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    Subject[PATCH 32/51] writeback: implement backing_dev_info->tot_write_bandwidth
    Date
    cgroup writeback support needs to keep track of the sum of
    avg_write_bandwidth of all wb's (bdi_writeback's) with dirty inodes to
    distribute write workload. This patch adds bdi->tot_write_bandwidth
    and updates inode_wb_list_move_locked(), inode_wb_list_del_locked()
    and wb_update_write_bandwidth() to adjust it as wb's gain and lose
    dirty inodes and its avg_write_bandwidth gets updated.

    As the update events are not synchronized with each other,
    bdi->tot_write_bandwidth is an atomic_long_t.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    Cc: Jens Axboe <axboe@kernel.dk>
    Cc: Jan Kara <jack@suse.cz>
    ---
    fs/fs-writeback.c | 7 ++++++-
    include/linux/backing-dev-defs.h | 2 ++
    mm/page-writeback.c | 3 +++
    3 files changed, 11 insertions(+), 1 deletion(-)

    diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
    index 0a90dc55..bbccf68 100644
    --- a/fs/fs-writeback.c
    +++ b/fs/fs-writeback.c
    @@ -99,6 +99,8 @@ static bool wb_io_lists_populated(struct bdi_writeback *wb)
    return false;
    } else {
    set_bit(WB_has_dirty_io, &wb->state);
    + atomic_long_add(wb->avg_write_bandwidth,
    + &wb->bdi->tot_write_bandwidth);
    return true;
    }
    }
    @@ -106,8 +108,11 @@ static bool wb_io_lists_populated(struct bdi_writeback *wb)
    static void wb_io_lists_depopulated(struct bdi_writeback *wb)
    {
    if (wb_has_dirty_io(wb) && list_empty(&wb->b_dirty) &&
    - list_empty(&wb->b_io) && list_empty(&wb->b_more_io))
    + list_empty(&wb->b_io) && list_empty(&wb->b_more_io)) {
    clear_bit(WB_has_dirty_io, &wb->state);
    + atomic_long_sub(wb->avg_write_bandwidth,
    + &wb->bdi->tot_write_bandwidth);
    + }
    }

    /**
    diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
    index 7a94b78..d631a61 100644
    --- a/include/linux/backing-dev-defs.h
    +++ b/include/linux/backing-dev-defs.h
    @@ -142,6 +142,8 @@ struct backing_dev_info {
    unsigned int min_ratio;
    unsigned int max_ratio, max_prop_frac;

    + atomic_long_t tot_write_bandwidth; /* sum of active avg_write_bw */
    +
    struct bdi_writeback wb; /* the root writeback info for this bdi */
    struct bdi_writeback_congested wb_congested; /* its congested state */
    #ifdef CONFIG_CGROUP_WRITEBACK
    diff --git a/mm/page-writeback.c b/mm/page-writeback.c
    index e31dea9..c95eb24 100644
    --- a/mm/page-writeback.c
    +++ b/mm/page-writeback.c
    @@ -881,6 +881,9 @@ static void wb_update_write_bandwidth(struct bdi_writeback *wb,
    avg += (old - avg) >> 3;

    out:
    + if (wb_has_dirty_io(wb))
    + atomic_long_add(avg - wb->avg_write_bandwidth,
    + &wb->bdi->tot_write_bandwidth);
    wb->write_bandwidth = bw;
    wb->avg_write_bandwidth = avg;
    }
    --
    2.4.0


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