----- Original Message ----

> From: Chris Snook
> To: Martin Knoblauch
> Cc: linux-kernel@vger.kernel.org; Peter zijlstra ; Fengguang Wu
> Sent: Tuesday, September 16, 2008 9:07:29 PM
> Subject: Re: How to find out, what "pdflush" is working on
> 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.

Now, I am pretty much aware that apparently things are not "ideal". Therefore my question. Because before doing patches, one has to analyze.


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