[Bug 231457] Out of swap space on ZFS

bugzilla-noreply at freebsd.org bugzilla-noreply at freebsd.org
Mon Oct 1 19:13:19 UTC 2018


https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=231457

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

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

--- Comment #6 from Mark Millard <marklmi26-fbsd at yahoo.com> ---
As I understand any conditions that lead to sustained low
free RAM via pressure from one or more processes that keep
active RAM usage high leads to killing of processes to free
memory. The default vm.pageout_oom_seq=12 can be increased
to increase how long the 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 .

FreeBSD does not swap out processes that stay active. This
is documented in the book published by McKusic, Neville-Neil,
and Watson (2nd edition, last names listed). So if one or more
keep active RAM use high, free RAM use tends to stay low.

There can be lots of swap available and the process
killing can still happen. The console log messages
produced for this case is very misleading via referencing
out of swap instead of referencing a sustained period of
low free RAM.

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

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

On small board computers such as ARM boards I've been
using vm.pageout_oom_seq=120 and one person with storage
devices with I/O latency problems used something like
vm.pageout_oom_seq=1024 to allow -j4 buildworld buildkernel
to work. (No attempt at approximating the smallest value
that would have worked.) There was a long 2018 Jun. through
Sep. freebsd-arm list exchange under various subjects that
eventually exposed this vm.pageout_oom_seq control and
FreeBSD's swapping criteria that I noted above.

This does not address why Free RAM is low over a sustained
period, it just makes the system more tolerant of such. It
could be that there are also other mechanisms that do not
involve vm.pageout_oom_seq .

-- 
You are receiving this mail because:
You are the assignee for the bug.


More information about the freebsd-bugs mailing list