On Sat, Mar 05, 2022 at 09:12:55AM +1100, Dave Chinner wrote:

AFAICT, all the filesystem/IO path passthrough plumbing for hints is
now gone, and no hardware will ever receive hints.  Doesn't this
mean that file_write_hint(), file->f_write_hint and iocb->ki_hint
are now completely unused, too?

No, for the reason tha you state below.  f2fs still uses it.

AFAICT, this patch leaves just the f2fs allocator usage of
inode->i_rw_hint to select a segment to allocate from as the
remaining consumer of this entire plumbing and user API. Is that
used by applications anywhere, or can that be removed and so the
rest of the infrastructure get removed and the fcntl()s no-op'd or
-EOPNOTSUPP?

I was told it is used quite heavily in android.