Fix memory limit check bytes to GB conversion

[1pkg]

Motivation/summary

This PR closed the issue #13837, by fixing the bytes to GB conversion in the fallback memory check.

Checklist

Update CHANGELOG.asciidoc

• Documentation has been updated

For functional changes, consider:

• Is it observable through the addition of either logging or metrics?
• Is its use being published in telemetry to enable product improvement?
• Have system tests been added to avoid regression?

How to test these changes

The easiest way to test this change is to create a custom cgroup with a memory limit that is larger than the total system memory, then start apm-server binary with the created cgroup. Observer APM Server logs for "cgroup memory limit exceed available memory, falling back to the total system memory".

cgcreate  -g memory:apm_test
cgget -r memory.limit_in_bytes=10737418240 /apm_test
cgexec -g memory:apm_test ./apm-server run

Related issues

Changelog

==== Bug fixes

• Fix memory limit fallback check bytes to GB conversion {pull}13838[13838]

[kruskall]

LGTM! Thanks for the fix! 🙇

[marclop]

Thanks for the fix and tidying the code!

[carsonip]

nice catch!
non-blocker: is this something that can be covered by tests? Otherwise, the PR test instructions are clear enough should be fine.

[carsonip]

changes lgtm. Thanks for the tests.

Could you remove the changelog? It will be added back later in the release process. Sorry if I didn't express that clearly in the earlier comment.

[carsonip]

I'll approve it first so you can merge it right away after removing the changelog (if github allows you to do that)

[kruskall]

Tested with systemd-run --scope -p MemoryMax=200G --use ./apm-server -e

{"log.level":"info","log.logger":"beater","log.origin":{"function":"github.com/elastic/apm-server/internal/beater.processMemoryLimit","file.name":"beater/beater.go","file.line":1027},"message":"cgroup memory limit exceed available memory, falling back to the total system memory","service.name":"apm-server","ecs.version":"1.6.0"}