Re: [dm-crypt] system freezes when using swap that is encrypted

From: Arno Wagner <arno@wagner.name>
To: dm-crypt@saout.de
Subject: Re: [dm-crypt] system freezes when using swap that is encrypted
Date: Fri, 12 Nov 2010 17:51:36 +0100	[thread overview]
Message-ID: <20101112165136.GA23352@tansi.org> (raw)
In-Reply-To: <AANLkTi=KAJOjf6Ac+8xU55+nrx6W1OH_-K18+dvnEm_n@mail.gmail.com>

Id this is not a hard freeze, but only an extreme slowdown,
then it probably is one of the known issues with write-barrierss.
Fortunately, the kernel folks have finally stopped twiddeling 
their thumbs and have started to do something about it.

The problem arises when writing a lot of data to a slower
device (among other things). The slowdown by the encryption
can be enough to trigger the issue. Also, doing something
like a "cat /dev/zero > ttt" tyically causes these freezes
that can take minutes or longer.

2.6.36 is alrady significantly improved, but contains
only part of the intended changes. 2.6.37 is expected
to be still better. I would recomend to try with 
2.6.36 for the moment.

Arno

On Fri, Nov 12, 2010 at 08:17:48AM -0700, Nicolas Bock wrote:
> Hello list,
> 
> I am using 2 primary FAT partitions for swap that I encrypt with cryptsetup
> on boot with a random password from /dev/urandom. I noticed that once memory
> pressure is high enough for the pager to start swapping, the system freezes.
> It seems as if it's only the disk that freezes however, when I am logged
> into a virtual console I can still use the keyboard to switch between
> different consoles and the magic sysreq keys are working. I can ping the
> machine but that's about it. Anything that seems to involve disk access like
> logging in, Ctrl-C'ing the high memory job, switching to graphical console,
> etc, does not work. I have tried to increase kernel logging with 'dmesg -n8'
> but to no avail. I do not  see any error messages when this happens. I am
> using  a vanilla kernel, version 2.6.34.5. Any pointers as to what could
> this be caused by or how I could track this down are greatly appreciated.
> 
> nick

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-- 
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@wagner.name 
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