The minimal memory reserved parameter vm.min_free_kbytes should be
between 1-3% according to RedHat.
However, the kernel by default reserves around 3MB (e.g. only 3285 on a
32-bit Raspberry Pi 4 2GB installation). This seems to be too low for
network intensive applications such as ours: Under memory pressure
"page allocation failure" on various orders have been observed.
Raspberry Pi OS uses a fixed value of 16MB. Follow this setting for now.
Note: We cannot set this globally for Home Assistant: x86-64 machines
can have quite a bit more memory, which also requires increased
min_free_kbytes parameter. ODROID-N2 on the other hand uses transparent
huge pages: If enabled, the kernel requires higher min_free_kbytes
values, and sets those also by default (e.g. on ODROID-N2+ with 4GB
memory its set to 22528 by default).
systemd-udevd substitutes variables starting with $ in the PROGRAM
argument. If a shell variable is to be used, two $ need to be used to
escape properly. This fixes three instances of the following warning:
Invalid value "..." for PROGRAM (char 58: invalid substitution type), ignoring, but please fix it.
The to symlink serial0/1 currently might apply to the first or second
ttyAMAX instance. In downstream, a patch makes sure that the first
PL011 is always ttyAMA0. However, upstream the numbering depends on the
UART alias, which leads to the first PL011 being ttyAMA1.
Check the actual iobase too to make sure we are dealing with the first
PL011 instance.
See also:
05cfe136f7 (diff-2678c183f503319c8d8c09c818af789a)
