+    do_purging(fun persistent_term:erase/1, erased),
+    chk(Chk).
+
+do_purging(Eraser, Type) ->
+    Parent = self(),
+    Key = {?MODULE,?FUNCTION_NAME},
+    ok = persistent_term:put(Key, {term,[<<"abc",0:777/unit:8>>]}),
+    Ps0 = [spawn_monitor(fun() -> purging_tester(Parent, Key) end) ||
+              _ <- lists:seq(1, 50)],
+    Ps = maps:from_list(Ps0),
+    purging_recv(gotten, Ps),
+    Eraser(Key),
+    _ = [P ! {Parent,Type} || P <- maps:keys(Ps)],
+    purging_wait(Ps).
+
+purging_recv(Tag, Ps) when map_size(Ps) > 0 ->
+    receive
+        {Pid,Tag} ->
+            true = is_map_key(Pid, Ps),
+            purging_recv(Tag, maps:remove(Pid, Ps))
+    end;
+purging_recv(_, _) -> ok.
+
+purging_wait(Ps) when map_size(Ps) > 0 ->
+    receive
+        {'DOWN',Ref,process,Pid,Reason} ->
+            normal = Reason,
+            Ref = map_get(Pid, Ps),
+            purging_wait(maps:remove(Pid, Ps))
+    end;
+purging_wait(_) -> ok.
+
+purging_tester(Parent, Key) ->
+    Term = persistent_term:get(Key),
+    purging_check_term(Term),
+    0 = erts_debug:size_shared(Term),
+    Parent ! {self(),gotten},
+    receive
+        {Parent,erased} ->
+            {'EXIT',{badarg,_}} = (catch persistent_term:get(Key)),
+            purging_tester_1(Term);
+        {Parent,replaced} ->
+            {?MODULE,new} = persistent_term:get(Key),
+            purging_tester_1(Term)
+    end.
+
+%% Wait for the term to be copied into this process.
+purging_tester_1(Term) ->
+    purging_check_term(Term),
+    receive after 1 -> ok end,
+    case erts_debug:size_shared(Term) of
+        0 ->
+            purging_tester_1(Term);
+        Size ->
+            %% The term has been copied into this process.
+            purging_check_term(Term),
+            Size = erts_debug:size(Term)
+    end.
+
+purging_check_term({term,[<<"abc",0:777/unit:8>>]}) ->
+    ok.
+
+%% Test that sharing is preserved when storing terms.
+
+sharing(_Config) ->
+    Chk = chk(),
+    Depth = 10,
+    Size = 2*Depth,
+    Shared = lists:foldl(fun(_, A) -> [A|A] end,
+                         [], lists:seq(1, Depth)),
+    Size = erts_debug:size(Shared),
+    Key = {?MODULE,?FUNCTION_NAME},
+    ok = persistent_term:put(Key, Shared),
+    SharedStored = persistent_term:get(Key),
+    Size = erts_debug:size(SharedStored),
+    0 = erts_debug:size_shared(SharedStored),
+
+    {Pid,Ref} = spawn_monitor(fun() ->
+                                      Term = persistent_term:get(Key),
+                                      Size = erts_debug:size(Term),
+                                      0 = erts_debug:size_shared(Term),
+                                      true = Term =:= SharedStored
+                              end),
+    receive
+        {'DOWN',Ref,process,Pid,normal} ->
+            true = persistent_term:erase(Key),
+            Size = erts_debug:size(SharedStored),
+            chk(Chk)
+    end.
+
+%% Test trapping of persistent_term:get/0.
+
+get_trapping(_Config) ->
+    Chk = chk(),
+
+    %% Assume that the get/0 traps after 4000 iterations
+    %% in a non-debug emulator.
+    N = case test_server:timetrap_scale_factor() of
+            1 -> 10000;
+            _ -> 1000
+        end,
+    spawn_link(fun() -> get_trapping_create(N) end),
+    All = do_get_trapping(N, []),
+    N = get_trapping_check_result(lists:sort(All), 1),
+    erlang:garbage_collect(),
+    get_trapping_erase(N),
+    chk(Chk).
