On 13:31 10/06, Qu Wenruo wrote:
> 
> 
> On 2020/6/6 上午4:48, Goldwyn Rodrigues wrote:
> > In current scenarios, for XFS, it would mean that a page invalidation
> > would end up being a writeback error. So, if iomap returns zero, fall
> > back to biffered I/O. XFS has never supported fallback to buffered I/O.
> > I hope it is not "never will" ;)
> > 
> > With mixed buffered and direct writes in btrfs, the pages may not be
> > released the extent may be locked in the ordered extents cleanup thread,
> 
> I'm wondering can we handle this case in a different way.
> 
> In fact btrfs has its own special handling for invalidating pages.
> Btrfs will first look for any ordered extents covering the page, finish
> the ordered extent manually, then invalidate the page.
> 
> I'm not sure why invalidate_inode_pages2_range() used in dio iomap code
> does not use the fs specific invalidatepage(), but only do_lander_page()
> then releasepage().
> 
> Shouldn'y we btrfs implement the lander_page() to handle ordered extents
> properly?
> Or is there any special requirement?
> 

The problem is aops->launder_page() is called only if PG_Dirty is
set. In this case it is not because we just performed a writeback.

Also, it is not just ordered ordered extent writeback which may lock
the extent, a buffered read can lock as well.

-- 
Goldwyn