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    SubjectRe: [PATCH 05/10] block: remove per-queue plugging
    On Sat, Jan 22, 2011 at 01:17:24AM +0000, Jens Axboe wrote:

    [..]
    > mm/page-writeback.c | 2 +-
    > mm/readahead.c | 12 ---
    > mm/shmem.c | 1 -
    > mm/swap_state.c | 5 +-
    > mm/swapfile.c | 37 --------
    > mm/vmscan.c | 2 +-
    > 118 files changed, 153 insertions(+), 1248 deletions(-)

    block/blk-throttle.c also uses blk_unplug(). We need to get rid of that
    also.

    [..]
    > @@ -632,8 +630,6 @@ void elv_insert(struct request_queue *q, struct request *rq, int where)
    > * don't force unplug of the queue for that case.
    > * Clear unplug_it and fall through.
    > */

    Above comments now seem to be redundant.

    > - unplug_it = 0;
    > -
    > case ELEVATOR_INSERT_FRONT:
    > rq->cmd_flags |= REQ_SOFTBARRIER;
    > list_add(&rq->queuelist, &q->queue_head);

    [..]
    > /*
    > diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
    > index b9e1e15..5ef136c 100644
    > --- a/drivers/md/dm-raid.c
    > +++ b/drivers/md/dm-raid.c
    > @@ -394,7 +394,7 @@ static void raid_unplug(struct dm_target_callbacks *cb)
    > {
    > struct raid_set *rs = container_of(cb, struct raid_set, callbacks);
    >
    > - md_raid5_unplug_device(rs->md.private);
    > + md_raid5_kick_device(rs->md.private);

    With all the unplug logic gone, I think we can get rid of blk_sync_queue()
    call from md. It looks like md was syncing the queue just to make sure
    that unplug_fn is not called again. Now all that logic is gone so it
    should be redundant.

    Also we can probably get rid of some queue_lock taking instances in
    md code. NeilBrown recently put following patch in, which is taking
    queue lock only around plug functions. Now queue plugging gone,
    I guess it should not be required.

    commit da9cf5050a2e3dbc3cf26a8d908482eb4485ed49
    Author: NeilBrown <neilb@suse.de>
    Date: Mon Feb 21 18:25:57 2011 +1100

    md: avoid spinlock problem in blk_throtl_exit

    Thanks
    Vivek

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