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    SubjectRe: [PATCH 18/45] writeback: introduce wait queue for balance_dirty_pages()
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    On Thu, 2009-10-08 at 10:01 +0900, KAMEZAWA Hiroyuki wrote:

    > May I ask a question ? (maybe not directly related to this patch itself, sorry)
    >
    > Recent works as "writeback: switch to per-bdi threads for flushing data"
    > removed congestion_wait() from balance_dirty_pages() and added
    > schedule_timeout_interruptible().
    >
    > And this one replaces it with wake_up+wait_queue.
    >
    > IIUC, "iowait" cpustat data was calculated by runqueue->nr_iowait as
    > == kernel/schec.c
    > void account_idle_time(cputime_t cputime)
    > {
    > struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
    > cputime64_t cputime64 = cputime_to_cputime64(cputime);
    > struct rq *rq = this_rq();
    >
    > if (atomic_read(&rq->nr_iowait) > 0)
    > cpustat->iowait = cputime64_add(cpustat->iowait, cputime64);
    > else
    > cpustat->idle = cputime64_add(cpustat->idle, cputime64);
    > }
    > ==
    > Then, for showing "cpu is in iowait", runqueue->nr_iowait should be modified
    > at some places. In old kernel, congestion_wait() at el did that by calling
    > io_schedule_timeout().
    >
    > How this runqueue->nr_iowait is handled now ?

    Ah, I think you've got a good point, we need a io_schedule() there.





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