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    SubjectRe: 2.6.4-mm2
    Date
    In article <20040318235200.25c376a9.akpm@osdl.org> you write:
    >Jens Axboe <axboe@suse.de> wrote:
    >> I thought about this last night, and I have a better idea that gets the
    >> same accomplished. The problem right now is indeed that we aren't
    >> tracking who needs to be unplugged, like we used to. The solution is to
    >> do the exact same style plugging (with block helpers) that we used to,
    >> except the plug_list is maintained in the driver. So when you do
    >> dm_unplug(), it doesn't _have_ to iterate the full device list, only
    >> those that do need kicking.
    >
    >Yes, it would be nice but I fear that it gets complicated.
    >
    >Is it not the case that two dm maps can refer to the same queue? Say, one
    >map uses /dev/hda1 and another map uses /dev/hda2?
    >
    >If so, then when the /dev/hda queue is plugged we need to tell both the
    >higher-level maps that this queue needs an unplug. So blk_plug_device()
    >and the various unplug functions need to perform upcalls to an arbitrary
    >number of higher-level drivers, and those drivers need to keep track of the
    >currently-plugged queues without adding data structures to the
    >request_queue structure.
    >
    >It can be done of course, but could get messy.

    I implemented exactly this for the congestion stuff. It
    isn't perfect, but perhaps it is of some use:

    https://www.redhat.com/archives/linux-lvm/2004-February/msg00215.html

    It got shot down because it was too complicated..

    Mike.
    --
    Netu, v qba'g yvxr gur cynvagrkg :)
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