pdflush in D state

[Patrick Mau <mau@oscar.ping.de>]

Hi there,

I have a strange observation regarding the pdflush kernel threads.
My system has 512MB RAM. The behavior is independand of the filesystem
type in use. I have tested ext2, ext3 and reiserfs.

The scenario goes like this:

- Create a new filesystem on a spare partition.
  All other partitions on this disk are NTFS and
  not mounted.
  
- Copy the whole XFree source there.

- "sync ; sync ; sync" and wait a few minutes
  (I really tried waiting more than 5 minutes)
  
- now there are 400MB used by the page cache

- start the build with "make World"

XFree creates its Makefiles using "imake".
After that it tries to remove many non-existant files to clean
the source tree.

This goes extremly fast, but after a few seconds pdflush
gets stuck in D state and tries to write back dirty pages.
The machine is completly unresponsive and "top" reports
75 percent IO wait time. The actual build has not even started.

I have no idea what pdflush is trying to do ...
The files are already written and there is no other disk
activity involved. I even tried single-user mode.

The kernel is BK current 2.5.59, the machine is a P4@2.4 GHz.

Has somebody else observed this ?

cheers,
Patrick