Merge branch 'for-2.6.39/stack-plug' into for-2.6.39/core

Conflicts:
	block/blk-core.c
	block/blk-flush.c
	drivers/md/raid1.c
	drivers/md/raid10.c
	drivers/md/raid5.c
	fs/nilfs2/btnode.c
	fs/nilfs2/mdt.c

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

10 files changed, 323 insertions, 315 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 74d496ccf4d7..e1fcf7a24668 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -27,6 +27,7 @@
 #include <linux/writeback.h>
 #include <linux/task_io_accounting_ops.h>
 #include <linux/fault-inject.h>
+#include <linux/list_sort.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/block.h>
@@ -198,135 +199,43 @@ void blk_dump_rq_flags(struct request *rq, char *msg)
 EXPORT_SYMBOL(blk_dump_rq_flags);
 
 /*
- * "plug" the device if there are no outstanding requests: this will
- * force the transfer to start only after we have put all the requests
- * on the list.
- *
- * This is called with interrupts off and no requests on the queue and
- * with the queue lock held.
- */
-void blk_plug_device(struct request_queue *q)
+ * Make sure that plugs that were pending when this function was entered,
+ * are now complete and requests pushed to the queue.
+*/
+static inline void queue_sync_plugs(struct request_queue *q)
 {
-        WARN_ON(!irqs_disabled());
-
         /*
-         * don't plug a stopped queue, it must be paired with blk_start_queue()
-         * which will restart the queueing
+         * If the current process is plugged and has barriers submitted,
+         * we will livelock if we don't unplug first.
          */
-        if (blk_queue_stopped(q))
-                return;
-
-        if (!queue_flag_test_and_set(QUEUE_FLAG_PLUGGED, q)) {
-                mod_timer(&q->unplug_timer, jiffies + q->unplug_delay);
-                trace_block_plug(q);
-        }
-}
-EXPORT_SYMBOL(blk_plug_device);
-
-/**
- * blk_plug_device_unlocked - plug a device without queue lock held
- * @q:    The &struct request_queue to plug
- *
- * Description:
- *   Like @blk_plug_device(), but grabs the queue lock and disables
- *   interrupts.
- **/
-void blk_plug_device_unlocked(struct request_queue *q)
-{
-        unsigned long flags;
-
-        spin_lock_irqsave(q->queue_lock, flags);
-        blk_plug_device(q);
-        spin_unlock_irqrestore(q->queue_lock, flags);
-}
-EXPORT_SYMBOL(blk_plug_device_unlocked);
-
-/*
- * remove the queue from the plugged list, if present. called with
- * queue lock held and interrupts disabled.
- */
-int blk_remove_plug(struct request_queue *q)
-{
-        WARN_ON(!irqs_disabled());
-
-        if (!queue_flag_test_and_clear(QUEUE_FLAG_PLUGGED, q))
-                return 0;
-
-        del_timer(&q->unplug_timer);
-        return 1;
+        blk_flush_plug(current);
 }
-EXPORT_SYMBOL(blk_remove_plug);
 
-/*
- * remove the plug and let it rip..
- */
-void __generic_unplug_device(struct request_queue *q)
+static void blk_delay_work(struct work_struct *work)
 {
-        if (unlikely(blk_queue_stopped(q)))
-                return;
-        if (!blk_remove_plug(q) && !blk_queue_nonrot(q))
-                return;
+        struct request_queue *q;
 
-        q->request_fn(q);
+        q = container_of(work, struct request_queue, delay_work.work);
+        spin_lock_irq(q->queue_lock);
+        __blk_run_queue(q, false);
+        spin_unlock_irq(q->queue_lock);
 }
 
