On Mon, Jun 19, 2017 at 02:33:41PM -0600, Jens Axboe wrote:

That doesn't work, in case it's cleared, or for checking whether it has
been set or not. Oh well, I added a NOT_SET variant for this. See below
for an incremental that adds support for file write hints as well. Use
the file write hint, if we have it, otherwise use the inode provided
one.

Setting hints on a file propagates to the inode, only if the inode doesn't
currently have a hint set.

Question:  IFF we can get the per-file hints to propagate to the
writeback code (which I think is pretty easy for ext4/xfs/bdev, not
sure about btrfs) do we even need the per-inode ones at all?