src: extend `HeapStatistics` with new fields

src: Add does_zap_garbage, malloced_memory and
peak_malloced_memory to v8 HeapStatistics

Following https://github.com/nodejs/code-and-learn/issues/56 I
have exposed does_zap_garbage to HeapStatistics.
The other fields, malloced_memory and peak_malloced_memory don't
seem to be in the current version of v8 in master.

PR-URL: https://github.com/nodejs/node/pull/8610
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

1 files changed, 13 insertions, 1 deletions

diff --git a/doc/api/v8.md b/doc/api/v8.md
index 82169d0486..8cec6bdfdf 100644
--- a/doc/api/v8.md
+++ b/doc/api/v8.md
@@ -22,6 +22,15 @@ Returns an object with the following properties:
 * `total_available_size` {number}
 * `used_heap_size` {number}
 * `heap_size_limit` {number}
+* `malloced_memory` {number}
+* `peak_malloced_memory` {number}
+* `does_zap_garbage` {number}
+
+`does_zap_garbage` is a 0/1 boolean, which signifies whether the `--zap_code_space`
+option is enabled or not. This makes V8 overwrite heap garbage with a bit
+pattern. The RSS footprint (resident memory set) gets bigger because it
+continuously touches all heap pages and that makes them less likely to get
+swapped out by the operating system.
 
 For example:
 
@@ -32,7 +41,10 @@ For example:
   total_physical_size: 7326976,
   total_available_size: 1152656,
   used_heap_size: 3476208,
-  heap_size_limit: 1535115264
+  heap_size_limit: 1535115264,
+  malloced_memory: 16384,
+  peak_malloced_memory: 1127496,
+  does_zap_garbage: 0
 }
 ```