+
+do_get_trapping(N, Prev) ->
+    case persistent_term:get() of
+        Prev when length(Prev) >= N ->
+            All = [P || {{?MODULE,{get_trapping,_}},_}=P <- Prev],
+            case length(All) of
+                N -> All;
+                _ -> do_get_trapping(N, Prev)
+            end;
+        New ->
+            receive after 1 -> ok end,
+            do_get_trapping(N, New)
+    end.
+
+get_trapping_create(0) ->
+    ok;
+get_trapping_create(N) ->
+    ok = persistent_term:put({?MODULE,{get_trapping,N}}, N),
+    get_trapping_create(N-1).
+
+get_trapping_check_result([{{?MODULE,{get_trapping,N}},N}|T], N) ->
+    get_trapping_check_result(T, N+1);
+get_trapping_check_result([], N) -> N-1.
+
+get_trapping_erase(0) ->
+    ok;
+get_trapping_erase(N) ->
+    true = persistent_term:erase({?MODULE,{get_trapping,N}}),
+    get_trapping_erase(N-1).
+
+%% Test retrieving information about persistent terms.
+
+info(_Config) ->
+    Chk = chk(),
+
+    %% White box test of info/0.
+    N = 100,
+    try
+        Overhead = info_literal_area_overhead(),
+        io:format("Overhead = ~p\n", [Overhead]),
+        info_wb(N, Overhead, info_info())
+    after
+        _ = [_ = persistent_term:erase({?MODULE,I}) ||
+                I <- lists:seq(1, N)]
+    end,
+
+    chk(Chk).
+
+%% White box test of persistent_term:info/0. We take into account
+%% that there might already exist persistent terms (created by the
+%% OTP standard libraries), but we assume that they are not
+%% changed during the execution of this test case.
+
+info_wb(0, _, _) ->
+    ok;
+info_wb(N, Overhead, {BaseCount,BaseMemory}) ->
+    Key = {?MODULE,N},
+    Value = lists:seq(1, N),
+    ok = persistent_term:put(Key, Value),
+
+    %% Calculate the extra memory needed for this term.
+    WordSize = erlang:system_info(wordsize),
+    ExtraMemory = Overhead + 2 * N * WordSize,
+
+    %% Call persistent_term:info/0.
+    {Count,Memory} = info_info(),
+
+    %% There should be one more persistent term.
+    Count = BaseCount + 1,
+
+    %% Verify that the amount of memory is correct.
+    case BaseMemory + ExtraMemory of
+        Memory ->
+            %% Exactly right. The size of the hash table was not changed.
+            ok;
+        Expected ->
+            %% The size of the hash table has been doubled to avoid filling
+            %% the table to more than 50 percent. The previous number
+            %% of entries must have been exactly half the size of the
+            %% hash table. The expected number of extra words added by
+            %% the resizing will be twice that number.
+            ExtraWords = BaseCount * 2,
+            true = ExtraWords * WordSize =:= (Memory - Expected)
+    end,
+    info_wb(N-1, Overhead, {Count,Memory}).
+
+info_info() ->
+    #{count:=Count,memory:=Memory} = persistent_term:info(),
+    true = is_integer(Count) andalso Count >= 0,
+    true = is_integer(Memory) andalso Memory >= 0,
+    {Count,Memory}.
+
+%% Calculate the number of extra bytes needed for storing each term in
+%% the literal, assuming that the key is a tuple of size 2 with
+%% immediate elements. The calculated number is the size of the
+%% ErtsLiteralArea struct excluding the storage for the literal term
+%% itself.
