I suggest caution in raising vm.v_free_min, at least on 11.2-RELEASE
systems with less RAM. I tried "65536" (256MB) on a 4GB mini-server, with
vfs.zfs.arc_max of 2.5GB. Bad things happened when the cron daemon merely
tried to run `periodic daily`.
A few more details - ARC was mostly full, and "bad things" was 1:
`pagedaemon` seemed to be thrashing memory - using 100% of CPU, with
little disk activity, and 2: many normal processes seemed unable to run.
The latter is probably explained by `man 3 sysctl` (see entry for
"VM_V_FREE_MIN").
On Mon, 18 Mar 2019, Pete French wrote:
On 17/03/2019 21:57, Eugene Grosbein wrote:
I agree. Recently I've found kind-of-workaround for this problem:
increase vm.v_free_min so when "FREE" memory goes low,
page daemon wakes earlier and shrinks UMA (and ZFS ARC too) moving some
memory
from WIRED to FREE quick enough so it can be re-used before bad things
happen.
But avoid increasing vm.v_free_min too much (e.g. over 1/4 of total RAM)
because kernel may start behaving strange. For 16Gb system it should be
enough
to raise vm.v_free_min upto 262144 (1GB) or 131072 (512M).
This is not permanent solution in any way but it really helps.
Ah, thats very interesting, thankyou for that! I;ve been bitten by this issue
too in the past, and it is (as mentioned) much improved on 12, but the act it
could still cause issues worries me.
-pete.
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