[Bug 257314] FBSD 13 crash after some KDE parts crash supposing out of swap space

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=257314

Mark Millard <marklmi26-fbsd@yahoo.com> changed:

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                 CC|                            |marklmi26-fbsd@yahoo.com

--- Comment #3 from Mark Millard <marklmi26-fbsd@yahoo.com> ---
(In reply to Graham Perrin from comment #1)

Various "out of swap space" kill messages are misnomers,
unfortunately.

Only if there were also the following sorts of messages are
the indications correct:

swap_pager: out of swap space
swp_pager_getswapspace(3): failed

Other causes of "out of swap space" kill messages include:

Sustained low free RAM (via 1 more more stays-runnable processes).
A sufficiently delayed pageout.
The swap blk uma zone was exhausted.
The swap pctrie uma zone was exhausted.

The first two have loader tunable's that make the system
tolerate conditions for longer, potentially much longer
before starting kills. (The values shown are generally
only examples that were sufficient for some specific
context.)

I recommend trying the following sorts of thing in, say,
/boot/loader.conf and booting with the settings used:

#
# 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.)


I'm not aware of anything to adjust for either
of:

The swap blk uma zone was exhausted.
The swap pctrie uma zone was exhausted.

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