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    SubjectRe: [PATCHSET block#for-2.6.36-post] block: replace barrier with sequenced flush
    Hello,

    On 08/20/2010 03:22 PM, Christoph Hellwig wrote:
    > Many storage devices, especially in the consumer market, come with volatile
    > write back caches. That means the devices signal I/O completion to the
    > operating system before data actually has hit the physical medium.

    A bit nit picky but flash devices can also have writeback caches and
    the term physical medium sounds a bit off for those cases. Maybe just
    saying "non-volatile media" is better?

    > Implementation details for filesystems
    > --------------------------------------
    >
    > Filesystem can simply set the REQ_FLUSH and REQ_FUA bits and do not have to
    > worry if the underlying devices need any explicit cache flushing and how
    > the Forced Unit Access is implemented. The REQ_FLUSH and REQ_FUA flags
    > may both be set on a single bio.

    It may be worthwhile to explain the sequence of operations when
    REQ_FLUSH + data + REQ_FUA is executed. It can be extrapolated from
    the previous two descriptions but I think giving examples of different
    sequences depending on FLUSH/FUA configuration would be helpful to
    help understanding the overall picture of things.

    Other than those, looks good to me.

    Thanks.

    --
    tejun


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