linux-ext4 - Re: A warning from 3.6+ with bigalloc and delalloc when running xfstest

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Date:	Thu, 11 Oct 2012 23:57:08 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Andrey Sidorov <qrxd43@...orola.com>
Cc:	Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: A warning from 3.6+ with bigalloc and delalloc when running
 xfstest

On Wed, Oct 10, 2012 at 01:02:52PM -0400, Andrey Sidorov wrote:
> On Tue, Oct 9, 2012 at 9:51 AM, Theodore Ts'o <tytso@....edu> wrote:
> 
> > It is indeed, something we need to fix, and it's part of the problem
> > where where the delayed allocation for bigalloc is completely screwed
> > up.  Part of the problem is when we write into a cluster which has not
> > yet been mapped in the extent tree, but which might (or might not)
> > have had other blocks in the cluster that have already been subject to
> > delayed allocation, we don't know whether to reserve clusters for the
> > purposes of doing the the delayed allocation accounting.  Fixing this
> > w/o the extent status tree means having to search the page cache and
> > for other pages in the cluster, which is not only painful, but tricky
> > from the perspective of lock ordering.
> >
> > Unfortunately, I didn't notice this problem originally because I
> > hadn't been doing regular xfstests runs with bigalloc, and most of my
> > testing had been with direct I/O, where these issues didn't come up.
> >
> >                                 - Ted
> 
> Hi Ted,
> 
> Does it mean I'd better turn off delalloc if I use bigalloc with linux 3.5.3?

Hi Andrey,

This warning is only triggered in a stress test case.  In our product
system we never meet this warning, certainly we have backported bigalloc
to 2.6.32 kernel, though.  So IMHO we needn't turn off delalloc.

Regards,
Zheng
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