 /**
- * generic_unplug_device - fire a request queue
- * @q:    The &struct request_queue in question
+ * blk_delay_queue - restart queueing after defined interval
+ * @q:          The &struct request_queue in question
+ * @msecs:      Delay in msecs
  *
  * Description:
- *   Linux uses plugging to build bigger requests queues before letting
- *   the device have at them. If a queue is plugged, the I/O scheduler
- *   is still adding and merging requests on the queue. Once the queue
- *   gets unplugged, the request_fn defined for the queue is invoked and
- *   transfers started.
- **/
-void generic_unplug_device(struct request_queue *q)
-{
-        if (blk_queue_plugged(q)) {
-                spin_lock_irq(q->queue_lock);
-                __generic_unplug_device(q);
-                spin_unlock_irq(q->queue_lock);
-        }
-}
-EXPORT_SYMBOL(generic_unplug_device);
-
-static void blk_backing_dev_unplug(struct backing_dev_info *bdi,
-                                   struct page *page)
-{
-        struct request_queue *q = bdi->unplug_io_data;
-
-        blk_unplug(q);
-}
-
-void blk_unplug_work(struct work_struct *work)
-{
-        struct request_queue *q =
-                container_of(work, struct request_queue, unplug_work);
-
-        trace_block_unplug_io(q);
-        q->unplug_fn(q);
-}
-
-void blk_unplug_timeout(unsigned long data)
-{
-        struct request_queue *q = (struct request_queue *)data;
-
-        trace_block_unplug_timer(q);
-        kblockd_schedule_work(q, &q->unplug_work);
-}
-
-void blk_unplug(struct request_queue *q)
+ *   Sometimes queueing needs to be postponed for a little while, to allow
+ *   resources to come back. This function will make sure that queueing is
+ *   restarted around the specified time.
+ */
+void blk_delay_queue(struct request_queue *q, unsigned long msecs)
 {
-        /*
-         * devices don't necessarily have an ->unplug_fn defined
-         */
-        if (q->unplug_fn) {
-                trace_block_unplug_io(q);
-                q->unplug_fn(q);
-        }
+        schedule_delayed_work(&q->delay_work, msecs_to_jiffies(msecs));
 }
-EXPORT_SYMBOL(blk_unplug);
+EXPORT_SYMBOL(blk_delay_queue);
 
 /**
  * blk_start_queue - restart a previously stopped queue
@@ -362,7 +271,7 @@ EXPORT_SYMBOL(blk_start_queue);
  **/
 void blk_stop_queue(struct request_queue *q)
 {
-        blk_remove_plug(q);
+        cancel_delayed_work(&q->delay_work);
         queue_flag_set(QUEUE_FLAG_STOPPED, q);
 }
 EXPORT_SYMBOL(blk_stop_queue);
@@ -387,9 +296,9 @@ EXPORT_SYMBOL(blk_stop_queue);
  */
 void blk_sync_queue(struct request_queue *q)
 {
-        del_timer_sync(&q->unplug_timer);
         del_timer_sync(&q->timeout);
-        cancel_work_sync(&q->unplug_work);
+        cancel_delayed_work_sync(&q->delay_work);
+        queue_sync_plugs(q);
 }
 EXPORT_SYMBOL(blk_sync_queue);
 
@@ -405,14 +314,9 @@ EXPORT_SYMBOL(blk_sync_queue);
  */
 void __blk_run_queue(struct request_queue *q, bool force_kblockd)
 {
-        blk_remove_plug(q);
-
         if (unlikely(blk_queue_stopped(q)))
                 return;
 
-        if (elv_queue_empty(q))
-                return;
-
         /*
          * Only recurse once to avoid overrunning the stack, let the unplug
          * handling reinvoke the handler shortly if we already got there.
@@ -420,10 +324,8 @@ void __blk_run_queue(struct request_queue *q, bool force_kblockd)
         if (!force_kblockd && !queue_flag_test_and_set(QUEUE_FLAG_REENTER, q)) {
                 q->request_fn(q);
                 queue_flag_clear(QUEUE_FLAG_REENTER, q);
-        } else {
-                queue_flag_set(QUEUE_FLAG_PLUGGED, q);
-                kblockd_schedule_work(q, &q->unplug_work);
-        }
+        } else
+                queue_delayed_work(kblockd_workqueue, &q->delay_work, 0);
 }
 EXPORT_SYMBOL(__blk_run_queue);
 
@@ -517,8 +419,6 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
         if (!q)
                 return NULL;
 
-        q->backing_dev_info.unplug_io_fn = blk_backing_dev_unplug;
-        q->backing_dev_info.unplug_io_data = q;
         q->backing_dev_info.ra_pages =
                         (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
         q->backing_dev_info.state = 0;
@@ -538,13 +438,12 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
 
         setup_timer(&q->backing_dev_info.laptop_mode_wb_timer,
                     laptop_mode_timer_fn, (unsigned long) q);
-        init_timer(&q->unplug_timer);
         setup_timer(&q->timeout, blk_rq_timed_out_timer, (unsigned long) q);
         INIT_LIST_HEAD(&q->timeout_list);
         INIT_LIST_HEAD(&q->flush_queue[0]);
         INIT_LIST_HEAD(&q->flush_queue[1]);
         INIT_LIST_HEAD(&q->flush_data_in_flight);
-        INIT_WORK(&q->unplug_work, blk_unplug_work);
+        INIT_DELAYED_WORK(&q->delay_work, blk_delay_work);
 
         kobject_init(&q->kobj, &blk_queue_ktype);
 
