dm kcopyd: call copy offload with asynchronous callback

Change dm kcopyd so that it calls blkdev_issue_copy with an asynchronous
callback. There can be large number of pending kcopyd requests and holding
a process context for each of them may put too much load on the workqueue
subsystem.

This patch changes it so that blkdev_issue_copy returns after it submitted
the requests and copy_offload_callback is called when the copy operation
finishes.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm-kcopyd.c |   32 ++++++++++++++------------------
 1 file changed, 14 insertions(+), 18 deletions(-)

Index: linux-4.11-rc2/drivers/md/dm-kcopyd.c
===================================================================
--- linux-4.11-rc2.orig/drivers/md/dm-kcopyd.c
+++ linux-4.11-rc2/drivers/md/dm-kcopyd.c
@@ -361,8 +361,6 @@ struct kcopyd_job {
 	sector_t progress;
 
 	struct kcopyd_job *master_job;
-
-	struct work_struct copy_work;
 };
 
 static struct kmem_cache *_job_cache;
@@ -629,8 +627,9 @@ static void segment_complete(int read_er
 	struct kcopyd_job *sub_job = (struct kcopyd_job *) context;
 	struct kcopyd_job *job = sub_job->master_job;
 	struct dm_kcopyd_client *kc = job->kc;
+	unsigned long flags;
 
-	spin_lock(&job->lock);
+	spin_lock_irqsave(&job->lock, flags);
 
 	/* update the error */
 	if (read_err)
@@ -654,7 +653,7 @@ static void segment_complete(int read_er
 			job->progress += count;
 		}
 	}
-	spin_unlock(&job->lock);
+	spin_unlock_irqrestore(&job->lock, flags);
 
 	if (count) {
 		int i;
@@ -715,28 +714,25 @@ static void submit_job(struct kcopyd_job
 	}
 }
 
-static void copy_offload_work(struct work_struct *work)
+static void copy_offload_callback(void *ptr, int error)
 {
-	struct kcopyd_job *job = container_of(work, struct kcopyd_job, copy_work);
-	sector_t copied;
+	struct kcopyd_job *job = ptr;
 
-	blkdev_issue_copy(job->source.bdev, job->source.sector,
-			  job->dests[0].bdev, job->dests[0].sector,
-			  job->source.count, &copied, NULL, NULL,
-			  GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
-
-	job->source.sector += copied;
-	job->source.count -= copied;
-	job->dests[0].sector += copied;
-	job->dests[0].count -= copied;
+	job->source.sector += job->progress;
+	job->source.count -= job->progress;
+	job->dests[0].sector += job->progress;
+	job->dests[0].count -= job->progress;
 
 	submit_job(job);
 }
 
 static void try_copy_offload(struct kcopyd_job *job)
 {
-	INIT_WORK(&job->copy_work, copy_offload_work);
-	queue_work(job->kc->kcopyd_wq, &job->copy_work);
+	blkdev_issue_copy(job->source.bdev, job->source.sector,
+			  job->dests[0].bdev, job->dests[0].sector,
+			  job->source.count, &job->progress,
+			  copy_offload_callback, job,
+			  GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
 }
 
 int dm_kcopyd_copy(struct dm_kcopyd_client *kc, struct dm_io_region *from,