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    SubjectRe: Processes stuck on D state on Dual Opteron
    Nick Piggin wrote:
    > Nick Piggin wrote:
    >
    >> Chen, Kenneth W wrote:
    >
    >
    >>> I like the patch a lot and already did bench it on our db setup.
    >>> However,
    >>> I'm seeing a negative regression compare to a very very crappy patch
    >>> (see
    >>> attached, you can laugh at me for doing things like that :-).
    >>>
    >>
    >> OK - if we go that way, perhaps the following patch may be the
    >> way to do it.
    >>
    >
    > Here.
    >

    Actually yes this is good I think.

    What I was worried about is that you could lose some fairness due
    to not being put on the queue before allocation.

    This is probably a silly thing to worry about, because up until
    that point things aren't really deterministic anyway (and before this
    patchset it would try doing a GFP_ATOMIC allocation first anyway).

    However after the subsequent locking rework, both these get_request()
    calls will be performed under the same lock - giving you the same
    fairness. So it is nothing to worry about anyway!

    It is a bit subtle: get_request may only drop the lock and return NULL
    (after retaking the lock), if we fail on a memory allocation. If we
    just fail due to unavailable queue slots, then the lock is never
    dropped. And the mem allocation can't fail because it is a mempool
    alloc with GFP_NOIO.

    Nick

    --
    SUSE Labs, Novell Inc.


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