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    SubjectRe: [RFC PATCH-tip v4 02/10] locking/rwsem: Stop active read lock ASAP
    On Mon, Oct 10, 2016 at 05:07:45PM +1100, Dave Chinner wrote:
    > > > *However*, the DAX IO path locking in XFS has changed in 4.9-rc1 to
    > > > match the buffered IO single writer POSIX semantics - the test is a
    > > > bad test based on the fact it exercised a path that is under heavy
    > > > development and so can't be used as a regression test across
    > > > multiple kernels.
    > >
    > > That being said - I wonder if we should allow the shared lock on DAX
    > > files IFF the user is specifying O_DIRECT in the open mode..
    > It should do - if it doesn't then we screwed up the IO path
    > selection logic in XFS and we'll need to fix it.

    Depends on your defintion of "we". The DAX code has always abused the
    direct I/O path, and that abuse is ingrained in the VFS path in a way that
    we can't easily undo it in XFS, e.g. take a look at io_is_direct and
    iocb_flags in include/linux/fs.h, which ensure that DAX I/O will always
    appear as IOCB_DIRECT to the fs. It will take some time to untagle
    this, but it's on my todo list once the last file system (ext4)
    untangles the DAX and direct I/O path.

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      Last update: 2016-10-10 12:13    [W:19.466 / U:0.168 seconds]
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