On Wed, Jan 9, 2019 at 4:44 PM Dave Chinner [off-list ref] wrote:

I wouldn't look at ext4 as an example of a reliable, problem free
direct IO implementation because, historically speaking, it's been a
series of nasty hacks (*cough* mount -o dioread_nolock *cough*) and
been far worse than XFS from data integrity, performance and
reliability perspectives.

That's some big words from somebody who just admitted to much worse hacks.

Seriously. XFS is buggy in this regard, ext4 apparently isn't.

Thinking that it's better to just invalidate the cache  for direct IO
reads is all kinds of odd.

                Linus