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From: Jon Nelson <jnelson@jamponi.net>
Date: Sun, 12 Dec 2010 07:11:28 -0600
Message-ID: <AANLkTikZkCs7Wee2=uhe3bw96Pggcv0jsCkZ+nkWEQ+=@mail.gmail.com>
Subject: Re: hunt for 2.6.37 dm-crypt+ext4 corruption? (was: Re: dm-crypt
 barrier support is effective)
To: "Ted Ts'o" <tytso@mit.edu>, Jon Nelson <jnelson@jamponi.net>,
        Matt <jackdachef@gmail.com>, Chris Mason <chris.mason@oracle.com>,
        Andi Kleen <andi@firstfloor.org>, Mike Snitzer <snitzer@redhat.com>,
        Milan Broz <mbroz@redhat.com>,
        linux-btrfs <linux-btrfs@vger.kernel.org>,
        dm-devel <dm-devel@redhat.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        htd <htd@fancy-poultry.org>, htejun <htejun@gmail.com>,
        linux-ext4 <linux-ext4@vger.kernel.org>
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On Sun, Dec 12, 2010 at 6:43 AM, Ted Ts'o <tytso@mit.edu> wrote:
> On Sun, Dec 12, 2010 at 04:18:29AM -0600, Jon Nelson wrote:
>> > I have one CPU configured in the environment, 512MB of memory.
>> > I have not done any memory-constriction tests whatsoever.
>
> I've finally been able to reproduce it myself, on real hardware.  SMP
> is not necessary to reproduce it, although having more than one CPU
> doesn't hurt.  What I did need to do (on real hardware with 4 gigs of
> memory) was to turn off swap and pin enough memory so that free memory
> was around 200megs or so before the start of the test.  (This is the
> natural amount of free memory that the system would try to reach,
> since 200 megs is about 5% of 4 gigs.)
>
> Then, during the test, free memory would drop to 50-70 megabytes,
> forcing writeback to run, and then I could trigger it about 1-2 times
> out of three.
>
> I'm guessing that when you used 512mb of memory, that was in effect a
> memory-constriction test, and if you were to push the memory down a
> little further, it might reproduce even more quickly.  My next step is
> to try to reproduce this in a VM, and then I can start probing to see
> what might be going on.

I'm glad you've been able to reproduce the problem! If you should need
any further assistance, please do not hesitate to ask.


-- 
Jon