+
+info_literal_area_overhead() ->
+    Key1 = {?MODULE,1},
+    Key2 = {?MODULE,2},
+    #{memory:=Mem0} = persistent_term:info(),
+    ok = persistent_term:put(Key1, literal),
+    #{memory:=Mem1} = persistent_term:info(),
+    ok = persistent_term:put(Key2, literal),
+    #{memory:=Mem2} = persistent_term:info(),
+    true = persistent_term:erase(Key1),
+    true = persistent_term:erase(Key2),
+
+    %% The size of the hash table may have doubled when inserting
+    %% one of the keys. To avoiding counting the change in the hash
+    %% table size, take the smaller size increase.
+    min(Mem2-Mem1, Mem1-Mem0).
+
+%% Test trapping of persistent_term:info/0.
+
+info_trapping(_Config) ->
+    Chk = chk(),
+
+    %% Assume that the info/0 traps after 4000 iterations
+    %% in a non-debug emulator.
+    N = case test_server:timetrap_scale_factor() of
+            1 -> 10000;
+            _ -> 1000
+        end,
+    spawn_link(fun() -> info_trapping_create(N) end),
+    All = do_info_trapping(N, 0),
+    N = info_trapping_check_result(lists:sort(All), 1),
+    erlang:garbage_collect(),
+    info_trapping_erase(N),
+    chk(Chk).
+
+do_info_trapping(N, PrevMem) ->
+    case info_info() of
+        {N,Mem} ->
+            true = Mem >= PrevMem,
+            All = [P || {{?MODULE,{info_trapping,_}},_}=P <- persistent_term:get()],
+            case length(All) of
+                N -> All;
+                _ -> do_info_trapping(N, PrevMem)
+            end;
+        {_,Mem} ->
+            true = Mem >= PrevMem,
+            receive after 1 -> ok end,
+            do_info_trapping(N, Mem)
+    end.
+
+info_trapping_create(0) ->
+    ok;
+info_trapping_create(N) ->
+    ok = persistent_term:put({?MODULE,{info_trapping,N}}, N),
+    info_trapping_create(N-1).
+
+info_trapping_check_result([{{?MODULE,{info_trapping,N}},N}|T], N) ->
+    info_trapping_check_result(T, N+1);
+info_trapping_check_result([], N) -> N-1.
+
+info_trapping_erase(0) ->
+    ok;
+info_trapping_erase(N) ->
+    true = persistent_term:erase({?MODULE,{info_trapping,N}}),
+    info_trapping_erase(N-1).
+
+%% Test that hash tables are deallocated if a process running
+%% persistent_term:get/0 is killed.
+
+killed_while_trapping(_Config) ->
+    Chk = chk(),
+    N = case test_server:timetrap_scale_factor() of
+            1 -> 20000;
+            _ -> 2000
+        end,
+    kwt_put(N),
+    kwt_spawn(10),
+    kwt_erase(N),
+    chk(Chk).
+
+kwt_put(0) ->
+    ok;
+kwt_put(N) ->
+    ok = persistent_term:put({?MODULE,{kwt,N}}, N),
+    kwt_put(N-1).
+
+kwt_spawn(0) ->
+    ok;
+kwt_spawn(N) ->
+    Pids = [spawn(fun kwt_getter/0) || _ <- lists:seq(1, 20)],
+    erlang:yield(),
+    _ = [exit(Pid, kill) || Pid <- Pids],
+    kwt_spawn(N-1).
+
+kwt_getter() ->
+    _ = persistent_term:get(),
+    kwt_getter().
+
+kwt_erase(0) ->
+    ok;
+kwt_erase(N) ->
+    true = persistent_term:erase({?MODULE,{kwt,N}}),
+    kwt_erase(N-1).
+
+%% Test storing off heap values (such as ref-counted binaries).
+
+off_heap_values(_Config) ->
+    Chk = chk(),
+    Key = {?MODULE,?FUNCTION_NAME},
+    Val = {a,list_to_binary(lists:seq(0, 255)),make_ref(),fun() -> ok end},
+    ok = persistent_term:put(Key, Val),
+    FetchedVal = persistent_term:get(Key),
+    Val = FetchedVal,
+    true = persistent_term:erase(Key),
+    off_heap_values_wait(FetchedVal, Val),
+    chk(Chk).
