linux-kernel - Re: [vm] writing to UDF DVD+RW (/dev/sr0) while under memory pressure: box ==> doorstop

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Message-Id: <20080106122954.d8f04c98.akpm@linux-foundation.org>
Date:	Sun, 6 Jan 2008 12:29:54 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mike Galbraith <efault@....de>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [vm] writing to UDF DVD+RW (/dev/sr0) while under memory
 pressure: box ==> doorstop

On Sun, 06 Jan 2008 19:01:10 +0100 Mike Galbraith <efault@....de> wrote:

> 
> On Sun, 2008-01-06 at 10:42 +0100, Mike Galbraith wrote:
> > FWIW, here's box having same seizure writing to /dev/pktcdvd/sr0.
> 
> Ugh, horrid device IO ==> horrid VM AFIKT.  I'll continue rummaging, but
> I wonder, am I doing something _so_ stupid as to warrant zero response?
> 

Copying linux-mm might have helped.  Bad time of year, too.

>From the traces it looks like all IO has stopped and everyone is waiting
(directly or indirectly) for certain IO completions.  Is that really true,
or is IO still dribbling along?

>From the kswapd0 trace it would appear that UDF is doing synchronous writes
(udf_update_inode->sync_dirty_buffer) which perhaps is making things
mightily slow.

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