@@ -639,7 +538,6 @@ blk_init_allocated_queue_node(struct request_queue *q, request_fn_proc *rfn,
         q->request_fn           = rfn;
         q->prep_rq_fn           = NULL;
         q->unprep_rq_fn         = NULL;
-        q->unplug_fn            = generic_unplug_device;
         q->queue_flags          = QUEUE_FLAG_DEFAULT;
 
         /* Override internal queue lock with supplied lock pointer */
@@ -677,6 +575,8 @@ int blk_get_queue(struct request_queue *q)
 
 static inline void blk_free_request(struct request_queue *q, struct request *rq)
 {
+        BUG_ON(rq->cmd_flags & REQ_ON_PLUG);
+
         if (rq->cmd_flags & REQ_ELVPRIV)
                 elv_put_request(q, rq);
         mempool_free(rq, q->rq.rq_pool);
@@ -898,8 +798,8 @@ out:
 }
 
 /*
- * No available requests for this queue, unplug the device and wait for some
- * requests to become available.
+ * No available requests for this queue, wait for some requests to become
+ * available.
  *
  * Called with q->queue_lock held, and returns with it unlocked.
  */
@@ -920,7 +820,6 @@ static struct request *get_request_wait(struct request_queue *q, int rw_flags,
 
                 trace_block_sleeprq(q, bio, rw_flags & 1);
 
-                __generic_unplug_device(q);
                 spin_unlock_irq(q->queue_lock);
                 io_schedule();
 
@@ -1042,6 +941,13 @@ void blk_requeue_request(struct request_queue *q, struct request *rq)
 }
 EXPORT_SYMBOL(blk_requeue_request);
 
+static void add_acct_request(struct request_queue *q, struct request *rq,
+                             int where)
+{
+        drive_stat_acct(rq, 1);
+        __elv_add_request(q, rq, where);
+}
+
 /**
  * blk_insert_request - insert a special request into a request queue
  * @q:          request queue where request should be inserted
@@ -1084,8 +990,7 @@ void blk_insert_request(struct request_queue *q, struct request *rq,
         if (blk_rq_tagged(rq))
                 blk_queue_end_tag(q, rq);
 
-        drive_stat_acct(rq, 1);
-        __elv_add_request(q, rq, where, 0);
+        add_acct_request(q, rq, where);
         __blk_run_queue(q, false);
         spin_unlock_irqrestore(q->queue_lock, flags);
 }
@@ -1206,6 +1111,113 @@ void blk_add_request_payload(struct request *rq, struct page *page,
 }
 EXPORT_SYMBOL_GPL(blk_add_request_payload);
 
+static bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
+                                   struct bio *bio)
+{
+        const int ff = bio->bi_rw & REQ_FAILFAST_MASK;
+
+        /*
+         * Debug stuff, kill later
+         */
+        if (!rq_mergeable(req)) {
+                blk_dump_rq_flags(req, "back");
+                return false;
+        }
+
+        if (!ll_back_merge_fn(q, req, bio))
+                return false;
+
+        trace_block_bio_backmerge(q, bio);
+
+        if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
+                blk_rq_set_mixed_merge(req);
+
+        req->biotail->bi_next = bio;
+        req->biotail = bio;
+        req->__data_len += bio->bi_size;
+        req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));
+
+        drive_stat_acct(req, 0);
+        return true;
+}
+
+static bool bio_attempt_front_merge(struct request_queue *q,
+                                    struct request *req, struct bio *bio)
+{
+        const int ff = bio->bi_rw & REQ_FAILFAST_MASK;
+        sector_t sector;
+
+        /*
+         * Debug stuff, kill later
+         */
+        if (!rq_mergeable(req)) {
+                blk_dump_rq_flags(req, "front");
+                return false;
+        }
+
+        if (!ll_front_merge_fn(q, req, bio))
+                return false;
+
+        trace_block_bio_frontmerge(q, bio);
+
+        if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
+                blk_rq_set_mixed_merge(req);
+
+        sector = bio->bi_sector;
+
+        bio->bi_next = req->bio;
+        req->bio = bio;
+
+        /*
+         * may not be valid. if the low level driver said
+         * it didn't need a bounce buffer then it better
+         * not touch req->buffer either...
+         */
+        req->buffer = bio_data(bio);
+        req->__sector = bio->bi_sector;
+        req->__data_len += bio->bi_size;
+        req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));
+
+        drive_stat_acct(req, 0);
+        return true;
+}
+
+/*
+ * Attempts to merge with the plugged list in the current process. Returns
+ * true if merge was succesful, otherwise false.
+ */
+static bool attempt_plug_merge(struct task_struct *tsk, struct request_queue *q,
+                               struct bio *bio)
+{
+        struct blk_plug *plug;
+        struct request *rq;
+        bool ret = false;
+
+        plug = tsk->plug;
+        if (!plug)
+                goto out;
+
+        list_for_each_entry_reverse(rq, &plug->list, queuelist) {
+                int el_ret;
+
+                if (rq->q != q)
+                        continue;
+
+                el_ret = elv_try_merge(rq, bio);
+                if (el_ret == ELEVATOR_BACK_MERGE) {
+                        ret = bio_attempt_back_merge(q, rq, bio);
+                        if (ret)
+                                break;
+                } else if (el_ret == ELEVATOR_FRONT_MERGE) {
+                        ret = bio_attempt_front_merge(q, rq, bio);
+                        if (ret)
+                                break;
+                }
+        }
+out:
+        return ret;
+}
+
 void init_request_from_bio(struct request *req, struct bio *bio)
 {
         req->cpu = bio->bi_comp_cpu;
@@ -1221,26 +1233,12 @@ void init_request_from_bio(struct request *req, struct bio *bio)
         blk_rq_bio_prep(req->q, req, bio);
 }
 