+
+off_heap_values_wait(FetchedVal, Val) ->
+    case erts_debug:size_shared(FetchedVal) of
+        0 ->
+            Val = FetchedVal,
+            ok;
+        _ ->
+            erlang:yield(),
+            off_heap_values_wait(FetchedVal, Val)
+    end.
+
+%% Test some more data types as keys. Use the module name as a key
+%% to minimize the risk of collision with any key used
+%% by the OTP libraries.
+
+keys(_Config) ->
+    Chk = chk(),
+    do_key(?MODULE),
+    do_key([?MODULE]),
+    do_key(?MODULE_STRING),
+    do_key(list_to_binary(?MODULE_STRING)),
+    chk(Chk).
+
+do_key(Key) ->
+    Val = term_to_binary(Key),
+    ok = persistent_term:put(Key, Val),
+    StoredVal = persistent_term:get(Key),
+    Val = StoredVal,
+    true = persistent_term:erase(Key).
+
+%% Create persistent terms with keys that are known to collide.
+%% Delete them in random order, making sure that all others
+%% terms can still be found.
+
+collisions(_Config) ->
+    Chk = chk(),
+
+    %% Create persistent terms with random keys.
+    Keys = lists:flatten(colliding_keys()),
+    Kvs = [{K,rand:uniform(1000)} || K <- Keys],
+    _ = [ok = persistent_term:put(K, V) || {K,V} <- Kvs],
+    _ = [V = persistent_term:get(K) || {K,V} <- Kvs],
+
+    %% Now delete the persistent terms in random order.
+    collisions_delete(lists:keysort(2, Kvs)),
+
+    chk(Chk).
+
+collisions_delete([{Key,Val}|Kvs]) ->
+    Val = persistent_term:get(Key),
+    true = persistent_term:erase(Key),
+    true = lists:sort(persistent_term:get()) =:= lists:sort(Kvs),
+    _ = [V = persistent_term:get(K) || {K,V} <- Kvs],
+    collisions_delete(Kvs);
+collisions_delete([]) ->
+    ok.
+
+colliding_keys() ->
+    %% Collisions found by Jesper L. Andersen for breaking maps.
+    L = [[764492191,2361333849],
+         [49527266765044,90940896816021,20062927283041,267080852079651],
+         [249858369443708,206247021789428,20287304470696,25847120931175],
+         [10645228898670,224705626119556,267405565521452,258214397180678],
+         [264783762221048,166955943492306,98802957003141,102012488332476],
+         [69425677456944,177142907243411,137138950917722,228865047699598],
+         [116031213307147,29203342183358,37406949328742,255198080174323],
+         [200358182338308,235207156008390,120922906095920,116215987197289],
+         [58728890318426,68877471005069,176496507286088,221041411345780],
+         [91094120814795,50665258299931,256093108116737,19777509566621],
+         [74646746200247,98350487270564,154448261001199,39881047281135],
+         [23408943649483,164410325820923,248161749770122,274558342231648],
+         [169531547115055,213630535746863,235098262267796,200508473898303],
+         [235098564415817,85039146398174,51721575960328,173069189684390],
+         [176136386396069,155368359051606,147817099696487,265419485459634],
+         [137542881551462,40028925519736,70525669519846,63445773516557],
+         [173854695142814,114282444507812,149945832627054,99605565798831],
+         [177686773562184,127158716984798,132495543008547],
+         [227073396444896,139667311071766,158915951283562],
+         [26212438434289,94902985796531,198145776057315],
+         [266279278943923,58550737262493,74297973216378],
+         [32373606512065,131854353044428,184642643042326],
+         [34335377662439,85341895822066,273492717750246]],
+
+    %% Verify that the keys still collide (this will fail if the
+    %% internal hash function has been changed).
