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    Subject[PATCH 002 of 4] md: Define ->congested_fn for raid1, raid10, and multipath

    raid1, raid10 and multipath don't report their 'congested' status
    through bdi_*_congested, but should.

    This patch adds the appropriate functions which just check the
    'congested' status of all active members (with appropriate locking).

    raid1 read_balance should be modified to prefer devices where
    bdi_read_congested returns false. Then we could use the '&' branch
    rather than the '|' branch. However that should would need
    some benchmarking first to make sure it is actually a good idea.

    Signed-off-by: Neil Brown <neilb@suse.de>

    ### Diffstat output
    ./drivers/md/multipath.c | 24 ++++++++++++++++++++++++
    ./drivers/md/raid1.c | 28 ++++++++++++++++++++++++++++
    ./drivers/md/raid10.c | 22 ++++++++++++++++++++++
    3 files changed, 74 insertions(+)

    diff .prev/drivers/md/multipath.c ./drivers/md/multipath.c
    --- .prev/drivers/md/multipath.c 2006-08-29 14:52:50.000000000 +1000
    +++ ./drivers/md/multipath.c 2006-08-29 14:33:34.000000000 +1000
    @@ -228,6 +228,28 @@ static int multipath_issue_flush(request
    rcu_read_unlock();
    return ret;
    }
    +static int multipath_congested(void *data, int bits)
    +{
    + mddev_t *mddev = data;
    + multipath_conf_t *conf = mddev_to_conf(mddev);
    + int i, ret = 0;
    +
    + rcu_read_lock();
    + for (i = 0; i < mddev->raid_disks ; i++) {
    + mdk_rdev_t *rdev = rcu_dereference(conf->multipaths[i].rdev);
    + if (rdev && !test_bit(Faulty, &rdev->flags)) {
    + request_queue_t *q = bdev_get_queue(rdev->bdev);
    +
    + ret |= bdi_congested(&q->backing_dev_info, bits);
    + /* Just like multipath_map, we just check the
    + * first available device
    + */
    + break;
    + }
    + }
    + rcu_read_unlock();
    + return ret;
    +}

    /*
    * Careful, this can execute in IRQ contexts as well!
    @@ -509,6 +531,8 @@ static int multipath_run (mddev_t *mddev

    mddev->queue->unplug_fn = multipath_unplug;
    mddev->queue->issue_flush_fn = multipath_issue_flush;
    + mddev->queue->backing_dev_info.congested_fn = multipath_congested;
    + mddev->queue->backing_dev_info.congested_data = mddev;

    return 0;

    diff .prev/drivers/md/raid1.c ./drivers/md/raid1.c
    --- .prev/drivers/md/raid1.c 2006-08-29 14:52:50.000000000 +1000
    +++ ./drivers/md/raid1.c 2006-08-29 14:26:59.000000000 +1000
    @@ -601,6 +601,32 @@ static int raid1_issue_flush(request_que
    return ret;
    }

    +static int raid1_congested(void *data, int bits)
    +{
    + mddev_t *mddev = data;
    + conf_t *conf = mddev_to_conf(mddev);
    + int i, ret = 0;
    +
    + rcu_read_lock();
    + for (i = 0; i < mddev->raid_disks; i++) {
    + mdk_rdev_t *rdev = rcu_dereference(conf->mirrors[i].rdev);
    + if (rdev && !test_bit(Faulty, &rdev->flags)) {
    + request_queue_t *q = bdev_get_queue(rdev->bdev);
    +
    + /* Note the '|| 1' - when read_balance prefers
    + * non-congested targets, it can be removed
    + */
    + if ((bits & (1<<BDI_write_congested)) || 1)
    + ret |= bdi_congested(&q->backing_dev_info, bits);
    + else
    + ret &= bdi_congested(&q->backing_dev_info, bits);
    + }
    + }
    + rcu_read_unlock();
    + return ret;
    +}
    +
    +
    /* Barriers....
    * Sometimes we need to suspend IO while we do something else,
    * either some resync/recovery, or reconfigure the array.
    @@ -1965,6 +1991,8 @@ static int run(mddev_t *mddev)

    mddev->queue->unplug_fn = raid1_unplug;
    mddev->queue->issue_flush_fn = raid1_issue_flush;
    + mddev->queue->backing_dev_info.congested_fn = raid1_congested;
    + mddev->queue->backing_dev_info.congested_data = mddev;

    return 0;

    diff .prev/drivers/md/raid10.c ./drivers/md/raid10.c
    --- .prev/drivers/md/raid10.c 2006-08-29 14:50:34.000000000 +1000
    +++ ./drivers/md/raid10.c 2006-08-29 14:56:51.000000000 +1000
    @@ -648,6 +648,26 @@ static int raid10_issue_flush(request_qu
    return ret;
    }

    +static int raid10_congested(void *data, int bits)
    +{
    + mddev_t *mddev = data;
    + conf_t *conf = mddev_to_conf(mddev);
    + int i, ret = 0;
    +
    + rcu_read_lock();
    + for (i = 0; i < mddev->raid_disks && ret == 0; i++) {
    + mdk_rdev_t *rdev = rcu_dereference(conf->mirrors[i].rdev);
    + if (rdev && !test_bit(Faulty, &rdev->flags)) {
    + request_queue_t *q = bdev_get_queue(rdev->bdev);
    +
    + ret |= bdi_congested(&q->backing_dev_info, bits);
    + }
    + }
    + rcu_read_unlock();
    + return ret;
    +}
    +
    +
    /* Barriers....
    * Sometimes we need to suspend IO while we do something else,
    * either some resync/recovery, or reconfigure the array.
    @@ -2094,6 +2114,8 @@ static int run(mddev_t *mddev)

    mddev->queue->unplug_fn = raid10_unplug;
    mddev->queue->issue_flush_fn = raid10_issue_flush;
    + mddev->queue->backing_dev_info.congested_fn = raid10_congested;
    + mddev->queue->backing_dev_info.congested_data = mddev;

    /* Calculate max read-ahead size.
    * We need to readahead at least twice a whole stripe....
    -
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