linux-ext4 - Re: [PATCH 2/7] dax: Add sync argument to dax_iomap

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Date:   Fri, 28 Jul 2017 11:40:01 +0200
From:   Jan Kara <jack@...e.cz>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Andy Lutomirski <luto@...nel.org>, linux-nvdimm@...ts.01.org,
        linux-xfs@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
        Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH 2/7] dax: Add sync argument to dax_iomap_fault()

On Thu 27-07-17 16:06:37, Ross Zwisler wrote:
> On Thu, Jul 27, 2017 at 03:12:40PM +0200, Jan Kara wrote:
> > Add 'sync' argument to dax_iomap_fault(). It will be used to communicate
> > the fact that synchronous fault is requested.
> 
> I don't actually think you need to pass this 'sync' parameter around.  I think
> you can completely rely on IOMAP_F_NEEDSYNC being set in iomap.flags.  The DAX
> fault handlers can call ops->iomap_begin() and use that flag for all the
> tests and make it our once source of truth.
> 
> That flag also tells us that we are doing a write fault (from
> ext4_iomap_begin()):
> 
> 	if ((flags & IOMAP_FAULT) && (flags & IOMAP_WRITE) && IS_SYNC(inode) &&
> 	    !jbd2_transaction_committed(EXT4_SB(inode->i_sb)->s_journal,
> 					EXT4_I(inode)->i_datasync_tid))
> 		iomap->flags |= IOMAP_F_NEEDDSYNC;
> 
> So conditionals like this from dax_iomap_pte_fault():
> 
> 	force_ro = (vmf->flags & FAULT_FLAG_WRITE) && sync &&
> 			(iomap.flags & IOMAP_F_NEEDDSYNC);
> 
> can be simplified to:
> 
> 	force_ro = (iomap.flags & IOMAP_F_NEEDDSYNC);

Yeah, probably you're right. I'll look into changing this.

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR