What should VM writeback timeout be set to for a laptop?

Question

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?

Answer 1

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.