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    SubjectRe: [PATCH 3.16 106/217] sd: disable discard_zeroes_data for UNMAP
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    >>>>> "Rafael" == Rafael David Tinoco <rafael.tinoco@canonical.com> writes:

    Rafael> It seems that changing discard method from UNMAP to WRITE
    Rafael> SAME(16) without using NDOB bit (as first described in
    Rafael> sbc3r35b.pdf) can cause performance problems on big discards
    Rafael> (since data-out buffer will be checked for every WRITE SAME
    Rafael> command). I think this is happening after this commit, since
    Rafael> NDOB bit wasn't implemented with this change (afaik, iirc).

    We don't currently use NDOB since there is no VPD parameter to key off
    of. I am also not aware of any devices that actually support it.

    I am working on some patches that changes how we submit write same and
    unmap down the stack to make it easier for the target subsystem to
    provide zeroing guarantees. Those changes will clean some of this up but
    they are 4.8 material.

    --
    Martin K. Petersen Oracle Linux Engineering

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