[plug] R52 ThinkPad - pdflush on large disk operations

[Onno Benschop]

Yesterday I saw some really sick behaviour when I was splitting an 8.6Gb
file into smaller chunks so I could burn it to DVD. The command I was
running was:

    split -b600m latte.tar.bz2 latte.tar.part-

And the file latte.tar.bz2 is the 8.6Gb file.


The behaviour I saw was that cron was forking all over the place, the
machine getting slower and slower. At one stage I had 86 cron processes
running which couldn't be killed. (You should know that I have two cron
jobs that run each minute to log traffic and current active window -
part of my client billing process.)

The other set of processes running was a whole bunch of pdflush instances.

I killed off my split command and the machine started coming back to life.

Several hours later I tried the split again and within a minute a whole
lot of pdflush processes, killing the split removed the pdflush.

What I think is happening is that the cron jobs are trying to write to
disk, they get blocked and the pdflush is really what is blocking the
whole lot.

I did some playing with hdparm and noticed that according to it I was
using 16 bit I/O, so I tried talking to my drive like I normally would,
hdparm -i /dev/sda and it turns out that hdparm doesn't like talking to
my drive.


Some background:

When I installed Debian on my machine I had all manner of challenges
getting an existing workstation install to mount. After many google
hours I realised that I was expecting my drive to be called /dev/hda,
but my machine was expecting it to be /dev/sda. After changing my fstab
all started working normally.

I'm running a 2.6.11 kernel.



Actual questions:

What is really happening? What can I do to address this? What google
terms should I use? Has anyone else seen this type of behaviour?


Cheers,
-- 
Onno Benschop

Connected via Optus B3 at S34°45'36.5" - E139°00'08.7" (Mount Pleasant, SA)
--
()/)/)()        ..ASCII for Onno..
|>>?            ..EBCDIC for Onno..
--- -. -. ---   ..Morse for Onno..

Proudly supported by Skipper Trucks, Highway1, Concept AV, Sony Central, Dalcon
ITmaze   -   ABN: 56 178 057 063   -  ph: 04 1219 8888   -   onno at itmaze.com.au