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    SubjectRe: regression in page writeback
    On Wed, 23 Sep 2009 10:01:04 +0800 Wu Fengguang <fengguang.wu@intel.com> wrote:

    > > If there's still outstanding dirty data for any of those queues, both
    > > wb_kupdate() and background_writeout() will take a teeny sleep and then
    > > will re-poll the queues.
    > >
    > > Did that logic get broken?
    >
    > No, but the "teeny sleep" is normally much smaller. When io queue is
    > not congested, every io completion event will wakeup the congestion
    > waiters. Also A's event could wake up B's waiters.
    >
    > __freed_request() always calls blk_clear_queue_congested() if under
    > congestion threshold which in turn wakes up congestion waiters:
    >
    > if (rl->count[sync] < queue_congestion_off_threshold(q))
    > blk_clear_queue_congested(q, sync);
    >

    Yes. Have any problems been demonstrated due to that?

    And what's _sufficiently_ wrong with that to justify adding potentially
    thousands of kernel threads? It was always a design objective to avoid
    doing that.



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