[Bug 232800] Processes killed out of swap space

bugzilla-noreply at freebsd.org bugzilla-noreply at freebsd.org
Tue Oct 30 16:49:04 UTC 2018


https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=232800

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

           What    |Removed                     |Added
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                 CC|                            |marklmi26-fbsd at yahoo.com

--- Comment #1 from Mark Millard <marklmi26-fbsd at yahoo.com> ---
[These notes are generated from activity with head. They
in places presume that vm.pageout_oom_seq is available
in 11.2 but that might not be the case. As I understand,
the other aspects of the below notes apply.]

Unfortunately some messages about "out of swap" can be
misnomers, more tied to low free RAM after enough
attempts to gain more free RAM (so after enough time).

Real "out of swap" conditions tend to also have messages
similar to:

Aug  5 17:54:01 sentinel kernel: swap_pager_getswapspace(32): failed

If you are not seeing such messages, then it is likely that
the mount of swap space still free is not the actual thing
driving the kills.

Poor I/O performance for paging and/or swapping can contribute
to the kills happening. But I've no clue if such is an issue
for your context.

The default vm.pageout_oom_seq=12 can be increased
to increase how long a low free RAM condition is tolerated.
(It increases how many attempts to free RAM are made first.)
I assign vm.pageout_oom_seq in /etc/sysctl.conf --but that may
not be the best for your context.

vm.pageout_oom_seq=120 has proved useful. In some extreme
situations (buildworld buildkernel in a low RAM, slow
context, including long I/O latencies) vm.pageout_oom_seq=1024
or more has been used to avoid kills when there was plenty
of swap space.

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