Date: Thu, 9 Aug 2018 09:44:21 -0700 From: Mark Millard <marklmi@yahoo.com> To: bob prohaska <fbsd@www.zefox.net> Cc: Mark Millard via freebsd-arm <freebsd-arm@freebsd.org>, Mark Johnston <markj@FreeBSD.org> Subject: Re: RPI3 swap experiments ["was killed: out of swap space" with: "v_free_count: 5439, v_inactive_count: 1"] Message-ID: <F61322C1-9B93-48B8-8FAB-269C256F5244@yahoo.com> In-Reply-To: <20180809152152.GC68459@raichu> References: <20180801034511.GA96616@www.zefox.net> <201808010405.w7145RS6086730@donotpassgo.dyslexicfish.net> <6BFE7B77-A0E2-4FAF-9C68-81951D2F6627@yahoo.com> <20180802002841.GB99523@www.zefox.net> <20180802015135.GC99523@www.zefox.net> <EC74A5A6-0DF4-48EB-88DA-543FD70FEA07@yahoo.com> <20180806155837.GA6277@raichu> <20180808153800.GF26133@www.zefox.net> <20180808204841.GA19379@raichu> <20180809065648.GB30347@www.zefox.net> <20180809152152.GC68459@raichu>
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On 2018-Aug-9, at 8:21 AM, Mark Johnston <markj at FreeBSD.org> wrote: > On Wed, Aug 08, 2018 at 11:56:48PM -0700, bob prohaska wrote: >> On Wed, Aug 08, 2018 at 04:48:41PM -0400, Mark Johnston wrote: >>> On Wed, Aug 08, 2018 at 08:38:00AM -0700, bob prohaska wrote: >>>> The patched kernel ran longer than default but OOMA still halted = buildworld around >>>> 13 MB. That's considerably farther than a default build world have = run but less than >>>> observed when setting vm.pageout_oom_seq=3D120 alone. Log files are = at >>>> = http://www.zefox.net/~fbsd/rpi3/swaptests/r337226M/1gbsdflash_1gbusbflash/= batchqueue/ >>>>=20 >>>> Both changes are now in place and -j4 buildworld has been = restarted.=20 >>>=20 >>> Looking through the gstat output, I'm seeing some pretty abysmal = average >>> write latencies for da0, the flash drive. I also realized that my >>> reference to r329882 lowering the pagedaemon sleep period was wrong = - >>> things have been this way for much longer than that. Moreover, as = you >>> pointed out, bumping oom_seq to a much larger value wasn't quite >>> sufficient. >>>=20 >>> I'm curious as to what the worst case swap I/O latencies are in your >>> test, since the average latencies reported in your logs are high = enough >>> to trigger OOM kills even with the increased oom_seq value. When = the >>> current test finishes, could you try repeating it with this patch >>> applied on top? = https://people.freebsd.org/~markj/patches/slow_swap.diff >>> That is, keep the non-default oom_seq setting and modification to >>> VM_BATCHQUEUE_SIZE, and apply this patch on top. It'll cause the = kernel >>> to print messages to the console under certain conditions, so a log = of >>> console output will be interesting. >>=20 >> The run finished with a panic, I've collected the logs and terminal = output at >> = http://www.zefox.net/~fbsd/rpi3/swaptests/r337226M/1gbsdflash_1gbusbflash/= batchqueue/pageout120/slow_swap/ >>=20 >> There seems to be a considerable discrepancy between the wait times = reported >> by the patch and the wait times reported by gstat in the first couple = of=20 >> occurrences. The fun begins at timestamp Wed Aug 8 21:26:03 PDT 2018 = in >> swapscript.log.