Re: kjournald() with DIO

[Badari Pulavarty <pbadari@us.ibm.com>]

On Wed, 2005-09-14 at 15:02 -0700, Andrew Morton wrote:
> Mingming Cao <cmm@us.ibm.com> wrote:
> >
> > I proposed similar idea to Andrea in the bug report before.  Andrea
> > expressed this concern: with this(try_to_free_buffers() still fail to
> > drop the buffer because of this elevated-refcount by kjournald),
> > block_read_full_page will not re-read from disk the buffers the next
> > time a buffered-IO read from disk, after the direct-io has completed.
> > This is because the buffer is marked uptodate. How could we handle this?
> 
> Well.  Application A has written data x with direct-io.  Application B has,
> at a later time, written, dirtied (or even read) data y with buffered I/O.
> 
> So the contents of pagecache are in fact correct, but it is not known
> whether or not the data on disk is correct.
> 
> I guess one way of resolving it is to make invalidate_inode_pages2_range()
> provide a hard guarantee: call truncate_complete_page() instead of
> invalidate_complete_page().  We need to have a think about the implications
> of that.  For starters, if someone gets in at the right time and
> reinstantiates a pte against the page, we'll end up converting that into an
> anonymous page.

FWIW, I changed it to call truncate_complete_page() and the tests ran
fine overnight.

Thanks,
Badari