-/*
- * Only disabling plugging for non-rotational devices if it does tagging
- * as well, otherwise we do need the proper merging
- */
-static inline bool queue_should_plug(struct request_queue *q)
-{
-        return !(blk_queue_nonrot(q) && blk_queue_tagged(q));
-}
-
 static int __make_request(struct request_queue *q, struct bio *bio)
 {
-        struct request *req;
-        int el_ret;
-        unsigned int bytes = bio->bi_size;
-        const unsigned short prio = bio_prio(bio);
         const bool sync = !!(bio->bi_rw & REQ_SYNC);
-        const bool unplug = !!(bio->bi_rw & REQ_UNPLUG);
-        const unsigned long ff = bio->bi_rw & REQ_FAILFAST_MASK;
-        int where = ELEVATOR_INSERT_SORT;
-        int rw_flags;
+        struct blk_plug *plug;
+        int el_ret, rw_flags, where = ELEVATOR_INSERT_SORT;
+        struct request *req;
 
         /*
          * low level driver can indicate that it wants pages above a
@@ -1249,78 +1247,36 @@ static int __make_request(struct request_queue *q, struct bio *bio)
          */
         blk_queue_bounce(q, &bio);
 
-        spin_lock_irq(q->queue_lock);
-
         if (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) {
+                spin_lock_irq(q->queue_lock);
                 where = ELEVATOR_INSERT_FLUSH;
                 goto get_rq;
         }
 
-        if (elv_queue_empty(q))
-                goto get_rq;
-
-        el_ret = elv_merge(q, &req, bio);
-        switch (el_ret) {
-        case ELEVATOR_BACK_MERGE:
-                BUG_ON(!rq_mergeable(req));
-
-                if (!ll_back_merge_fn(q, req, bio))
-                        break;
-
-                trace_block_bio_backmerge(q, bio);
-
-                if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
-                        blk_rq_set_mixed_merge(req);
-
-                req->biotail->bi_next = bio;
-                req->biotail = bio;
-                req->__data_len += bytes;
-                req->ioprio = ioprio_best(req->ioprio, prio);
-                if (!blk_rq_cpu_valid(req))
-                        req->cpu = bio->bi_comp_cpu;
-                drive_stat_acct(req, 0);
-                elv_bio_merged(q, req, bio);
-                if (!attempt_back_merge(q, req))
-                        elv_merged_request(q, req, el_ret);
+        /*
+         * Check if we can merge with the plugged list before grabbing
+         * any locks.
+         */
+        if (attempt_plug_merge(current, q, bio))
                 goto out;
 
-        case ELEVATOR_FRONT_MERGE:
-                BUG_ON(!rq_mergeable(req));
-
-                if (!ll_front_merge_fn(q, req, bio))
-                        break;
-
-                trace_block_bio_frontmerge(q, bio);
+        spin_lock_irq(q->queue_lock);
 
