Added watermark_scale_factor tuning

[brettmilford]

Adds a method for determining an appropriate vm.watermark_scale_factor
value for baremetal systems.

Implements: spec memory-fragmentation-tuning

https://review.opendev.org/c/openstack/charm-specs/+/792383

[ajkavanagh]

Thank you for the patch for the additional functionality. I have a few inline comments (please see against the file), and also I think the tests need to be expanded to test the calculate_watermark_scale_factor() function (i.e. only the watermark_scale_factor() function is tested).

It would also be good to actually feed it test fixtures for the /proc/zoneinfo and /proc/meminfo/.

Also, technically, the library still supports Py27 charms, and definitely supports Py35 (xenial) charms.

Thanks.

[brettmilford]

Thanks for the feedback @ajkavanagh.
I've tried implementing your suggestions and improving testing in the latest commit.

[ajkavanagh]

Very much more readable this time; much improved. Unfortunately(!) this let me see some more areas (mostly docstrings) and also a suggestion on improving the code around the searching or proc/zoneinfo.

Many thanks.

[brettmilford]

Hi Alex,
Thanks again for your extensive feedback.
I much prefer your approach to parsing /proc/zoneinfo so I've largely used that.

The heuristics for calculating vm.watermark_scale_factor might change based on this charm spec, and subsequent reviews.
Also currently the unit tests for get_memtotal and get_normal_managed_pages are failing as mock_open doesn't appear to be using read_data as I expected.

[ajkavanagh]

LGTM - let me know if it's ready for merging; you mentioned that there might be a change? Also, thanks very much for your work on this and the changes.

[brettmilford]

@ajkavanagh I think this should now be ready for merging. The associated spec is approved and the tests are passing for me in my env with the latest commit.

[ajkavanagh]

@ajkavanagh I think this should now be ready for merging. The associated spec is approved and the tests are passing for me in my env with the latest commit.

Thanks @brettmilford ; I'm back from leave now and have just kicked off the tests.

[brettmilford]

Hey @ajkavanagh, can you please run the tests again. TY

[niedbalski]

LGTM, minor changes required.

[brettmilford]

@niedbalski @ajkavanagh please take another look, I've added the changes requested. TY

[niedbalski]

Minor change requested.