Jens Axboe <axboe@xxxxxxxxx> writes: > DONTCACHE I/O must have the completion punted to a workqueue, just like > what is done for unwritten extents, as the completion needs task context > to perform the invalidation of the folio(s). However, if writeback is > started off filemap_fdatawrite_range() off generic_sync() and it's an > overwrite, then the DONTCACHE marking gets lost as iomap_add_to_ioend() > don't look at the folio being added and no further state is passed down > to help it know that this is a dropbehind/DONTCACHE write. > > Check if the folio being added is marked as dropbehind, and set > IOMAP_IOEND_DONTCACHE if that is the case. Then XFS can factor this into > the decision making of completion context in xfs_submit_ioend(). > Additionally include this ioend flag in the NOMERGE flags, to avoid > mixing it with unrelated IO. > > This fixes extra page cache being instantiated when the write performed > is an overwrite, rather than newly instantiated blocks. > > Fixes: b2cd5ae693a3 ("iomap: make buffered writes work with RWF_DONTCACHE") > Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> > > --- > > Found this one while testing the unrelated issue of invalidation being a > bit broken before 6.15 release. We need this to ensure that overwrites > also prune correctly, just like unwritten extents currently do. I guess I did report this to you a while ago when I was adding support for uncahed buffered-io to xfs_io. But I never heard back from you :( https://lore.kernel.org/all/87h649trof.fsf@xxxxxxxxx/ No worries, good that we finally have this fixed. -ritesh