linux-kernel - Re: block allocator issue with ext4+DAX

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Date:	Thu, 31 Mar 2016 09:13:58 -0600
From:	Ross Zwisler <ross.zwisler@...ux.intel.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: block allocator issue with ext4+DAX

On Thu, Mar 31, 2016 at 10:59:25AM +0200, Jan Kara wrote:
> On Wed 30-03-16 16:01:29, Ross Zwisler wrote:
> > I've hit an issue in my testing which I believe to be related to the ext4
> > block allocator when using the DAX mount option.  I originally found this
> > issue with the generic/102 xfstest, but have reduced it to the minimal
> > reproducer at the bottom of this email.  I've been able to reproduce this with
> > both BRD and with PMEM as the underlying block device.
> > 
> > For this test we're running in a very small filesystem, only 512 MiB.  We
> > fallocate() 400 MiB of that space, unlink the file, then try and rewrite that
> > 400 MiB file one chunk at a time.
> > 
> > What actually happens is that during the rewrite we run out of memory and the
> > DAX call to get_block() in dax_io() fails with -ENOSPC.
> 
> Yes, I have already sent a fix for this bug here:
> 
> http://www.spinics.net/lists/linux-ext4/msg51649.html
> 
> Ted, can you please pick it up? Thanks!
> 
> 								Honza

Yay!

Ted, you can add my

Tested-by: Ross Zwisler <ross.zwisler@...ux.intel.com>

to that patch.

Thanks for the fix, Jan!