linux-ext4 - Re: Test ext4/001

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Date:	Thu, 22 Oct 2015 15:22:13 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org, fstests@...r.kernel.org
Subject: Re: Test ext4/001

On Thu, Oct 22, 2015 at 11:10:17AM +0200, Jan Kara wrote:
> 
> I've checked why test ext4/001 fails for me with DAX and after some
> investigation I've realized that the test assumes that
> extent_max_zeroout_kb is 32 KB and thus unwritten extent will get converted
> to written as a whole and not split. With DAX that doesn't happen (because
> of difference between EXT4_GET_BLOCKS_ flags passed in writeback path and
> DAX write path) and so the result differs.

Out of curiosity, how much memory are you using to test ext4 with DAX?
I assume you're doing something like what Matthew Wilcox documented
at: http://patchwork.ozlabs.org/patch/491107/

I should really figure out a way to automate doing DAX regression
testing using my scripts.

> So I was wondering how to best fix this. Either we could switch
> extent_max_zeroout_kb to 0 to make the result same (but that has a slight
> disadvantage that we would lose testing of the zeroout logic) or we could
> increase file size so that zeroout doesn't trigger or something else?
> Anyone has some idea?

The approach I would suggest is to fork 001.out to 001.out.zeroout and
001.out.nozerrout, and then test to see if our output file matches
either file.  That means we'll redirect the output to our own 001.tmp2
file and do the check against the two possible 001.out files in the
ext4/001 script, but the advantage of doing things that way is that is
that will also solve a false positive we're seeing when ext4
encryption is enabled, and for a similar reason (extent zero-out is
disabled when encryption is enabled).

Cheers,

						- Ted
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