On Mon, May 2, 2016 at 8:41 AM, Boaz Harrosh [off-list ref] wrote:

On 04/29/2016 12:16 AM, Vishal Verma wrote:

quoted

All IO in a dax filesystem used to go through dax_do_io, which cannot
handle media errors, and thus cannot provide a recovery path that can
send a write through the driver to clear errors.

Add a new iocb flag for DAX, and set it only for DAX mounts. In the IO
path for DAX filesystems, use the same direct_IO path for both DAX and
direct_io iocbs, but use the flags to identify when we are in O_DIRECT
mode vs non O_DIRECT with DAX, and for O_DIRECT, use the conventional
direct_IO path instead of DAX.

Really? What are your thinking here?

What about all the current users of O_DIRECT, you have just made them
4 times slower and "less concurrent*" then "buffred io" users. Since
direct_IO path will queue an IO request and all.
(And if it is not so slow then why do we need dax_do_io at all? [Rhetorical])

I hate it that you overload the semantics of a known and expected
O_DIRECT flag, for special pmem quirks. This is an incompatible
and unrelated overload of the semantics of O_DIRECT.

I think it is the opposite situation, it us undoing the premature
overloading of O_DIRECT that went in without performance numbers.
This implementation clarifies that dax_do_io() handles the lack of a
page cache for buffered I/O and O_DIRECT behaves as it nominally would
by sending an I/O to the driver.  It has the benefit of matching the
error semantics of a typical block device where a buffered write could
hit an error filling the page cache, but an O_DIRECT write potentially
triggers the drive to remap the block.