"dirty writeback" frequency to save power

[Francisco Borges]

Hello,

If I use powertop, it will often advise me to increase the dirty
writeback frequency in order to save power. I normally do that with:

echo 1500 >! /proc/sys/vm/dirty_writeback_centisecs

However, this is reset with every reboot. Does anyone knows how to
configure this value?

I couldn't find anything about it in the laptop-mode.conf man page.

thanks in advance for any help,
-- 
Francisco