Bart Samwel writes: > This looks like it's a generic property of syncing an ext3 file system. > Try turning off laptop_mode and then running "sync". You will probably > see the same behaviour. yep, every sync() causes a gratuitous write to disk N seconds later even when no data has been read or written since the last sync(). $ while sleep 5; do sync; done ^C $ Jan 1 14:09:31 gw kernel: kjournald(760): WRITE block 2662 on hda1 Jan 1 14:09:36 gw kernel: kjournald(760): WRITE block 2664 on hda1 Jan 1 14:09:42 gw kernel: kjournald(760): WRITE block 2666 on hda1 Jan 1 14:09:47 gw kernel: kjournald(760): WRITE block 2668 on hda1 Jan 1 14:09:52 gw kernel: kjournald(760): WRITE block 2670 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: > > For your SSD I guess you need to get rid of the > sync-after-disk-activity, but keep the other VM behaviours of > laptop_mode (such as avoiding swapping out pages / writing back dirty > pages in order to free memory as long as it is also possible to just > drop pages that are not dirty). > > You can probably achieve this by: > - having a large commit interval etc., like you have now > - setting laptop_mode to a very large value, e.g. a couple of hours. > That will trigger a sync if and only if there has been *no* disk > activity at all for hours on end -- i.e., pretty much never. And the > other write-reducing VM features of laptop_mode will still be enabled. > > It would perhaps be a good thing to split these mechanisms into separate > knobs. Write batching (the sync-after-disk-activity stuff and also the > dirty_ratio / dirty_background_ratio changes) are a completely separate > mechanism from write avoidance (the other mechanism I mentioned). I'm going to run without laptop mode for a while to see how this goes. This system is a small router/firewall with most writes going to a tmpfs so the number of writes to the ext3 fs is only a few a month (provided no one logs into the system to do a config change). Thanks for the help. -- 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
