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    SubjectRe: [RFC] Generalize prio_tree (1/3)
    Nick Piggin wrote:
    > ... but humor me, you _are_ ensuring the following doesn't get
    > reordered, say:
    > (write, sect 100), (barrier), (write, sect 200)

    Ah you found the case I didn't mention :-) Yes, that's handled
    somewhere else. When the ABISS elevator sees a barrier, it just
    pushes the current sort tree for non-reads (writes and weird
    stuff) to a FIFO list.

    So writes don't benefit that much from priorities. The good
    thing is that they also happen to need them less ;-)

    Hmm, I just see that power down (suspend and shutdown) sneaked out
    again. Well, easy enough to fix.

    > No comment on your prio tree generalization, sorry. Other than: it
    > seems to be unfortunately quite ugly.

    I know. Unfortunately, there doesn't seem to be a nice alternative
    that doesn't either require additional fields (e.g. in MM, only half
    of the key is not stored in the tree, the other half is calculated)
    or *very* busy callbacks.

    Of course, if Rajesh or the MM folks in general think that storing
    the whole key in the tree is fine, I wouldn't complain :-)

    > (eg. add the patch to the front
    > of your ABISS elevator if you submit it to 2.6 or -mm).

    Ah no, the ABISS elevator won't go into the kernel - it's just for
    experimenting. But Jens is planning to add the overlap handling to
    the block device layer. So the user is well on its way :-) It's just
    more convenient if we can do this one step at a time, particularly
    since prio_tree is a very general concept (much like lists or
    red-black trees) anyway.

    > But I don't have strong feelings on the matter. If Rajesh says its OK
    > to go ahead as is, that would be fine by me :)

    Cool. Thanks !

    - Werner

    / Werner Almesberger, Buenos Aires, Argentina /
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