Re: Review: Clear unwritten flag on during partial page truncation

[David Chinner <dgc@sgi.com>]

On Fri, Dec 22, 2006 at 01:21:42PM +0000, Christoph Hellwig wrote:
> On Thu, Dec 21, 2006 at 05:16:58PM +1100, Nathan Scott wrote:
> > On Wed, 2006-12-20 at 17:28 +1100, David Chinner wrote:
> > > Hence the solution is to clear the private buffer flags in
> > > xfs_vm_invalidatepage() so that when we extend the file the buffers
> > > on the page are all consistent.
> > > 
> > > Patch below. Comments?
> > 
> > Looks good Dave, nice sleuthing.
> > 
> > In hindsight, it'd have been really good to have gone for the real
> > BH_Unwritten flag upfront, and then being able to clear that inside
> > discard_buffer (like was done for BH_Delay)... if we did that, then
> > all this new code we're adding here (to just clear_buffer_unwritten,
> > ultimately) and also the complete hack in xfs_count_page_state could
> > be removed.  It still might be worth considering doing that, in case
> > there's other hard-to-hit-but-not-yet-uncovered bugs lurking along
> > the same lines.  But alot of effort, with the possibility of it not
> > being merged at all, as it touches code outside XFS.  D'oh.
> 
> Getting code into buffer.c to fix this properly should be no problem
> at all.  As usual we prefer to fix core code instead of working around
> it.  This would also fix the data loss issue after we write through mmap
> into an unwritten extent.

Ok, I'll work up a patch for it in the new year, Christoph.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group