Re: armv6/armv7/aarch64 vs. FreeBSD images (retitled from an arch reply, moving to freebsd-arm list)

On Dec 13, 2022, at 22:45, Mark Millard <marklmi@yahoo.com> wrote:

> Julian H. Stacey <jhs_at_berklix.com> wrote on
> Date: Wed, 14 Dec 2022 02:22:10 UTC :
> 
>> . . .
> 
>> I previously had some kind of a 3B, & now have a "Pi 3 Model B+",
>> but have not got beyond booting images, starting to customise /etc/
>> & then it crashes yet again, needing yet another dd, & repeat,
>> Being certain one is using the right image would be nice.
> 
> This does not sound normal at all. I expect something more
> specific to your context is involved.
> 
>> My notes: http://www.berklix.org/~jhs/pi/#images
> 
> I'll look at the notes separately, possibly not tonight.
> 

Note: I presume use of an aarch64 FreeBSD, not armv7
or armv6. Otherwise some things would be different
below, such as via tighter constraints on swap space
sizes for 1 GiByte of RAM.

Quoting http://www.berklix.org/~jhs/pi/#images :

QUOTE
  pid 17 (sh), jid @, uid 8, was killed: failed to reclain menory
END QUOTE

This is the FreeBSD kernel complaining about the configuration
not well matching the RPi3B+ workload. In essence, it was unable
to achieve it targeted minimum amount of free RAM in the sort of
time frame (really: effort) it is configured for. Depending on
what you do, the FreeBSD defaults do not work well for 1 GiByte
of RAM. Swap space alone is insufficient because FreeBSD does
not swap out processes that stay runnable. Just one process that
stays runnable using a working set that is as large as the fits
RAM for overall operation will lead to such "failed to reclaim
memory" kills.

But, if you are getting this, you will almost certainly need
a non-trivial swap space anyway.

I have a starting point to recommend, configuring some
settings. As I've no detailed clue for your context,
I'll just provide the general description.


A) I recommend a swap space something like shown in
the below (from gpart show output):

=>        40  1953525088  da0  GPT  (932G)
          40      532480    1  efi  (260M)
      532520        2008       - free -  (1.0M)
      534528     7340032    2  freebsd-swap  (3.5G)
. . .
    67643392  1740636160    5  freebsd-ufs  (830G)
  1808279552   145245576       - free -  (69G)

This size (3.5 GiBytes or so) is somewhat below
were FreeBSD starts to complain about potential
mistuning from a large swap space, given the 1
GiByte of RAM. (I boot the same boot media on a
variety of machines and have other swap partitions
to match up with RAM sizes. But I omitted showing
them.)

It is easy to have things like buildworld or
building ports end up with individual processes
that are temporarily bigger than the 1 GiByte RAM.
Getting multiple cores going can also lead to
not fitting and needing to page.

I'll note that I normally use USB3 NVMe media that
also works with USB2 ports. My alternate is USB3
SSD media that works with USB2 ports. I avoid
spinning rust and microsd cards. This limits what
I can usefully comment on for some aspects of
configuration related to the alternatives.


B) /boot/loader.conf content:

#
# Delay when persistent low free RAM leads to
# Out Of Memory killing of processes:
vm.pageout_oom_seq=120
#
# For plunty of swap/paging space (will not
# run out), avoid pageout delays leading to
# Out Of Memory killing of processes:
vm.pfault_oom_attempts=-1
#
# For possibly insufficient swap/paging space
# (might run out), increase the pageout delay
# that leads to Out Of Memory killing of
# processes (showing defaults at the time):
#vm.pfault_oom_attempts= 3
#vm.pfault_oom_wait= 10
# (The multiplication is the total but there
# are other potential tradoffs in the factors
# multiplied, even for nearly the same total.)

If use of vm.pfault_oom_attempts=-1 is going to
be inappropriate, I do not have background with
figuring out a good combination of settings for
vm.pfault_oom_attempts and vm.pfault_oom_wait .

I'll note that vm.pageout_oom_seq is not a time
--more like how many insufficient tries to
reclaim RAM happen in sequence before an OOM
kill is started (effort). 120 is 10 times the
default. While nothing disables such criteria,
larger figures can be used if needed. (I've
never had to but others have.)


C) /etc/sysctl.conf content:

#
# Together this pair avoids swapping out the process kernel stacks.
# This avoids one way for processes for interacting with the system
# from ending up being hung-up.
vm.swap_enabled=0
vm.swap_idle_enabled=0


D) I strictly avoid having tmpfs complete for RAM
in this kind of context. tmpfs use just makes
avoiding "failed to reclaim memory" more difficult
to avoid. (As various folks have run into despite
having vastly more RAM than an RPi3B+.) So my
/usr/local/etc/poudriere.conf has:

USE_TMPFS=no

There are examples, like building rust, where
anything but "no" or "data" leads to huge 10
GiByte+ tmpfs spaces for poudriere's build
activity. Not a good match to an RPi3B+ .


That is it for the recommendations of a starting
point configuration.

With such measures, I've been able to have poudriere
with -j4 but also using ALLOW_MAKE_JOBS= without using
the likes of MAKE_JOBS_NUMBER limiting it. (So the
load average could be around 16 a fair amount of the
time but still not get "failed to reclaim memory"
kills.)

Note: I'm not claiming above that -j4 is the best
setting to use from, say, a elapsed time point of
view for my poudriere bulk activity.

I'll not volunteer anyone specific, but there are
folks that have reported using RPi3B+'s on the lists,
mostly via asking some question related to system
operation. So you might be able to ask for
information from anyone that really has an RPi3B+
in use, possibly describing the context that gives
rise to the question(s).

===
Mark Millard
marklmi at yahoo.com