+    erts_debug:set_internal_state(available_internal_state, true),
+    try
+        case erlang:system_info(wordsize) of
+            8 ->
+                verify_colliding_keys(L);
+            4 ->
+                %% Not guaranteed to collide on a 32-bit system.
+                ok
+        end
+    after
+        erts_debug:set_internal_state(available_internal_state, false)
+    end,
+
+    L.
+
+verify_colliding_keys([[K|Ks]|Gs]) ->
+    Hash = internal_hash(K),
+    [Hash] = lists:usort([internal_hash(Key) || Key <- Ks]),
+    verify_colliding_keys(Gs);
+verify_colliding_keys([]) ->
+    ok.
+
+internal_hash(Term) ->
+    erts_debug:get_internal_state({internal_hash,Term}).
+
+%% Test that all persistent terms are erased by init:restart/0.
+
+init_restart(_Config) ->
+    File = "command_file",
+    ok = file:write_file(File, term_to_binary(restart)),
+    {ok,[[Erl]]} = init:get_argument(progname),
+    ModPath = filename:dirname(code:which(?MODULE)),
+    Cmd = Erl ++ " -pa " ++ ModPath ++ " -noshell "
+        "-run " ++ ?MODULE_STRING ++ " test_init_restart_cmd " ++
+        File,
+    io:format("~s\n", [Cmd]),
+    Expected = "12ok",
+    case os:cmd(Cmd) of
+        Expected ->
+            ok;
+        Actual ->
+            io:format("Expected: ~s", [Expected]),
+            io:format("Actual:   ~s\n", [Actual]),
+            ct:fail(unexpected_output)
+    end.
+
+test_init_restart_cmd([File]) ->
+    try
+        do_test_init_restart_cmd(File)
+    catch
+        C:R ->
+            io:format("\n~p ~p\n", [C,R]),
+            halt()
+    end,
+    receive
+        _ -> ok
+    end.
+
+do_test_init_restart_cmd(File) ->
+    {ok,Bin} = file:read_file(File),
+    Seq = lists:seq(1, 50),
+    case binary_to_term(Bin) of
+        restart ->
+            _ = [persistent_term:put({?MODULE,I}, {value,I}) ||
+                    I <- Seq],
+            ok = file:write_file(File, term_to_binary(was_restarted)),
+            io:put_chars("1"),
+            init:restart(),
+            receive
+                _ -> ok
+            end;
+        was_restarted ->
+            io:put_chars("2"),
+            ok = file:delete(File),
+            _ = [begin
+                     Key = {?MODULE,I},
+                     {'EXIT',{badarg,_}} = (catch persistent_term:get(Key))
+                 end || I <- Seq],
+            io:put_chars("ok"),
+            init:stop()
+    end.
+
+%% Check that there is the same number of persistents terms before
+%% and after each test case.
+
+chk() ->
+    persistent_term:info().
+
+chk(Chk) ->
+    Chk = persistent_term:info(),
+    Key = {?MODULE,?FUNCTION_NAME},
+    ok = persistent_term:put(Key, {term,Chk}),
+    Term = persistent_term:get(Key),
+    true = persistent_term:erase(Key),
+    chk_not_stuck(Term),
+    ok.
+
+chk_not_stuck(Term) ->
+    %% Hash tables to be deleted are put onto a queue.
+    %% Make sure that the queue isn't stuck by a table with
+    %% a non-zero ref count.
