Date: Sat, 15 Sep 2018 00:11:48 -0700 From: Mark Millard <marklmi@yahoo.com> To: Trev <freebsd-arm@sentry.org> Cc: freebsd-arm@freebsd.org Subject: Re: RPI3 swap experiments (r338342 with vm.pageout_oom_seq="1024" and 6 GB swap) Message-ID: <FC904C65-D9A7-46B6-B21D-BCEAB7DCFDA2@yahoo.com> In-Reply-To: <8fd79c5e-4998-274a-6457-ac2a6bf939bb@sentry.org> References: <20180815013612.GB51051@www.zefox.net> <CANCZdfoB_AcidFpKT_ZmZWUFnmC4Bw55krK%2BMqEmmj=f9KMQ2Q@mail.gmail.com> <20180815225504.GB59074@www.zefox.net> <20180901230233.GA42895@www.zefox.net> <20180906003829.GC818@www.zefox.net> <FB333A71-47D8-4038-9983-116DA80FC952@yahoo.com> <20180906051520.GB3482@www.zefox.net> <059D2FED-6E7C-4FEF-8807-8D4A0D0B3E26@yahoo.com> <20180906155858.GA5980@www.zefox.net> <075BD4BB-CAFB-4C9B-809A-10901522D1ED@yahoo.com> <20180915050842.GA65045@www.zefox.net> <8fd79c5e-4998-274a-6457-ac2a6bf939bb@sentry.org>
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On 2018-Sep-14, at 11:18 PM, Trev <freebsd-arm at sentry.org> wrote: > bob prohaska wrote on 15/09/2018 15:08: >> There were many spurious "indefinite wait" and [...] warnings on the = console, [Bob did not say if he had Mark Johnston's reporting patches in place or not.] > Those warnings are not actually spurious, rather indicative of = significant i/o delays: >=20 > https://www.freebsd.org/doc/en/books/faq/troubleshoot.html#idp59131080 >=20 > What does the error swap_pager: indefinite wait buffer: mean? >=20 > This means that a process is trying to page memory to disk, and the = page attempt has hung trying to access the disk for more than 20 = seconds. It might be caused by bad blocks on the disk drive, disk = wiring, cables, or any other disk I/O-related hardware. If the drive = itself is bad, disk errors will appear in /var/log/messages and in the = output of dmesg. Otherwise, check the cables and connections. =46rom what I can see from: http://www.zefox.net/~fbsd/rpi3/swaptests/r338572/1.8gbsd/swapscript.log no I/O errors were reported. ("swap_pager: indefinite wait buffer:" messages do show.) microsd card slots do not have cables or cable-connections involved generally: what would be analogous would be far harder to do anything about. =46rom what I've seen the I/O for the paging (mixed with the other I/O activity) can potentially queue enough data to be paged out that, under normal operation, the microsd card would take more than 20 seconds to write it all out. Say, 10 MiBytes/sec * 20 sec =3D 200 MiByte, to give ball park figures that likely are on the large side as I understand. (Paging is not sequential and reads/writes are mixed.) So if the time waiting in the queue of pending I/O is counted in that 20 seconds for the data in question, that alone might lead to message for the data that is far from the front of the queue when it is first added, no errors involved. But, that is an "if": I do not know just what starts the 20 second measurement. It looks like the distinct swap_pager messages for the ultra plus only example were: $ grep swap_pager: ~/Downloads/swapscript_rpi3_ultra_plus.log | sort | = uniq Sep 11 07:12:52 www kernel: swap_pager: indefinite wait buffer: bufobj: = 0, blkno: 88445, size: 4096 Sep 11 07:13:01 www kernel: swap_pager: indefinite wait buffer: bufobj: = 0, blkno: 464452, size: 12288 Sep 11 07:13:56 www kernel: swap_pager: indefinite wait buffer: bufobj: = 0, blkno: 11922, size: 4096 Sep 11 11:34:08 www kernel: swap_pager: indefinite wait buffer: bufobj: = 0, blkno: 295286, size: 8192 Sep 11 11:34:08 www kernel: swap_pager: indefinite wait buffer: bufobj: = 0, blkno: 371269, size: 4096 Sep 11 12:48:23 www kernel: swap_pager: indefinite wait buffer: bufobj: = 0, blkno: 408974, size: 4096 Sep 11 13:09:07 www kernel: swap_pager: indefinite wait buffer: bufobj: = 0, blkno: 293166, size: 8192 Sep 11 13:10:19 www kernel: swap_pager: indefinite wait buffer: bufobj: = 0, blkno: 226334, size: 8192 =3D=3D=3D Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar)
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