From e146a3eec5a2d384260aa8829777c89eaab09cbd Mon Sep 17 00:00:00 2001
From: Lukas Larsson <lukas.larsson@erlang-solutions.com>
Date: Thu, 21 Apr 2016 18:36:45 +0200
Subject: erts: Implement max_heap_size process flag

The max_heap_size process flag can be used to limit the
growth of a process heap by killing it before it becomes
too large to handle. It is possible to set the maximum
using the `erl +hmax` option, `system_flag(max_heap_size, ...)`,
`spawn_opt(Fun, [{max_heap_size, ...}])` and
`process_flag(max_heap_size, ...)`.

It is possible to configure the behaviour of the process
when the maximum heap size is reached. The process may be
sent an untrappable exit signal with reason kill and/or
send an error_logger message with details on the process
state. A new trace event called gc_max_heap_size is
also triggered for the garbage_collection trace flag
when the heap grows larger than the configured size.

If kill and error_logger are disabled, it is still
possible to see that the maximum has been reached by
doing garbage collection tracing on the process.

The heap size is defined as the sum of the heap memory
that the process is currently using. This includes
all generational heaps, the stack, any messages that
are considered to be part of the heap and any extra
memory the garbage collector may need during collection.

In the current implementation this means that when a process
is set using on_heap message queue data mode, the messages
that are in the internal message queue are counted towards
this value. For off_heap, only matched messages count towards
the size of the heap. For mixed, it depends on race conditions
within the VM whether a message is part of the heap or not.

Below is an example run of the new behaviour:

Eshell V8.0  (abort with ^G)
1> f(P),P = spawn_opt(fun() -> receive ok -> ok end end, [{max_heap_size, 512}]).
<0.60.0>
2> erlang:trace(P, true, [garbage_collection, procs]).
1
3> [P ! lists:duplicate(M,M) || M <- lists:seq(1,15)],ok.
ok
4>
=ERROR REPORT==== 26-Apr-2016::16:25:10 ===
     Process:          <0.60.0>
     Context:          maximum heap size reached
     Max heap size:    512
     Total heap size:  723
     Kill:             true
     Error Logger:     true
     GC Info:          [{old_heap_block_size,0},
                        {heap_block_size,609},
                        {mbuf_size,145},
                        {recent_size,0},
                        {stack_size,9},
                        {old_heap_size,0},
                        {heap_size,211},
                        {bin_vheap_size,0},
                        {bin_vheap_block_size,46422},
                        {bin_old_vheap_size,0},
                        {bin_old_vheap_block_size,46422}]
flush().
Shell got {trace,<0.60.0>,gc_start,
                 [{old_heap_block_size,0},
                  {heap_block_size,233},
                  {mbuf_size,145},
                  {recent_size,0},
                  {stack_size,9},
                  {old_heap_size,0},
                  {heap_size,211},
                  {bin_vheap_size,0},
                  {bin_vheap_block_size,46422},
                  {bin_old_vheap_size,0},
                  {bin_old_vheap_block_size,46422}]}
Shell got {trace,<0.60.0>,gc_max_heap_size,
                 [{old_heap_block_size,0},
                  {heap_block_size,609},
                  {mbuf_size,145},
                  {recent_size,0},
                  {stack_size,9},
                  {old_heap_size,0},
                  {heap_size,211},
                  {bin_vheap_size,0},
                  {bin_vheap_block_size,46422},
                  {bin_old_vheap_size,0},
                  {bin_old_vheap_block_size,46422}]}
Shell got {trace,<0.60.0>,exit,killed}
---
 erts/doc/src/erl.xml | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

(limited to 'erts/doc/src/erl.xml')

diff --git a/erts/doc/src/erl.xml b/erts/doc/src/erl.xml
index c499fc8081..1bbde7f1e0 100644
--- a/erts/doc/src/erl.xml
+++ b/erts/doc/src/erl.xml
@@ -627,6 +627,34 @@
         <p>Sets the default binary virtual heap size of processes to the size
           <c><![CDATA[Size]]></c>.</p>
       </item>
+      <marker id="+hmax"/>
+      <tag><c><![CDATA[+hmax Size]]></c></tag>
+      <item>
+        <p>Sets the default maximum heap size of processes to the size
+          <c><![CDATA[Size]]></c>. If <c>+hmax</c> is not given, the default is <c>0</c>
+          which means that no maximum heap size is used.
+          For more information, see the documentation of
+          <seealso marker="erlang#process_flag_max_heap_size">
+            <c>process_flag(max_heap_size, MaxHeapSize)</c></seealso>.</p>
+      </item>
+      <marker id="+hmaxel"/>
+      <tag><c><![CDATA[+hmaxel true|false]]></c></tag>
+      <item>
+        <p>Sets whether to send an error logger message for processes that reach
+        the maximum heap size or not. If <c>+hmaxel</c> is not given, the default is <c>true</c>.
+        For more information, see the documentation of
+        <seealso marker="erlang#process_flag_max_heap_size">
+          <c>process_flag(max_heap_size, MaxHeapSize)</c></seealso>.</p>
+      </item>
+      <marker id="+hmaxk"/>
+      <tag><c><![CDATA[+hmaxk true|false]]></c></tag>
+      <item>
+        <p>Sets whether to kill processes that reach the maximum heap size or not. If
+        <c>+hmaxk</c> is not given, the default is <c>true</c>. For more information,
+	see the documentation of
+        <seealso marker="erlang#process_flag_max_heap_size">
+          <c>process_flag(max_heap_size, MaxHeapSize)</c></seealso>.</p>
+      </item>
       <tag><c><![CDATA[+hpds Size]]></c></tag>
       <item>
         <p>Sets the initial process dictionary size of processes to the size
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