Re: [PATCH 4 of 7] Turn the DIO lock_type parameter into a flags field

[Chris Mason <chris.mason@oracle.com>]

On Thu, Nov 02, 2006 at 09:58:58AM +1100, David Chinner wrote:
[ ...]

Thanks for the review, I'll incorporate these suggestions into the next
patch set.

> > +
> > +	/*
> > +	 * the placeholder code does filemap_write_and_wait, so if we
> > +	 * aren't using placeholders we have to do it here
> > +	 */
> > +	if (!(dio->flags & DIO_PLACEHOLDERS) && end > offset) {
> > +		struct address_space *mapping = iocb->ki_filp->f_mapping;
> >  		retval = filemap_write_and_wait_range(mapping, offset, end - 1);
> >  		if (retval)
> >  			goto out;
> 
> So that means XFS will now do three cache flushes on write (one in
> xfs_write(), one in generic_file_direct_IO() and yet another here....

I removed the flush before starting the IO in generic_file_direct_IO
because that is now done by the placeholders.  When placeholders aren't
used, we need the flush to match the old behavior.

I added the flush in generic_file_direct_IO after calling the direct_IO
func because invalidate_page_range2 requires the data to be flushed
first.  Otherwise it fails to free a dirty page with dirty buffers and
spits out -EIO.  This only happens when mapping->nrpages > 0, so it
should be very low cost in the common case.

It's messy, I'll try to refactor things a bit to make it cleaner (same
goes for i_mutex drop/lock).

-chris