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doc: Add useful V8 option section #32262

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doc: add useful v8 option section
nimit95 Mar 14, 2020
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doc: add useful v8 option section
nimit95 Mar 14, 2020
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Update doc/api/cli.md
nimit95 Mar 17, 2020
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Update doc/api/cli.md
nimit95 Mar 17, 2020
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doc: add to cli.md V8 options
nimit95 Mar 17, 2020
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doc: fix trailing whitespace in cli.md
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doc: update cli.md for fixes
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fix language cli.md
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fix example formatting
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doc: add useful v8 option section 
This adds new section for v8 options and --max-old-space-size
Fixes: #32252
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nimit95 committed Mar 14, 2020
commit 0090f54ea77bae15547585c0dbfcf4f229ce5c01
16 changes: 16 additions & 0 deletions doc/api/cli.md
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Expand Up @@ -1180,6 +1180,8 @@ V8 options that are allowed are:
`--perf-basic-prof-only-functions`, `--perf-basic-prof`,
`--perf-prof-unwinding-info`, and `--perf-prof` are only available on Linux.

### Useful v8 Options
##
### `NODE_PATH=path[:…]`
<!-- YAML
added: v0.1.32
Expand Down Expand Up @@ -1385,6 +1387,20 @@ threadpool by setting the `'UV_THREADPOOL_SIZE'` environment variable to a value
greater than `4` (its current default value). For more information, see the
[libuv threadpool documentation][].

## Useful v8 Options

These are v8 options and fall outside Node.js' responsibility.
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@sam-github sam-github Mar 16, 2020

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These are v8 options and fall outside Node.js' responsibility.
V8 has CLI options. Any V8 CLI option that is provided to `node` will be passed on to V8 to handle. V8's options have _no stability guarantee_. The V8 team themselves don't consider them to be part of their formal API, and reserve the right to change them at any time. The Node.js team does not consider them covered by the Node.js stability guarantees. Many of the V8 options are of interest only to V8 developers. Despite this, there is a small set of V8 options that are widely applicable to Node.js, and they are documented here.

I think we should say something like the above.


V8 options that are allowed are:
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@mscdex mscdex Mar 14, 2020

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I think this should either be removed completely or at least reworded. Node does not restrict the V8 options that can be passed on the command line.

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@nimit95 nimit95 Mar 17, 2020

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There is another place in the document mentioning the same thing.


### `--max-old-space-size`
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@sam-github sam-github Mar 16, 2020

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### `--max-old-space-size`
### `--max-old-space-size=SIZE` (in Mbytes)


Sets the max memory size of V8 old memory section. As memory consumption approaches the limit, V8 will spend more time on garbage collection in an effort to free unused memory.

On a machine with 2GB of memory it suggested to set 1.5GB to leave some memory for other uses and avoid swapping.
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@jasnell jasnell Mar 16, 2020

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Suggested change
Sets the max memory size of V8 old memory section. As memory consumption approaches the limit, V8 will spend more time on garbage collection in an effort to free unused memory.
On a machine with 2GB of memory it suggested to set 1.5GB to leave some memory for other uses and avoid swapping.
Sets the max memory size of V8 old memory section. As memory
consumption approaches the limit, V8 will spend more time on
garbage collection in an effort to free unused memory.
On a machine with 2GB of memory it suggested to set 1.5GB to
leave some memory for other uses and avoid swapping.

nit: need to wrap lines at <= 80 chars


E.g. `node --max-old-space-size=1536 index.js`
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@Trott Trott Mar 30, 2020

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Optional nit: Delete this line.

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@nimit95 nimit95 Apr 3, 2020 •
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I personally feel an example helps a lot when being introduced to a flag. It clearly shows how to pass an argument. @Trott

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@Trott Trott Apr 5, 2020

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I personally feel an example helps a lot when being introduced to a flag

If we want to provide an example, it should conform with the formatting of the other examples provided elsewhere in the doc. Otherwise, each entry is inventing its own example formatting, and we definitely do not want that. The existing format is more useful than this as it provides context, such as what the anticipated output might look like. So, this example might show the error one might get if running without the flag, then show the command succeeding with the flag.

(That said, most of our entries do not contain examples and that seems appropriate in this document.)

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@nimit95 nimit95 Apr 6, 2020

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Totally agree with your point, Can you point me to some of the correct existing formats?
What I see a mixture of formats, some given below

  1. node --name-of-flag index.mjs
  2. node --name-of-flag

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@Trott Trott Apr 6, 2020

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I don't mean the format of the command itself. I mean the markdown formatting that denotes an example.

```console
$ node --cpu-prof index.js
$ ls *.cpuprofile
CPU.20190409.202950.15293.0.0.cpuprofile
```

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@nimit95 nimit95 Apr 8, 2020 •
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@Trott can you check out the formatting once now.


[`--openssl-config`]: #cli_openssl_config_file
[`Buffer`]: buffer.html#buffer_class_buffer
[`SlowBuffer`]: buffer.html#buffer_class_slowbuffer
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