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

[Casey McGinty]

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On Thu, May 28, 2009 at 9:43 PM, Bart Samwel <bart at samwel.tk> wrote:

> Hi Casey,
>
>
> The thing is, laptop mode does a sync *across all file systems*. And
> that causes disk activity even on file systems that aren't being used
> much. Combine this with a laptop mode sync loop (as you are
> experiencing) and it becomes very annoying. :-/


Well, that sounds like a fundamental flaw to me. I'm not sure why you would
want to cause a write on a file system that has no data to write.


I personally haven't verified this, so I will have to go and build such
> a set-up myself to reproduce the problem. I strongly suspect that LVM
> writes data after the sync is complete, which causes laptop mode to
> trigger a re-sync after two seconds.
>

This seems logical. A more likely scenario might be that the write is going
to update the timestamp or some flag on the RAID superblock to indicate that
the devices in the array are consistent. If this is true, then laptop-mode
is clearly broken for systems with RAID.

For now it looks like I've reached the limitations of "laptop-mode" on my
system. I'll check back in periodically to see how the progress is going.
Thanks for all the help and advice.

- Casey

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<br><br><div class=3D"gmail_quote">On Thu, May 28, 2009 at 9:43 PM, Bart Sa=
mwel <span dir=3D"ltr">&lt;<a href=3D"mailto:bart at samwel.tk">bart at samwel.tk=
</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" style=3D"border=
-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-lef=
t: 1ex;">
Hi Casey,<br><div class=3D"im"><br>
<br>
</div>The thing is, laptop mode does a sync *across all file systems*. And<=
br>
that causes disk activity even on file systems that aren&#39;t being used<b=
r>
much. Combine this with a laptop mode sync loop (as you are<br>
experiencing) and it becomes very annoying. :-/</blockquote><div class=3D"i=
m"><br>Well, that sounds like a fundamental flaw to me. I&#39;m not sure wh=
y you would want to cause a write on a file system that has no data to writ=
e.<br>
<br>
<br>
</div><blockquote class=3D"gmail_quote" style=3D"border-left: 1px solid rgb=
(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">I personall=
y haven&#39;t verified this, so I will have to go and build such<br>
a set-up myself to reproduce the problem. I strongly suspect that LVM<br>
writes data after the sync is complete, which causes laptop mode to<br>
trigger a re-sync after two seconds.<br>
</blockquote><div><br>This seems logical. A more likely scenario might be t=
hat the write is going to update the timestamp or some flag on the RAID sup=
erblock to indicate that the devices in the array are consistent. If this i=
s true, then laptop-mode is clearly broken for systems with RAID.<br>
<br>For now it looks like I&#39;ve reached the limitations of &quot;laptop-=
mode&quot; on my system. I&#39;ll check back in periodically to see how the=
 progress is going. Thanks for all the help and advice.<br><br>- Casey<br>
</div></div><br>

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