Re: [PATCH v11 20/21] ext4: Add DAX functionality

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

----- Original Message -----
> From: "Matthew Wilcox" <willy@linux.intel.com>
> To: "Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>
> Cc: "Matthew Wilcox" <matthew.r.wilcox@intel.com>, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
> linux-kernel@vger.kernel.org, "Ross Zwisler" <ross.zwisler@linux.intel.com>
> Sent: Friday, October 17, 2014 12:16:24 AM
> Subject: Re: [PATCH v11 20/21] ext4: Add DAX functionality
> 
[...]
> On Thu, Oct 16, 2014 at 02:56:25PM +0200, Mathieu Desnoyers wrote:
> > > @@ -3572,6 +3579,11 @@ static int ext4_fill_super(struct super_block *sb,
> > > void *data, int silent)
> > >  				 "both data=journal and dioread_nolock");
> > >  			goto failed_mount;
> > >  		}
> > > +		if (test_opt(sb, DAX)) {
> > > +			ext4_msg(sb, KERN_ERR, "can't mount with "
> > > +				 "both data=journal and dax");
> > 
> > This limitation regarding ext4 and dax should be documented in dax
> > Documentation.
> 
> Maybe the ext4 documentation too?  It seems kind of obvious to me that if
> ypu're enabling in-place-updates that you can't journal the data you're
> updating (well ... you could implement undo-log journalling, I suppose,
> which would be quite a change for ext4)

Yes, we could document this limitation in general for all journalling FS within
DAX documentation, and then document it specifically per-FS in the FS
documentation.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com