-                if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff) {
-                        blk_rq_set_mixed_merge(req);
-                        req->cmd_flags &= ~REQ_FAILFAST_MASK;
-                        req->cmd_flags |= ff;
+        el_ret = elv_merge(q, &req, bio);
+        if (el_ret == ELEVATOR_BACK_MERGE) {
+                BUG_ON(req->cmd_flags & REQ_ON_PLUG);
+                if (bio_attempt_back_merge(q, req, bio)) {
+                        if (!attempt_back_merge(q, req))
+                                elv_merged_request(q, req, el_ret);
+                        goto out_unlock;
+                }
+        } else if (el_ret == ELEVATOR_FRONT_MERGE) {
+                BUG_ON(req->cmd_flags & REQ_ON_PLUG);
+                if (bio_attempt_front_merge(q, req, bio)) {
+                        if (!attempt_front_merge(q, req))
+                                elv_merged_request(q, req, el_ret);
+                        goto out_unlock;
                 }
-
-                bio->bi_next = req->bio;
-                req->bio = bio;
-
-                /*
-                 * may not be valid. if the low level driver said
-                 * it didn't need a bounce buffer then it better
-                 * not touch req->buffer either...
-                 */
-                req->buffer = bio_data(bio);
-                req->__sector = bio->bi_sector;
-                req->__data_len += bytes;
-                req->ioprio = ioprio_best(req->ioprio, prio);
-                if (!blk_rq_cpu_valid(req))
-                        req->cpu = bio->bi_comp_cpu;
-                drive_stat_acct(req, 0);
-                elv_bio_merged(q, req, bio);
-                if (!attempt_front_merge(q, req))
-                        elv_merged_request(q, req, el_ret);
-                goto out;
-
-        /* ELV_NO_MERGE: elevator says don't/can't merge. */
-        default:
-                ;
         }
 
 get_rq:
@@ -1347,20 +1303,35 @@ get_rq:
          */
         init_request_from_bio(req, bio);
 
-        spin_lock_irq(q->queue_lock);
         if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) ||
-            bio_flagged(bio, BIO_CPU_AFFINE))
-                req->cpu = blk_cpu_to_group(smp_processor_id());
-        if (queue_should_plug(q) && elv_queue_empty(q))
-                blk_plug_device(q);
-
-        /* insert the request into the elevator */
-        drive_stat_acct(req, 1);
-        __elv_add_request(q, req, where, 0);
+            bio_flagged(bio, BIO_CPU_AFFINE)) {
+                req->cpu = blk_cpu_to_group(get_cpu());
+                put_cpu();
+        }
+
+        plug = current->plug;
+        if (plug) {
+                if (!plug->should_sort && !list_empty(&plug->list)) {
+                        struct request *__rq;
+
+                        __rq = list_entry_rq(plug->list.prev);
+                        if (__rq->q != q)
+                                plug->should_sort = 1;
+                }
+                /*
+                 * Debug flag, kill later
+                 */
+                req->cmd_flags |= REQ_ON_PLUG;
+                list_add_tail(&req->queuelist, &plug->list);
+                drive_stat_acct(req, 1);
+        } else {
+                spin_lock_irq(q->queue_lock);
+                add_acct_request(q, req, where);
+                __blk_run_queue(q, false);
+out_unlock:
+                spin_unlock_irq(q->queue_lock);
+        }
 out:
-        if (unplug || !queue_should_plug(q))
-                __generic_unplug_device(q);
-        spin_unlock_irq(q->queue_lock);
         return 0;
 }
 
@@ -1763,9 +1734,7 @@ int blk_insert_cloned_request(struct request_queue *q, struct request *rq)
          */
         BUG_ON(blk_queued_rq(rq));
 
-        drive_stat_acct(rq, 1);
-        __elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 0);
-
+        add_acct_request(q, rq, ELEVATOR_INSERT_BACK);
         spin_unlock_irqrestore(q->queue_lock, flags);
 
         return 0;
@@ -2643,6 +2612,113 @@ int kblockd_schedule_work(struct request_queue *q, struct work_struct *work)
 }
 EXPORT_SYMBOL(kblockd_schedule_work);
 
