Re: How to find out, what "pdflush" is working on

[Chris Snook <csnook@redhat.com>]

Martin Knoblauch wrote:
> 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.

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

-- Chris