Please link to the Linux MM team's wiki which describes the problem and why they haven't already fixed it:

• https://linux-mm.org/AdvancedPageReplacement (and related pages on that wiki)

Also, your alternate methods shows you to do it using raw cgroups.
Please mention that systemd 231 users can easily get the same results on a per-unit basis with MemoryHigh=.
For example,

    # my-update-script.service
    [Service]
    Type=oneshot
    Exec=/usr/local/bin/my-update-script
    MemoryHigh=128M

The exact MemoryHigh= is not important -- it should be bigger than the script's typical peak usage, and significantly lower than your total RAM.

PS: MemoryHigh= uses the second generation of cgroup stuff. IIRC your README.md is still documenting the first-generation cgroup stuff? I think the details are buried in https://www.kernel.org/doc/Documentation/cgroup-v2.txt but I haven't gone digging for a while.