+
+    case erts_debug:size_shared(Term) of
+        0 ->
+            erlang:yield(),
+            chk_not_stuck(Term);
+        _ ->
+            ok
+    end.
diff --git a/erts/preloaded/ebin/erts_internal.beam b/erts/preloaded/ebin/erts_internal.beam
index 15c59de80a..f39c7aa8eb 100644
--- a/erts/preloaded/ebin/erts_internal.beam
+++ b/erts/preloaded/ebin/erts_internal.beam
diff --git a/erts/preloaded/ebin/init.beam b/erts/preloaded/ebin/init.beam
index 858a9dc63e..1e60ef7e88 100644
--- a/erts/preloaded/ebin/init.beam
+++ b/erts/preloaded/ebin/init.beam
diff --git a/erts/preloaded/ebin/persistent_term.beam b/erts/preloaded/ebin/persistent_term.beam
new file mode 100644
index 0000000000..79ef03b9a6
--- /dev/null
+++ b/erts/preloaded/ebin/persistent_term.beam
diff --git a/erts/preloaded/src/Makefile b/erts/preloaded/src/Makefile
index 4333f6643a..e768a8edbc 100644
--- a/erts/preloaded/src/Makefile
+++ b/erts/preloaded/src/Makefile
@@ -47,7 +47,8 @@ PRE_LOADED_ERL_MODULES = \
 	erts_internal \
 	erl_tracer \
 	erts_literal_area_collector \
-	erts_dirty_process_signal_handler
+	erts_dirty_process_signal_handler \
+        persistent_term
 
 PRE_LOADED_BEAM_MODULES = \
 	prim_eval
diff --git a/erts/preloaded/src/erts_internal.erl b/erts/preloaded/src/erts_internal.erl
index 88f47e917b..63b786a473 100644
--- a/erts/preloaded/src/erts_internal.erl
+++ b/erts/preloaded/src/erts_internal.erl
@@ -90,6 +90,8 @@
 
 -export([create_dist_channel/4]).
 
+-export([erase_persistent_terms/0]).
+
 %%
 %% Await result of send to port
 %%
@@ -691,3 +693,7 @@ process_flag(_Pid, _Flag, _Value) ->
                                  
 create_dist_channel(_Node, _DistCtrlr, _Flags, _Ver) ->
     erlang:nif_error(undefined).
+
+-spec erase_persistent_terms() -> 'ok'.
+erase_persistent_terms() ->
+    erlang:nif_error(undefined).
diff --git a/erts/preloaded/src/init.erl b/erts/preloaded/src/init.erl
index 253fcf7a1f..b4b8b3bf9b 100644
--- a/erts/preloaded/src/init.erl
+++ b/erts/preloaded/src/init.erl
@@ -552,6 +552,7 @@ stop(Reason,State) ->
 do_stop(restart,#state{start = Start, flags = Flags, args = Args}) ->
     %% Make sure we don't have any outstanding messages before doing the restart.
     flush(),
+    erts_internal:erase_persistent_terms(),
     boot(Start,Flags,Args);
 do_stop(reboot,_) ->
     halt();
diff --git a/erts/preloaded/src/persistent_term.erl b/erts/preloaded/src/persistent_term.erl
new file mode 100644
index 0000000000..5d0c266127
--- /dev/null
+++ b/erts/preloaded/src/persistent_term.erl
@@ -0,0 +1,55 @@
+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 2018. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%
+%% %CopyrightEnd%
+%%
+-module(persistent_term).
+
+-export([erase/1,get/0,get/1,info/0,put/2]).
+
+-type key() :: term().
+-type value() :: term().
+
+-spec erase(Key) -> Result when
+      Key :: key(),
+      Result :: boolean().
+erase(_Key) ->
+    erlang:nif_error(undef).
+
+-spec get() -> List when
+      List :: [{key(),value()}].
+get() ->
+    erlang:nif_error(undef).
+
+-spec get(Key) -> Value when
+      Key :: key(),
+      Value :: value().
+get(_Key) ->
+    erlang:nif_error(undef).
+
+-spec info() -> Info when
+      Info :: #{'count':=Count,'memory':=Memory},
+      Count :: non_neg_integer(),
+      Memory :: non_neg_integer().
+info() ->
+    erlang:nif_error(undef).
+
+-spec put(Key, Value) -> 'ok' when
+      Key :: key(),
+      Value :: value().
+put(_Key, _Value) ->
+    erlang:nif_error(undef).