Date: Mon, 18 Mar 2019 09:37:14 -0400 (EDT) From: Walter Cramer <wfc@mintsol.com> To: Pete French <petefrench@ingresso.co.uk> Cc: freebsd-stable@freebsd.org Subject: Re: Observations from a ZFS reorganization on 12-STABLE Message-ID: <20190318091431.W52549@mulder.mintsol.com> In-Reply-To: <2baf16fd-3767-1dda-d519-995f7ebaf0cb@ingresso.co.uk> References: <58eb1994-41bd-cd22-be66-0024bcbc36e6@denninger.net> <e5c648b4-ba73-5d3a-2924-be4d52e4c267@grosbein.net> <2baf16fd-3767-1dda-d519-995f7ebaf0cb@ingresso.co.uk>
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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. > _______________________________________________ > freebsd-stable@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org"
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