lkml.org 
[lkml]   [2011]   [Apr]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[PATCH 04/12] writeback: smoothed global/bdi dirty pages
    Maintain a smoothed version of dirty pages for use in the throttle
    bandwidth calculations.

    default_backing_dev_info.avg_dirty holds the smoothed global dirty
    pages.

    The calculation favors smoothness rather than accuracy. It's non-sense
    trying to track a much fluctuated value "accurately". And its users
    don't really rely on it being accurate.

    CC: larry <lantianyu1986@gmail.com>
    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    ---
    include/linux/backing-dev.h | 2 +
    mm/backing-dev.c | 3 +
    mm/page-writeback.c | 66 ++++++++++++++++++++++++++++++++++
    3 files changed, 71 insertions(+)

    --- linux-next.orig/mm/page-writeback.c 2011-04-13 17:18:12.000000000 +0800
    +++ linux-next/mm/page-writeback.c 2011-04-13 17:18:12.000000000 +0800
    @@ -471,6 +471,64 @@ unsigned long bdi_dirty_limit(struct bac
    return bdi_dirty;
    }

    +static void bdi_update_dirty_smooth(struct backing_dev_info *bdi,
    + unsigned long dirty)
    +{
    + unsigned long avg = bdi->avg_dirty;
    + unsigned long old = bdi->old_dirty;
    +
    + if (unlikely(!avg)) {
    + avg = dirty;
    + goto update;
    + }
    +
    + /*
    + * dirty pages are departing upwards, follow up
    + */
    + if (avg < old && old <= dirty) {
    + avg += (old - avg) >> 2;
    + goto update;
    + }
    +
    + /*
    + * dirty pages are departing downwards, follow down
    + */
    + if (avg > old && old >= dirty) {
    + avg -= (avg - old) >> 2;
    + goto update;
    + }
    +
    + /*
    + * This can filter out one half unnecessary updates when bdi_dirty is
    + * fluctuating around the balance point, and is most effective on XFS,
    + * whose pattern is
    + * .
    + * [.] dirty [-] avg . .
    + * . .
    + * . . . . . .
    + * --------------------------------------- . .
    + * . . . . . .
    + * . . . . . .
    + * . . . . . .
    + * . . . . . .
    + * . . . .
    + * . . . . (fluctuated)
    + * . . . .
    + * . . . .
    + *
    + * @avg will remain flat at the cost of being biased towards high. In
    + * practice the error tend to be much smaller: thanks to more coarse
    + * grained fluctuations, @avg becomes the real average number for the
    + * last two rising lines of @dirty.
    + */
    + goto out;
    +
    +update:
    + bdi->avg_dirty = avg;
    +out:
    + bdi->old_dirty = dirty;
    +}
    +
    static void __bdi_update_write_bandwidth(struct backing_dev_info *bdi,
    unsigned long elapsed,
    unsigned long written)
    @@ -535,6 +593,14 @@ void bdi_update_bandwidth(struct backing
    if (elapsed <= HZ / 5)
    goto unlock;

    + if (thresh &&
    + now - default_backing_dev_info.bw_time_stamp >= HZ / 5) {
    + bdi_update_dirty_smooth(&default_backing_dev_info, dirty);
    + default_backing_dev_info.bw_time_stamp = now;
    + }
    + if (thresh) {
    + bdi_update_dirty_smooth(bdi, bdi_dirty);
    + }
    __bdi_update_write_bandwidth(bdi, elapsed, written);

    snapshot:
    --- linux-next.orig/include/linux/backing-dev.h 2011-04-13 17:18:12.000000000 +0800
    +++ linux-next/include/linux/backing-dev.h 2011-04-13 17:18:12.000000000 +0800
    @@ -77,6 +77,8 @@ struct backing_dev_info {
    unsigned long written_stamp;
    unsigned long write_bandwidth;
    unsigned long avg_write_bandwidth;
    + unsigned long avg_dirty;
    + unsigned long old_dirty;

    struct prop_local_percpu completions;
    int dirty_exceeded;
    --- linux-next.orig/mm/backing-dev.c 2011-04-13 17:18:12.000000000 +0800
    +++ linux-next/mm/backing-dev.c 2011-04-13 17:18:12.000000000 +0800
    @@ -669,6 +669,9 @@ int bdi_init(struct backing_dev_info *bd
    bdi->write_bandwidth = INIT_BW;
    bdi->avg_write_bandwidth = INIT_BW;

    + bdi->avg_dirty = 0;
    + bdi->old_dirty = 0;
    +
    err = prop_local_init_percpu(&bdi->completions);

    if (err) {



    \
     
     \ /
      Last update: 2011-04-16 16:09    [W:0.029 / U:0.816 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site