dm kcopyd: support copy offload

This patch adds copy offload support to dm-kcopyd. If copy offload fails,
copying is performed using dm-io, just like before.

There is a module parameter "copy_offload" that can be set to enable or
disable this feature. It can be used to test performance of copy offload.

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

---
 drivers/md/dm-kcopyd.c |   38 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

Index: linux-3.16-rc5/drivers/md/dm-kcopyd.c
===================================================================
--- linux-3.16-rc5.orig/drivers/md/dm-kcopyd.c	2014-07-15 16:18:15.000000000 +0200
+++ linux-3.16-rc5/drivers/md/dm-kcopyd.c	2014-07-15 19:20:34.000000000 +0200
@@ -96,6 +96,9 @@ static DEFINE_SPINLOCK(throttle_spinlock
  */
 #define MAX_SLEEPS			10
 
+static bool copy_offload = true;
+module_param(copy_offload, bool, S_IRUGO | S_IWUSR);
+
 static void io_job_start(struct dm_kcopyd_throttle *t)
 {
 	unsigned throttle, now, difference;
@@ -358,6 +361,8 @@ struct kcopyd_job {
 	sector_t progress;
 
 	struct kcopyd_job *master_job;
+
+	struct work_struct copy_work;
 };
 
 static struct kmem_cache *_job_cache;
@@ -709,6 +714,31 @@ static void submit_job(struct kcopyd_job
 	}
 }
 
+static void copy_offload_work(struct work_struct *work)
+{
+	struct kcopyd_job *job = container_of(work, struct kcopyd_job, copy_work);
+	sector_t copied;
+
+	blkdev_issue_copy(job->source.bdev, job->source.sector,
+			  job->dests[0].bdev, job->dests[0].sector,
+			  job->source.count,
+			  GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN,
+			  NULL, NULL, &copied);
+
+	job->source.sector += copied;
+	job->source.count -= copied;
+	job->dests[0].sector += copied;
+	job->dests[0].count -= copied;
+
+	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);
+}
+
 int dm_kcopyd_copy(struct dm_kcopyd_client *kc, struct dm_io_region *from,
 		   unsigned int num_dests, struct dm_io_region *dests,
 		   unsigned int flags, dm_kcopyd_notify_fn fn, void *context)
@@ -757,7 +787,13 @@ int dm_kcopyd_copy(struct dm_kcopyd_clie
 	job->context = context;
 	job->master_job = job;
 
-	submit_job(job);
+	if (copy_offload && num_dests == 1 &&
+	    bdev_copy_offload(job->source.bdev) &&
+	    bdev_copy_offload(job->dests[0].bdev)) {
+		try_copy_offload(job);
+	} else {
+		submit_job(job);
+	}
 
 	return 0;
 }