doc: note synchronous part of child_process.spawn

If an application has a large RSS (GB), jorangreef observed that child_process.spawn will block the event loop for ms-s. This is surprising behavior and merits documentation. Refs: #14917 PR-URL: #21234 Reviewed-By: Gireesh Punathil <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Ben Noordhuis <[email protected]> Reviewed-By: Trivikram Kamat <[email protected]>
nodejs · Jun 22, 2018 · 8a997a5 · 8a997a5
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diff --git a/doc/api/child_process.md b/doc/api/child_process.md
@@ -652,6 +652,12 @@ child registers an event handler for the [`'disconnect'`][] event
 or the [`'message'`][] event. This allows the child to exit
 normally without the process being held open by the open IPC channel.*
 
+On UNIX-like operating systems, the [`child_process.spawn()`][] method
+performs memory operations synchronously before decoupling the event loop
+from the child. Applications with a large memory footprint may find frequent
+[`child_process.spawn()`][] calls to be a bottleneck. For more information,
+see [V8 issue 7381](https://bugs.chromium.org/p/v8/issues/detail?id=7381).
+
 See also: [`child_process.exec()`][] and [`child_process.fork()`][].
 
 ## Synchronous Process Creation