>>> vm.dirty_writeback_centisecs = 1500 >> which is used as an example to describe the bug in the following. >> >> After boot, >>> cat /proc/sys/vm/dirty_writeback_centisecs >> returns >> 500, > > Do you use any power management tools, like acpi-support, > laptop-mode-tools or pm-utils? If so, one of those might be setting that > value on ac/battery changes. acpi-support and laptop-mode-tools are not installed, but pm-utils is installed (version 1.4.1-14). A search through the results of > grep 500 $(dpkg -S pm-utils | sed 's/^.* //') does not give any plausible result
> I suspect laptop-mode-tools is the culprit: > > http://sources.debian.net/src/laptop-mode-tools/1.64-1/usr/share/laptop-mode > -tools/modules/laptop-mode?hl=418#L418 > > set_sysctl /proc/sys/vm/dirty_writeback_centisecs "$U_AGE" > > and > > usr/share/laptop-mode-tools/modules/laptop-mode: U_AGE=$((100*$DEF_UPDATE)) > usr/sbin/laptop_mode:DEF_UPDATE=5 > > → there you have your 500 Thanks for your investigation, but as mentioned: laptop-mode-tools is not installed. I guess the value dirty_writeback_centisecs defaults to 500. Other values defined via sysctl have their (suspected) default value, too, after boot and only change to the desired value after restarting the service manually as described. Thus, I guess that the sysctl service is not started correctly, although I cannot explain why systemctl should state otherwise (active, success) in this case.
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