+int kblockd_schedule_delayed_work(struct request_queue *q,
+                        struct delayed_work *dwork, unsigned long delay)
+{
+        return queue_delayed_work(kblockd_workqueue, dwork, delay);
+}
+EXPORT_SYMBOL(kblockd_schedule_delayed_work);
+
+#define PLUG_MAGIC      0x91827364
+
+void blk_start_plug(struct blk_plug *plug)
+{
+        struct task_struct *tsk = current;
+
+        plug->magic = PLUG_MAGIC;
+        INIT_LIST_HEAD(&plug->list);
+        plug->should_sort = 0;
+
+        /*
+         * If this is a nested plug, don't actually assign it. It will be
+         * flushed on its own.
+         */
+        if (!tsk->plug) {
+                /*
+                 * Store ordering should not be needed here, since a potential
+                 * preempt will imply a full memory barrier
+                 */
+                tsk->plug = plug;
+        }
+}
+EXPORT_SYMBOL(blk_start_plug);
+
+static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
+{
+        struct request *rqa = container_of(a, struct request, queuelist);
+        struct request *rqb = container_of(b, struct request, queuelist);
+
+        return !(rqa->q == rqb->q);
+}
+
+static void flush_plug_list(struct blk_plug *plug)
+{
+        struct request_queue *q;
+        unsigned long flags;
+        struct request *rq;
+
+        BUG_ON(plug->magic != PLUG_MAGIC);
+
+        if (list_empty(&plug->list))
+                return;
+
+        if (plug->should_sort)
+                list_sort(NULL, &plug->list, plug_rq_cmp);
+
+        q = NULL;
+        local_irq_save(flags);
+        while (!list_empty(&plug->list)) {
+                rq = list_entry_rq(plug->list.next);
+                list_del_init(&rq->queuelist);
+                BUG_ON(!(rq->cmd_flags & REQ_ON_PLUG));
+                BUG_ON(!rq->q);
+                if (rq->q != q) {
+                        if (q) {
+                                __blk_run_queue(q, false);
+                                spin_unlock(q->queue_lock);
+                        }
+                        q = rq->q;
+                        spin_lock(q->queue_lock);
+                }
+                rq->cmd_flags &= ~REQ_ON_PLUG;
+
+                /*
+                 * rq is already accounted, so use raw insert
+                 */
+                __elv_add_request(q, rq, ELEVATOR_INSERT_SORT);
+        }
+
+        if (q) {
+                __blk_run_queue(q, false);
+                spin_unlock(q->queue_lock);
+        }
+
+        BUG_ON(!list_empty(&plug->list));
+        local_irq_restore(flags);
+}
+
+static void __blk_finish_plug(struct task_struct *tsk, struct blk_plug *plug)
+{
+        flush_plug_list(plug);
+
+        if (plug == tsk->plug)
+                tsk->plug = NULL;
+}
+
+void blk_finish_plug(struct blk_plug *plug)
+{
+        if (plug)
+                __blk_finish_plug(current, plug);
+}
+EXPORT_SYMBOL(blk_finish_plug);
+
+void __blk_flush_plug(struct task_struct *tsk, struct blk_plug *plug)
+{
+        __blk_finish_plug(tsk, plug);
+        tsk->plug = plug;
+}
+EXPORT_SYMBOL(__blk_flush_plug);
+
 int __init blk_dev_init(void)
 {
         BUILD_BUG_ON(__REQ_NR_BITS > 8 *
diff --git a/block/blk-exec.c b/block/blk-exec.c
index cf1456a02acd..7482b7fa863b 100644
--- a/block/blk-exec.c
+++ b/block/blk-exec.c
@@ -54,8 +54,8 @@ void blk_execute_rq_nowait(struct request_queue *q, struct gendisk *bd_disk,
         rq->end_io = done;
         WARN_ON(irqs_disabled());
         spin_lock_irq(q->queue_lock);
-        __elv_add_request(q, rq, where, 1);
-        __generic_unplug_device(q);
+        __elv_add_request(q, rq, where);
+        __blk_run_queue(q, false);
         /* the queue is stopped so it won't be plugged+unplugged */
         if (rq->cmd_type == REQ_TYPE_PM_RESUME)
                 q->request_fn(q);
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 0bd8c9c5d6e5..93d5fd8e51eb 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -194,7 +194,6 @@ static void flush_end_io(struct request *flush_rq, int error)
 {
         struct request_queue *q = flush_rq->q;
         struct list_head *running = &q->flush_queue[q->flush_running_idx];
-        bool was_empty = elv_queue_empty(q);
         bool queued = false;
         struct request *rq, *n;
 
@@ -218,7 +217,7 @@ static void flush_end_io(struct request *flush_rq, int error)
          * from request completion path and calling directly into
          * request_fn may confuse the driver.  Always use kblockd.
          */
-        if (queued && was_empty)
+        if (queued)
                 __blk_run_queue(q, true);
 }
 
@@ -269,13 +268,12 @@ static bool blk_kick_flush(struct request_queue *q)
 static void flush_data_end_io(struct request *rq, int error)
 {
         struct request_queue *q = rq->q;
-        bool was_empty = elv_queue_empty(q);
 
         /*
          * After populating an empty queue, kick it to avoid stall.  Read
          * the comment in flush_end_io().
          */
-        if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error) && was_empty)
+        if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error))
                 __blk_run_queue(q, true);
 }
 
diff --git a/block/blk-settings.c b/block/blk-settings.c
index df649fa59ded..1fa769293597 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -164,14 +164,6 @@ void blk_queue_make_request(struct request_queue *q, make_request_fn *mfn)
         blk_queue_congestion_threshold(q);
         q->nr_batching = BLK_BATCH_REQ;
 
