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    SubjectRe: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling
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    On Fri, Nov 13, 2015 at 4:06 PM, Ross Zwisler
    <ross.zwisler@linux.intel.com> wrote:
    > Currently the PMEM driver doesn't accept REQ_FLUSH or REQ_FUA bios. These
    > are sent down via blkdev_issue_flush() in response to a fsync() or msync()
    > and are used by filesystems to order their metadata, among other things.
    >
    > When we get an msync() or fsync() it is the responsibility of the DAX code
    > to flush all dirty pages to media. The PMEM driver then just has issue a
    > wmb_pmem() in response to the REQ_FLUSH to ensure that before we return all
    > the flushed data has been durably stored on the media.
    >
    > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>

    Hmm, I'm not seeing why we need this patch. If the actual flushing of
    the cache is done by the core why does the driver need support
    REQ_FLUSH? Especially since it's just a couple instructions. REQ_FUA
    only makes sense if individual writes can bypass the "drive" cache,
    but no I/O submitted to the driver proper is ever cached we always
    flush it through to media.


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