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kern/56309: swapctl -U is very inefficient (tages ages to eternities)
>Synopsis: swapctl -U is very inefficient (tages ages to eternities)
>Arrival-Date: Wed Jul 14 08:15:00 +0000 2021
>Originator: Frank Kardel
>Release: NetBSD 9.99.80 (also - .85 and likely beyond)
System: NetBSD pip 9.99.80 NetBSD 9.99.80 (PIPGEN) #0: Thu Feb 11 20:11:26 CET 2021 kardel@pip:/src/NetBSD/cur/src/obj.amd64/sys/arch/amd64/compile/PIPGEN amd64
On a system with swap configured and swap having been used shutdown can
take a very long time when shutting down in the "Removing block-type swap devices"
phase. The read rate from the swap devices is very low for rust media and slow
for SSD media. swapctl -U picks up significant CPU time. The whole process takes
eternities for rust media and ages for SSDs.
Example (about 7 minutes into the shutdown):
0 12876 23709 25309 117 -20 19376 1656 - O< ? 6:18.30 swapctl -U -t blk
0 188 22490 84 117 0 17820 1400 tstile D+ pts/2 0:00.00 swapctl -l
On rust media the shutdown can take several hours. Even SSDs(NVME) can take several
tens of minutes.
Use a system with swap enabled. Force the system to use swap space. Watch
a very long shutdown.
Workaround: set swapoff=NO in /etc/rc.conf.
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