-        q->unplug_thresh = 4;           /* hmm */
-        q->unplug_delay = msecs_to_jiffies(3);  /* 3 milliseconds */
-        if (q->unplug_delay == 0)
-                q->unplug_delay = 1;
-
-        q->unplug_timer.function = blk_unplug_timeout;
-        q->unplug_timer.data = (unsigned long)q;
-
         blk_set_default_limits(&q->limits);
         blk_queue_max_hw_sectors(q, BLK_SAFE_MAX_SECTORS);
 
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 32dd3e4b041d..37abbfc68590 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -768,6 +768,7 @@ static int throtl_dispatch(struct request_queue *q)
         unsigned int nr_disp = 0;
         struct bio_list bio_list_on_stack;
         struct bio *bio;
+        struct blk_plug plug;
 
         spin_lock_irq(q->queue_lock);
 
@@ -796,9 +797,10 @@ out:
          * immediate dispatch
          */
         if (nr_disp) {
+                blk_start_plug(&plug);
                 while((bio = bio_list_pop(&bio_list_on_stack)))
                         generic_make_request(bio);
-                blk_unplug(q);
+                blk_finish_plug(&plug);
         }
         return nr_disp;
 }
diff --git a/block/blk.h b/block/blk.h
index 284b500852bd..49d21af81d07 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -18,8 +18,6 @@ int blk_rq_append_bio(struct request_queue *q, struct request *rq,
 void blk_dequeue_request(struct request *rq);
 void __blk_queue_free_tags(struct request_queue *q);
 
-void blk_unplug_work(struct work_struct *work);
-void blk_unplug_timeout(unsigned long data);
 void blk_rq_timed_out_timer(unsigned long data);
 void blk_delete_timer(struct request *);
 void blk_add_timer(struct request *);
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9697053f80bc..c826ef81c679 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -500,13 +500,6 @@ static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
         }
 }
 
-static int cfq_queue_empty(struct request_queue *q)
-{
-        struct cfq_data *cfqd = q->elevator->elevator_data;
-
-        return !cfqd->rq_queued;
-}
-
 /*
  * Scale schedule slice based on io priority. Use the sync time slice only
  * if a queue is marked sync and has sync io queued. A sync queue with async
@@ -4080,7 +4073,6 @@ static struct elevator_type iosched_cfq = {
                 .elevator_add_req_fn =          cfq_insert_request,
                 .elevator_activate_req_fn =     cfq_activate_request,
                 .elevator_deactivate_req_fn =   cfq_deactivate_request,
-                .elevator_queue_empty_fn =      cfq_queue_empty,
                 .elevator_completed_req_fn =    cfq_completed_request,
                 .elevator_former_req_fn =       elv_rb_former_request,
                 .elevator_latter_req_fn =       elv_rb_latter_request,
diff --git a/block/deadline-iosched.c b/block/deadline-iosched.c
index b547cbca7b23..5139c0ea1864 100644
--- a/block/deadline-iosched.c
+++ b/block/deadline-iosched.c
@@ -326,14 +326,6 @@ dispatch_request:
         return 1;
 }
 
-static int deadline_queue_empty(struct request_queue *q)
-{
-        struct deadline_data *dd = q->elevator->elevator_data;
-
-        return list_empty(&dd->fifo_list[WRITE])
-                && list_empty(&dd->fifo_list[READ]);
-}
-
 static void deadline_exit_queue(struct elevator_queue *e)
 {
         struct deadline_data *dd = e->elevator_data;
@@ -445,7 +437,6 @@ static struct elevator_type iosched_deadline = {
                 .elevator_merge_req_fn =        deadline_merged_requests,
                 .elevator_dispatch_fn =         deadline_dispatch_requests,
                 .elevator_add_req_fn =          deadline_add_request,
-                .elevator_queue_empty_fn =      deadline_queue_empty,
                 .elevator_former_req_fn =       elv_rb_former_request,
                 .elevator_latter_req_fn =       elv_rb_latter_request,
                 .elevator_init_fn =             deadline_init_queue,
diff --git a/block/elevator.c b/block/elevator.c
index fabf3675c913..542ce826b401 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -113,7 +113,7 @@ int elv_rq_merge_ok(struct request *rq, struct bio *bio)
 }
 EXPORT_SYMBOL(elv_rq_merge_ok);
 
-static inline int elv_try_merge(struct request *__rq, struct bio *bio)
+int elv_try_merge(struct request *__rq, struct bio *bio)
 {
         int ret = ELEVATOR_NO_MERGE;
 
@@ -421,6 +421,8 @@ void elv_dispatch_sort(struct request_queue *q, struct request *rq)
         struct list_head *entry;
         int stop_flags;
 
