Date: Sun, 21 Nov 2021 14:13:10 -0800 From: Mark Millard via freebsd-stable <freebsd-stable@freebsd.org> To: FreeBSD-STABLE Mailing List <freebsd-stable@freebsd.org>, "freebsd-arm@freebsd.org" <arm@freebsd.org> Subject: tmpfs use and "stress --hdd ? --hdd-bytes ??G" can lead to hung up system (16 Cortex-A72's system example) Message-ID: <B57099EE-5DE7-4944-ADEE-BAD65E46F375@yahoo.com> References: <B57099EE-5DE7-4944-ADEE-BAD65E46F375.ref@yahoo.com>
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Context: # uname -apKU FreeBSD CA72_16Gp_ZFS 13.0-STABLE FreeBSD 13.0-STABLE #13 = stable/13-n248062-109330155000-dirty: Sat Nov 13 23:55:14 PST 2021 = root@CA72_16Gp_ZFS:/usr/obj/BUILDs/13S-CA72-nodbg-clang/usr/13S-src/arm64.= aarch64/sys/GENERIC-NODBG-CA72 arm64 aarch64 1300520 1300520 (It is a non-debug kernel build, but with symbols.) 64 GiBytes of RAM Swap: 251904Mi Total 16-core Cortex-A72 system (HoneyComb) root-on-ZFS on Optane media in the PCIe slot The following sort of sequence using tmpfs tends to hangs up the system long before the maximum swap usage would happen: # mount -ttmpfs tmpfs /mnt # cd /mnt # stress --hdd 16 --hdd-bytes 16G The details of processes seeming to hang up does vary. Sometimes ^C, ^T, and the like do not seem to work (or echo) at all. Top can stop updating for the likes of: # stress --hdd 12 --hdd-bytes 22G until ^C leads to stress exiting. Based on what top was reporting at the point its updates stopped, there still was lots of swap-space and no apparent need to have swapped out the kernel stacks for the top process. For example: 22% used. Another issue is that having systat -swap going as well leads to partial hang ups even for the likes of: # stress --hdd 8 --hdd-bytes 32G "Partial" in that some things stop but I've never had to force a reboot to get control: ^C for the stress run eventually works. I do not seem to have problems like any of the above for the likes of: # stress --hdd 1 --hdd-bytes 270G For this, "systat -swap" does progress the like of: Device/Path Size Used |0% /10 /20 /30 /40 / 60\ 70\ 80\ = 90\ 100| gpt/CA72opt0SWP 246G 154G XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX But not with the larger ---hdd figures above. I've not yet tried main [so: 14]. Note: These experiments are from attmpting to reproduce hangups seen during pourdiere-devel builds that have USE_TMPFS=3Dall and builders that are generating indefinitely growing log files. (This was actually under main targeting main .) =3D=3D=3D Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar)
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