Hi,

 I find the following comment in mm/pdflush.c

/*
 * The pdflush threads are worker threads for writing back dirty data.
 * Ideally, we'd like one thread per active disk spindle.  But the disk
 * topology is very hard to divine at this level.   Instead, we take
 * care in various places to prevent more than one pdflush thread from
 * performing writeback against a single filesystem.  pdflush threads
 * have the PF_FLUSHER flag set in current->flags to aid in this.
 */

 Is there a way to find out what a certain instance of "pdflush" is working on? Like which block-device or which fliesystem it is writing to? I am still (2.6.27) trying to track down why writing a single file can make linux very sluggish and unresponsive. If that happens I usually see all possible 8 "pdflush" threads being in "D"-state. According to above comment only one of them should be really busy.

Cheers
Martin
------------------------------------------------------
Martin Knoblauch
email: k n o b i AT knobisoft DOT de
www:   http://www.knobisoft.de

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The key word is "ideally".  We'd like it to work that way, but it doesn't. 
Patches to fix this are welcome.

-- Chris
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Something based upon the following systemtap script may help:

probe kernel.function("__writeback_single_inode") {
  if (execname() == "pdflush")
     printf("pdflush %d writeback bdev %x inode %x\n", tid(), $inode->i_rdev, $inode->i_ino) 
}

Other fields are available as $inode->FOO.

- FChE
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