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doc: add new useful V8 option
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Add the `--max_semi_space_size` flag into useful V8 option.

Fixes: #42511

PR-URL: #42575
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>
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JialuZhang-intel authored and targos committed Jul 12, 2022
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Expand Up @@ -2034,6 +2034,32 @@ On a machine with 2 GiB of memory, consider setting this to
$ node --max-old-space-size=1536 index.js
```

### `--max-semi-space-size=SIZE` (in megabytes)

Sets the maximum [semi-space][] size for V8's [scavenge garbage collector][] in
MiB (megabytes).
Increasing the max size of a semi-space may improve throughput for Node.js at
the cost of more memory consumption.

Since the young generation size of the V8 heap is three times (see
[`YoungGenerationSizeFromSemiSpaceSize`][] in V8) the size of the semi-space,
an increase of 1 MiB to semi-space applies to each of the three individual
semi-spaces and causes the heap size to increase by 3 MiB. The throughput
improvement depends on your workload (see [#42511][]).

The default value is 16 MiB for 64-bit systems and 8 MiB for 32-bit systems. To
get the best configuration for your application, you should try different
max-semi-space-size values when running benchmarks for your application.

For example, benchmark on a 64-bit systems:

```bash
for MiB in 16 32 64 128; do
node --max-semi-space-size=$MiB index.js
done
```

[#42511]: https://github.com/nodejs/node/issues/42511
[Chrome DevTools Protocol]: https://chromedevtools.github.io/devtools-protocol/
[CommonJS]: modules.md
[ECMAScript module loader]: esm.md#loaders
Expand All @@ -2059,6 +2085,7 @@ $ node --max-old-space-size=1536 index.js
[`NODE_OPTIONS`]: #node_optionsoptions
[`NO_COLOR`]: https://no-color.org
[`SlowBuffer`]: buffer.md#class-slowbuffer
[`YoungGenerationSizeFromSemiSpaceSize`]: https://chromium.googlesource.com/v8/v8.git/+/refs/tags/10.3.129/src/heap/heap.cc#328
[`dns.lookup()`]: dns.md#dnslookuphostname-options-callback
[`dns.setDefaultResultOrder()`]: dns.md#dnssetdefaultresultorderorder
[`dnsPromises.lookup()`]: dns.md#dnspromiseslookuphostname-options
Expand All @@ -2078,6 +2105,8 @@ $ node --max-old-space-size=1536 index.js
[libuv threadpool documentation]: https://docs.libuv.org/en/latest/threadpool.html
[remote code execution]: https://www.owasp.org/index.php/Code_Injection
[running tests from the command line]: test.md#running-tests-from-the-command-line
[scavenge garbage collector]: https://v8.dev/blog/orinoco-parallel-scavenger
[security warning]: #warning-binding-inspector-to-a-public-ipport-combination-is-insecure
[semi-space]: https://www.memorymanagement.org/glossary/s.html#semi.space
[timezone IDs]: https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
[ways that `TZ` is handled in other environments]: https://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html

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