Bart Samwel writes: > This is the defined behaviour for laptop_mode. Whenever a *physical* > READ takes place, this is taken to indicate that the disk is spun up at > that time. The laptop_mode functionality then takes that opportunity to > sync any dirty data to disk, two seconds (or whatever value you put in > /proc/sys/vm/laptop_mode) after the physical disk activity has ceased. > The rationale behind this is that you want to sync your stuff when the > disk is spun up, and then you want to hold back writing back stuff for a > very long while. And the only way it can detect that the disk is spun up > is when there is physical disk activity. > > This is exactly what happens in your case. The READ activity reported by > block_dump is *physical* read activity: some data was needed that was > not cached in memory. block_dump does not show you what data was > retrieved from the ext3 fs *without* having to access the disk, it only > shows actual physical disk I/O. Yep sounds good, but this happens even if there is no dirty data needing a sync back to disk. $ grep 'Dirty\|Write' /proc/meminfo Dirty: 0 kB Writeback: 0 kB WritebackTmp: 0 kB $ cat /some/uncached/file >/dev/null Jan 1 11:43:49 gw kernel: cat(6615): READ block 864408 on hda1 Jan 1 11:43:51 gw kernel: kjournald(760): WRITE block 2376 on hda1 Note, the reason I ask is this is a SSD so just because a physical read has taken place recently unneeded writes should be avoided. Turning laptop_mode to 0, but leaving other settings the same resolves the uneeded write: $ echo 0 > /proc/sys/vm/laptop_mode $ grep 'Dirty\|Write' /proc/meminfo Dirty: 0 kB Writeback: 0 kB WritebackTmp: 0 kB $ cat /some/other/uncached/file >/dev/null Jan 1 11:47:15 gw kernel: cat(6653): READ block 864258 on hda1 -- Dave -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
