From: Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Subject: Re: [PATCH 1/7] ext2: tell DAX the size of allocation holes
Date: Tue, 16 Aug 2016 16:52:27 -0600
Message-ID: <20160816225227.GA632@linux.intel.com>
References: <20160815190918.20672-1-ross.zwisler@linux.intel.com>
 <20160815190918.20672-2-ross.zwisler@linux.intel.com>
 <20160816091025.GA27284@quack2.suse.cz>
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Cc: Theodore Ts'o <tytso-3s7WtUTddSA@public.gmane.org>, linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org,
 Dave Chinner <david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
 linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Andreas Dilger <adilger.kernel-m1MBpc4rdrD3fQ9qLvQP4Q@public.gmane.org>,
 Alexander Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>, Jan Kara <jack-IBi9RG/b67k@public.gmane.org>,
 linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
 Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
To: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
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On Tue, Aug 16, 2016 at 11:10:25AM +0200, Jan Kara wrote:
> On Mon 15-08-16 13:09:12, Ross Zwisler wrote:
> > When DAX calls ext2_get_block() and the file offset points to a hole we
> > currently don't set bh_result->b_size.  When we re-enable PMD faults DAX
> > will need bh_result->b_size to tell it the size of the hole so it can
> > decide whether to fault in a 4 KiB zero page or a 2 MiB zero page.
> > 
> > For ext2 we always want DAX to use 4 KiB zero pages, so we just tell DAX
> > that all holes are 4 KiB in size.
> > 
> > Signed-off-by: Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
> > ---
> >  fs/ext2/inode.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> > index d5c7d09..c6d9763 100644
> > --- a/fs/ext2/inode.c
> > +++ b/fs/ext2/inode.c
> > @@ -773,6 +773,12 @@ int ext2_get_block(struct inode *inode, sector_t iblock, struct buffer_head *bh_
> >  	if (ret > 0) {
> >  		bh_result->b_size = (ret << inode->i_blkbits);
> >  		ret = 0;
> > +	} else if (ret == 0 && IS_DAX(inode)) {
> 
> I'd just drop the IS_DAX() check and set
> 
> 	bh_result->b_size = 1 << inode->i_blkbits;
> 
> IMO it's better to have things consistent between DAX & !DAX whenever
> possible.

Agreed, this is better.  Fixed for v2, thanks!