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    SubjectRe: [PATCH] umem: fix up unplugging.
    On Thu, Apr 5, 2012 at 4:51 PM, Jens Axboe <axboe@kernel.dk> wrote:
    > On 2012-04-04 17:58, Tao Guo wrote:
    >> On Wed, Apr 4, 2012 at 4:18 PM, Jens Axboe <axboe@kernel.dk> wrote:
    >>> On 2012-04-04 16:20, Tao Guo wrote:
    >>>> Hi Andrew,
    >>>>
    >>>> Thanks for your reply.
    >>>>
    >>>> Yes, without this patch the umem driver just doesn't work.
    >>>> It is a bug introduced by commit 7eaceaccab5f40bbfda044629a6298616aeaed50.
    >>>> In that patch, Jens removed the whole mm_unplug_device() function,
    >>>> which used to be
    >>>> the trigger to make umem start to work.
    >>>
    >>> Hmm indeed, that's isn't terribly useful. Why aren't we just calling
    >>> activate_card() on addition of a bio?
    >>>
    >> It is the original design idea, the umem driver also wants to do batch
    >> IO the same as
    >> hard disk drive to fully utilize the IO bandwidth.
    >
    > Sure, just wondering whether the benefits have been tested. But yes, it
    > certainly makes sense.
    >
    > Your patch looks buggy, though. What if the card is currently plugged on
    > another tasks plug list? You seem to assume that it can only be plugged
    > once.
    No, it will register in its own plug callback list successfully, so
    the unplug functions
    will be called separately(twice the same).
    -Tao
    >
    > --
    > Jens Axboe
    >


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