=20 >=20 > The reports of "waited for swap buffer" are especially bad: during = those > periods, the laundry thread is blocked waiting for in-flight swap = writes > to finish before sending any more. Because the system is generally > quite starved for clean pages that it can reuse, it's relying on swap > I/O to clean more. If that fails, the system eventually has no choice > but to start killing processes (where the time period corresponding to > "eventually" is determined by vm.pageout_oom_seq). Just for reference from=20 = http://www.zefox.net/~fbsd/rpi3/swaptests/r337226M/1gbsdflash_1gbusbflash/= batchqueue/pageout120/slow_swap/swapscript.log is some context for two of the swap buffer messages that gives some information on the timing of the messages and some other activity: Wed Aug 8 22:01:14 PDT 2018 Device 1K-blocks Used Avail Capacity /dev/da0b 1048576 23912 1024664 2% /dev/mmcsd0s3b 1048576 23892 1024684 2% Total 2097152 47804 2049348 2% Aug 8 21:36:13 www syslogd: last message repeated 1 times Aug 8 21:36:13 www kernel: waited 3s for async swap write dT: 10.004s w: 10.000s L(q) ops/s r/s kBps ms/r w/s kBps ms/w d/s kBps = ms/d %busy Name 2 20 1 4 25.5 19 1216 41.4 0 0 = 0.0 29.3 mmcsd0 3 29 1 11 10.8 28 1244 23.9 0 0 = 0.0 18.7 da0 0 0 0 0 0.0 0 3 42.9 0 0 = 0.0 0.4 mmcsd0s2 2 20 1 4 25.6 19 1213 41.5 0 0 = 0.0 29.4 mmcsd0s3 0 0 0 0 0.0 0 3 43.0 0 0 = 0.0 0.4 ufs/rootfs 2 20 1 4 25.6 19 1213 41.6 0 0 = 0.0 29.4 mmcsd0s3b 2 20 1 11 10.9 19 1238 20.6 0 0 = 0.0 18.6 da0b Wed Aug 8 22:01:24 PDT 2018 Device 1K-blocks Used Avail Capacity /dev/da0b 1048576 37284 1011292 4% /dev/mmcsd0s3b 1048576 36920 1011656 4% Total 2097152 74204 2022948 4% Aug 8 21:36:13 www syslogd: last message repeated 1 times Aug 8 21:36:13 www kernel: waited 3s for async swap write dT: 10.002s w: 10.000s L(q) ops/s r/s kBps ms/r w/s kBps ms/w d/s kBps = ms/d %busy Name 0 8 0 0 4.7 8 693 41.7 0 0 = 0.0 12.2 mmcsd0 13 13 0 0 0.0 13 682 132.7 0 0 = 0.0 78.3 da0 0 8 0 0 4.7 8 693 41.8 0 0 = 0.0 12.2 mmcsd0s3 0 8 0 0 4.8 8 693 41.9 0 0 = 0.0 12.3 mmcsd0s3b 5 7 0 0 0.0 7 676 79.5 0 0 = 0.0 40.1 da0b Wed Aug 8 22:01:34 PDT 2018 Device 1K-blocks Used Avail Capacity /dev/da0b 1048576 44680 1003896 4% /dev/mmcsd0s3b 1048576 44132 1004444 4% Total 2097152 88812 2008340 4% Aug 8 21:36:13 www kernel: waited 3s for async swap write Aug 8 22:01:30 www syslogd: last message repeated 1 times Aug 8 22:01:41 www kernel: waited 10s for async swap write Aug 8 22:01:41 www kernel: waited 6s for swap buffer Aug 8 22:01:41 www kernel: waited 13s for async swap write Aug 8 22:01:41 www kernel: waited 3s for swap buffer Aug 8 22:01:41 www kernel: waited 12s for async swap write Aug 8 22:01:41 www kernel: waited 10s for async swap write Aug 8 22:01:41 www kernel: waited 3s for async swap write dT: 10.001s w: 10.000s L(q) ops/s r/s kBps ms/r w/s kBps ms/w d/s kBps = ms/d %busy Name 0 2 1 26 3.4 1 17 3.8 0 0 = 0.0 0.9 mmcsd0 0 4 3 61 3.8 2 70 5.7 0 0 = 0.0 1.7 da0 0 2 1 26 3.5 1 17 3.9 0 0 = 0.0 0.9 mmcsd0s3 0 1 0 0 0.0 1 17 4.0 0 0 = 0.0 0.4 mmcsd0s3a 0 1 1 26 3.5 0 0 0.0 0 0 = 0.0 0.5 mmcsd0s3b 0 2 2 54 3.8 0 0 0.0 0 0 = 0.0 0.9 da0b 0 2 0 7 4.3 1 70 5.8 0 0 = 0.0 0.8 da0d Wed Aug 8 22:01:51 PDT 2018 Device 1K-blocks Used Avail Capacity /dev/da0b 1048576 46156 1002420 4% /dev/mmcsd0s3b 1048576 45480 1003096 4% Total 2097152 91636 2005516 4% Aug 8 22:01:41 www kernel: waited 10s for async swap write Aug 8 22:01:41 www kernel: waited 3s for async swap write dT: 10.002s w: 10.000s L(q) ops/s r/s kBps ms/r w/s kBps ms/w d/s kBps = ms/d %busy Name 0 8 7 251 3.4 0 8 2.6 0 0 = 0.0 2.5 mmcsd0 0 9 7 186 4.2 2 77 7.4 0 0 = 0.0 3.6 da0 0 8 7 251 3.5 0 8 2.6 0 0 = 0.0 2.6 mmcsd0s3 0 0 0 0 0.0 0 8 2.7 0 0 = 0.0 0.1 mmcsd0s3a 0 7 7 251 3.5 0 0 0.0 0 0 = 0.0 2.5 mmcsd0s3b 0 7 7 184 4.2 0 0 0.0 0 0 = 0.0 2.7 da0b 0 2 0 2 4.6 2 76 7.5 0 0 = 0.0 0.9 da0d > Based on these latencies, I think the system is behaving more or less = as > expected from the VM's perspective. I do think the default oom_seq = value > is too low and will get that addressed in 12.0. =3D=3D=3D Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar)
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