node only using half of the available memory

* **Version**: 12.19.0 * **Platform**: Debian Buster * **Subsystem**: ### What steps will reproduce the bug? 1. Start a container with limited memory (something like `docker run --rm -it --memory=1G --memory-swap=1G node:12.19.0-buster-slim bash` 2. Inspect heap size (`node -e 'const v8 = require("v8"); console.log(v8.getHeapStatistics());'`) ### How often does it reproduce? Is there a required condition? 100% ### What is the expected behavior? `node` would use all available memory ### What do you see instead? `node` is only using half of the memory, so we either need to give the container twice as much memory as we really want it to use (which is problematic) or also specify `--max-old-space-size` in addition to controlling the container which means we have to keep 2 different settings in sync and that's a big pain ### Additional information It appears that it was [changed here](https://github.com/nodejs/node/pull/25576#issuecomment-455737693), and only using half of memory makes sense when running on a system with multiple process, but when running in a docker container, using all of the memory allocated to the container makes more sense