[laptop-mode] Enabling Laptop Mode Activate Pdflush Every 3-4 Seconds

[Bart Samwel]

Ritesh Raj Sarraf wrote:
> On Tuesday 26 May 2009 15:24:27 Casey McGinty wrote:
>> I'm hoping someone has a solution to this issue. I have a set of RAID
>> arrays that are not part of my root file system. Normally they are
>> inactive. However, when I ENABLE laptop-mode on my system, the drives are
>> written to every couple of seconds by pdflush. I am on Ubuntu 9.04 on a
>> desktop system. Here is my laptop-mode.conf file:
> 
> Can you investigate to see which process is really triggering the write ?
> AFAIK, the default behavior on ext3 filesystems is to trigger a sync every 5 
> seconds.
> With laptop-mode enabled this increases. A sync will only be triggered if 
> there are enough dirty buffers to be written.

I'd like to see some block_dump info for this, I think. I've heard about
a case like this before, and wasn't able to reproduce it here. Just to
be sure:

- This is a software RAID array going through lvm?
- What file system is running on the RAID array?

To get block_dump stats, use the following procedure:

1. Enable laptop mode.

2. Stop syslogd. (This is important, or this will recurse and bring your
system down.)

3. "dmesg > dmesg_before.txt; echo 1 > /proc/sys/vm/block_dump ; sleep
60 ; echo 0 > /proc/sys/vm/block_dump ; dmesg > dmesg_after.txt"

4. Open dmesg_before.txt and dmesg_after.txt. Remove the lines from
dmesg_after.txt that are also in dmesg.before.txt.

5. Send us the contents of dmesg_after.txt.

Casey, could you do that for us? This will tell us more about what's
going on.

Cheers,
Bart