Bug#946694: systemd: 'ControlGroupAttribute=memory.swappiness 0' does nothing

[Charles Samuels]

Package: systemd
Version: 241-7~deb10u2
Severity: normal

Dear Maintainer,

I have a service with:
[Service]
ControlGroupAttribute=memory.swappiness 0

But when I look at the process's entry in
/sys/fs/cgroup/memory/system.slice/servicename.service/memory.swappiness
I see it has the default swappiness of 60.
     
What's more is that I can't do this:
ExecStartPost=/bin/sh -c "echo 0 > /sys/fs/cgroup/memory/system.slice/
servicename.service/memory.swappiness"

because ExecStartPost is apparently run before the cgroup is established.
This is really awful behavior because I can't spawn essential services that 
rely on not getting swapped out on my very busy server. This deeply affects 
performance of my servers.

Debian Release: 10.2
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)
   
Kernel: Linux 4.19.0-6-amd64 (SMP w/32 CPU cores)
Kernel taint flags: TAINT_WARN, TAINT_SOFTLOCKUP
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), 
LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages systemd depends on:
ii  adduser          3.118
ii  libacl1          2.2.53-4
ii  libapparmor1     2.13.2-10
ii  libaudit1        1:2.8.4-3
ii  libblkid1        2.33.1-0.1
ii  libc6            2.28-10
ii  libcap2          1:2.25-2
ii  libcryptsetup12  2:2.1.0-5+deb10u2
ii  libgcrypt20      1.8.4-5
ii  libgnutls30      3.6.7-4
ii  libgpg-error0    1.35-1
ii  libidn11         1.33-2.2
ii  libip4tc0        1.8.2-4
ii  libkmod2         26-1
ii  liblz4-1         1.8.3-1
ii  liblzma5         5.2.4-1
ii  libmount1        2.33.1-0.1
ii  libpam0g         1.3.1-5
ii  libseccomp2      2.3.3-4
ii  libselinux1      2.8-1+b1
ii  libsystemd0      241-7~deb10u2
ii  mount            2.33.1-0.1
ii  util-linux       2.33.1-0.1

Versions of packages systemd recommends:
ii  dbus            1.12.16-1
ii  libpam-systemd  241-7~deb10u2

Versions of packages systemd suggests:
pn  policykit-1        <none>
ii  systemd-container  241-7~deb10u2

Versions of packages systemd is related to:
pn  dracut           <none>
ii  initramfs-tools  0.133+deb10u1
ii  udev             241-7~deb10u2

-- no debconf information