+        BUG_ON(rq->cmd_flags & REQ_ON_PLUG);
+
         if (q->last_merge == rq)
                 q->last_merge = NULL;
 
@@ -617,21 +619,12 @@ void elv_quiesce_end(struct request_queue *q)
 
 void elv_insert(struct request_queue *q, struct request *rq, int where)
 {
-        int unplug_it = 1;
-
         trace_block_rq_insert(q, rq);
 
         rq->q = q;
 
         switch (where) {
         case ELEVATOR_INSERT_REQUEUE:
-                /*
-                 * Most requeues happen because of a busy condition,
-                 * don't force unplug of the queue for that case.
-                 * Clear unplug_it and fall through.
-                 */
-                unplug_it = 0;
-
         case ELEVATOR_INSERT_FRONT:
                 rq->cmd_flags |= REQ_SOFTBARRIER;
                 list_add(&rq->queuelist, &q->queue_head);
@@ -677,25 +670,17 @@ void elv_insert(struct request_queue *q, struct request *rq, int where)
                 rq->cmd_flags |= REQ_SOFTBARRIER;
                 blk_insert_flush(rq);
                 break;
-
         default:
                 printk(KERN_ERR "%s: bad insertion point %d\n",
                        __func__, where);
                 BUG();
         }
-
-        if (unplug_it && blk_queue_plugged(q)) {
-                int nrq = q->rq.count[BLK_RW_SYNC] + q->rq.count[BLK_RW_ASYNC]
-                                - queue_in_flight(q);
-
-                if (nrq >= q->unplug_thresh)
-                        __generic_unplug_device(q);
-        }
 }
 
-void __elv_add_request(struct request_queue *q, struct request *rq, int where,
-                       int plug)
+void __elv_add_request(struct request_queue *q, struct request *rq, int where)
 {
+        BUG_ON(rq->cmd_flags & REQ_ON_PLUG);
+
         if (rq->cmd_flags & REQ_SOFTBARRIER) {
                 /* barriers are scheduling boundary, update end_sector */
                 if (rq->cmd_type == REQ_TYPE_FS ||
@@ -707,38 +692,20 @@ void __elv_add_request(struct request_queue *q, struct request *rq, int where,
                     where == ELEVATOR_INSERT_SORT)
                 where = ELEVATOR_INSERT_BACK;
 
-        if (plug)
-                blk_plug_device(q);
-
         elv_insert(q, rq, where);
 }
 EXPORT_SYMBOL(__elv_add_request);
 
-void elv_add_request(struct request_queue *q, struct request *rq, int where,
-                     int plug)
+void elv_add_request(struct request_queue *q, struct request *rq, int where)
 {
         unsigned long flags;
 
         spin_lock_irqsave(q->queue_lock, flags);
-        __elv_add_request(q, rq, where, plug);
+        __elv_add_request(q, rq, where);
         spin_unlock_irqrestore(q->queue_lock, flags);
 }
 EXPORT_SYMBOL(elv_add_request);
 
-int elv_queue_empty(struct request_queue *q)
-{
-        struct elevator_queue *e = q->elevator;
-
-        if (!list_empty(&q->queue_head))
-                return 0;
-
-        if (e->ops->elevator_queue_empty_fn)
-                return e->ops->elevator_queue_empty_fn(q);
-
-        return 1;
-}
-EXPORT_SYMBOL(elv_queue_empty);
-
 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
 {
         struct elevator_queue *e = q->elevator;
diff --git a/block/noop-iosched.c b/block/noop-iosched.c
index 232c4b38cd37..06389e9ef96d 100644
--- a/block/noop-iosched.c
+++ b/block/noop-iosched.c
@@ -39,13 +39,6 @@ static void noop_add_request(struct request_queue *q, struct request *rq)
         list_add_tail(&rq->queuelist, &nd->queue);
 }
 
-static int noop_queue_empty(struct request_queue *q)
-{
-        struct noop_data *nd = q->elevator->elevator_data;
-
-        return list_empty(&nd->queue);
-}
-
 static struct request *
 noop_former_request(struct request_queue *q, struct request *rq)
 {
@@ -90,7 +83,6 @@ static struct elevator_type elevator_noop = {
                 .elevator_merge_req_fn          = noop_merged_requests,
                 .elevator_dispatch_fn           = noop_dispatch,
                 .elevator_add_req_fn            = noop_add_request,
-                .elevator_queue_empty_fn        = noop_queue_empty,
                 .elevator_former_req_fn         = noop_former_request,
                 .elevator_latter_req_fn         = noop_latter_request,
                 .elevator_init_fn               = noop_init_queue,