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, 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

Start by reproducing the issue with the provided docker run command and the node -e v8.getHeapStatistics() check. Trace how Node.js determines the container memory limit and compare that value with the expected 1G allocation; done means the runtime sizes the heap appropriately without requiring a separate --max-old-space-size setting.