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I am using powertop to check that my machine is setup in a way that will give me good battery life. After installing laptop-mode-tools all of the "Tunables" section shows "Good" except VM writeback timeout. On the powertop page, it seems to suggest that 1500 (i.e. 15 seconds) is a good value. Checking cat /proc/sys/vm/dirty_writeback_centisecs shows that my current value is 60000 (i.e. 600 seconds or 10 minutes). I believe a larger value means to wait longer between writes (which means spinning up the drive less frequently). Do I really need to set the timeout longer than ten minutes?

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Just a note: you can configure those values in /etc/laptop-mode/laptop-mode.conf (LM_BATT_MAX_LOST_WORK_SECONDS). Personally i think 10 minutes is too much (i use 20 seconds). – Salem Sep 24 '12 at 21:40
You should also be able to put vm.dirty_writeback_centisecs=1500 in /etc/sysctl.d/99-vm-writeback.conf and reboot or do sudo service procps start – unhammer Mar 20 '14 at 7:04

The larger the dirty writeback setting the longer dirty pages sit in memory before being flushed out to disk. The downside is that this increases the window of opportunity for losing data if you lose power since there will be probably more dirty pages sitting in memory and not flushed out.

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