dm: optimize dm_mq_queue_rq to _not_ use kthread if using pure blk-mq

dm_mq_queue_rq() is in atomic context so care must be taken to not
sleep -- as such GFP_ATOMIC is used for the md->bs bioset allocations
and dm-mpath's call to blk_get_request().  In the future the bioset
allocations will hopefully go away (by removing support for partial
completions of bios in a cloned request).

Also prepare for supporting DM blk-mq ontop of old-style request_fn
device(s) if a new dm-mod 'use_blk_mq' parameter is set.  The kthread
will still be used to queue work if blk-mq is used ontop of old-style
request_fn device(s).

Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index c8f07e5..6395347 100644 (file)
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -428,7 +428,7 @@ static int __multipath_map(struct dm_target *ti, struct request *clone,
        } else {
                /* blk-mq request-based interface */
                *__clone = blk_get_request(bdev_get_queue(bdev),
-                                          rq_data_dir(rq), GFP_KERNEL);
+                                          rq_data_dir(rq), GFP_ATOMIC);
                if (IS_ERR(*__clone))
                        /* ENOMEM, requeue */
                        return r;

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 3a66baa..55cadb1 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1077,9 +1077,10 @@ static void free_rq_clone(struct request *clone)
 
        blk_rq_unprep_clone(clone);
 
-       if (clone->q && clone->q->mq_ops)
+       if (clone->q->mq_ops)
                tio->ti->type->release_clone_rq(clone);
-       else
+       else if (!md->queue->mq_ops)
+               /* request_fn queue stacked on request_fn queue(s) */
                free_clone_request(md, clone);
 
        if (!md->queue->mq_ops)
@@ -1838,15 +1839,25 @@ static int setup_clone(struct request *clone, struct request *rq,
 static struct request *clone_rq(struct request *rq, struct mapped_device *md,
                                struct dm_rq_target_io *tio, gfp_t gfp_mask)
 {
-       struct request *clone = alloc_clone_request(md, gfp_mask);
+       /*
+        * Do not allocate a clone if tio->clone was already set
+        * (see: dm_mq_queue_rq).
+        */
+       bool alloc_clone = !tio->clone;
+       struct request *clone;
 
-       if (!clone)
-               return NULL;
+       if (alloc_clone) {
+               clone = alloc_clone_request(md, gfp_mask);
+               if (!clone)
+                       return NULL;
+       } else
+               clone = tio->clone;
 
        blk_rq_init(NULL, clone);
        if (setup_clone(clone, rq, tio, gfp_mask)) {
                /* -ENOMEM */
-               free_clone_request(md, clone);
+               if (alloc_clone)
+                       free_clone_request(md, clone);
                return NULL;
        }
 
@@ -1864,7 +1875,8 @@ static void init_tio(struct dm_rq_target_io *tio, struct request *rq,
        tio->orig = rq;
        tio->error = 0;
        memset(&tio->info, 0, sizeof(tio->info));
-       init_kthread_work(&tio->work, map_tio_request);
+       if (md->kworker_task)
+               init_kthread_work(&tio->work, map_tio_request);
 }
 
 static struct dm_rq_target_io *prep_tio(struct request *rq,
@@ -1941,7 +1953,7 @@ static int map_request(struct dm_rq_target_io *tio, struct request *rq,
                }
                if (IS_ERR(clone))
                        return DM_MAPIO_REQUEUE;
-               if (setup_clone(clone, rq, tio, GFP_NOIO)) {
+               if (setup_clone(clone, rq, tio, GFP_ATOMIC)) {
                        /* -ENOMEM */
                        ti->type->release_clone_rq(clone);
                        return DM_MAPIO_REQUEUE;
@@ -2408,7 +2420,7 @@ static void __bind_mempools(struct mapped_device *md, struct dm_table *t)
        p->bs = NULL;
 
 out:
-       /* mempool bind completed, now no need any mempools in the table */
+       /* mempool bind completed, no longer need any mempools in the table */
        dm_table_free_md_mempools(t);
 }
 
@@ -2713,9 +2725,24 @@ static int dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
        /* Init tio using md established in .init_request */
        init_tio(tio, rq, md);
 
-       /* Establish tio->ti before queuing work (map_tio_request) */
+       /*
+        * Establish tio->ti before queuing work (map_tio_request)
+        * or making direct call to map_request().
+        */
        tio->ti = ti;
-       queue_kthread_work(&md->kworker, &tio->work);
+
+       /* Clone the request if underlying devices aren't blk-mq */
+       if (dm_table_get_type(map) == DM_TYPE_REQUEST_BASED) {
+               /* clone request is allocated at the end of the pdu */
+               tio->clone = (void *)blk_mq_rq_to_pdu(rq) + sizeof(struct dm_rq_target_io);
+               if (!clone_rq(rq, md, tio, GFP_ATOMIC))
+                       return BLK_MQ_RQ_QUEUE_BUSY;
+               queue_kthread_work(&md->kworker, &tio->work);
+       } else {
+               /* Direct call is fine since .queue_rq allows allocations */
+               if (map_request(tio, rq, md) == DM_MAPIO_REQUEUE)
+                       dm_requeue_unmapped_original_request(md, rq);
+       }
 
        return BLK_MQ_RQ_QUEUE_OK;
 }
@@ -2729,6 +2756,7 @@ static struct blk_mq_ops dm_mq_ops = {
 
 static int dm_init_request_based_blk_mq_queue(struct mapped_device *md)
 {
+       unsigned md_type = dm_get_md_type(md);
        struct request_queue *q;
        int err;
 
@@ -2738,7 +2766,11 @@ static int dm_init_request_based_blk_mq_queue(struct mapped_device *md)
        md->tag_set.numa_node = NUMA_NO_NODE;
        md->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
        md->tag_set.nr_hw_queues = 1;
-       md->tag_set.cmd_size = sizeof(struct dm_rq_target_io);
+       if (md_type == DM_TYPE_REQUEST_BASED) {
+               /* make the memory for non-blk-mq clone part of the pdu */
+               md->tag_set.cmd_size = sizeof(struct dm_rq_target_io) + sizeof(struct request);
+       } else
+               md->tag_set.cmd_size = sizeof(struct dm_rq_target_io);
        md->tag_set.driver_data = md;
 
        err = blk_mq_alloc_tag_set(&md->tag_set);
@@ -2756,7 +2788,8 @@ static int dm_init_request_based_blk_mq_queue(struct mapped_device *md)
        /* backfill 'mq' sysfs registration normally done in blk_register_queue */
        blk_mq_register_disk(md->disk);
 
-       init_rq_based_worker_thread(md);
+       if (md_type == DM_TYPE_REQUEST_BASED)
+               init_rq_based_worker_thread(md);
 
        return 0;
 
@@ -2876,7 +2909,7 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
        set_bit(DMF_FREEING, &md->flags);
        spin_unlock(&_minor_lock);
 
-       if (dm_request_based(md))
+       if (dm_request_based(md) && md->kworker_task)
                flush_kthread_worker(&md->kworker);
 
        /*
@@ -3130,7 +3163,8 @@ static int __dm_suspend(struct mapped_device *md, struct dm_table *map,
         */
        if (dm_request_based(md)) {
                stop_queue(md->queue);
-               flush_kthread_worker(&md->kworker);
+               if (md->kworker_task)
+                       flush_kthread_worker(&md->kworker);
        }
 
        flush_workqueue(md->wq);