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    SubjectRe: [PATCH 4/8] Use prepare_to_wait_exclusive() instead prepare_to_wait()
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    On Tue, 2009-12-15 at 09:58 -0500, Rik van Riel wrote:
    > On 12/15/2009 12:32 AM, Mike Galbraith wrote:
    > > On Tue, 2009-12-15 at 09:45 +0900, KOSAKI Motohiro wrote:
    > >>> On 12/14/2009 07:30 AM, KOSAKI Motohiro wrote:
    > >>>> if we don't use exclusive queue, wake_up() function wake _all_ waited
    > >>>> task. This is simply cpu wasting.
    > >>>>
    > >>>> Signed-off-by: KOSAKI Motohiro<kosaki.motohiro@jp.fujitsu.com>
    > >>>
    > >>>> if (zone_watermark_ok(zone, sc->order, low_wmark_pages(zone),
    > >>>> 0, 0)) {
    > >>>> - wake_up(wq);
    > >>>> + wake_up_all(wq);
    > >>>> finish_wait(wq,&wait);
    > >>>> sc->nr_reclaimed += sc->nr_to_reclaim;
    > >>>> return -ERESTARTSYS;
    > >>>
    > >>> I believe we want to wake the processes up one at a time
    > >>> here.
    >
    > >> Actually, wake_up() and wake_up_all() aren't different so much.
    > >> Although we use wake_up(), the task wake up next task before
    > >> try to alloate memory. then, it's similar to wake_up_all().
    >
    > That is a good point. Maybe processes need to wait a little
    > in this if() condition, before the wake_up(). That would give
    > the previous process a chance to allocate memory and we can
    > avoid waking up too many processes.

    Pondering, I think I'd at least wake NR_CPUS. If there's not enough to
    go round, oh darn, but if there is, you have full utilization quicker.

    $.02.

    -Mike



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