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Subject[PATCH 2/2] Initialize mempool and elevator only for request-based dm devices
Date
Intialize the request_queue and elevator only when the device is marked as
a request-based device. This avoids unnecessary creation of mempool for
requests. Also we wrongly initialize the elevator even for bio-based devices.
As the /sys/block/dm-*/queue/scheduler is exported for device-mapper devices,
it is possible to confuse with scheduler options for bio-based devices where
scheduler is not at all used.

Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>

---
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 8a311ea..b01dfbe 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1749,22 +1749,21 @@ static struct mapped_device *alloc_dev(int minor)
INIT_LIST_HEAD(&md->uevent_list);
spin_lock_init(&md->uevent_lock);

- md->queue = blk_init_queue(dm_request_fn, NULL);
+ md->queue = blk_alloc_queue(GFP_KERNEL);
if (!md->queue)
goto bad_queue;

/*
* Request-based dm devices cannot be stacked on top of bio-based dm
- * devices. The type of this dm device has not been decided yet,
- * although we initialized the queue using blk_init_queue().
+ * devices. The type of this dm device has not been decided yet.
* The type is decided at the first table loading time.
* To prevent problematic device stacking, clear the queue flag
* for request stacking support until then.
*
* This queue is new, so no concurrency on the queue_flags.
*/
+ md->queue->queue_flags = QUEUE_FLAG_DEFAULT;
queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, md->queue);
- md->saved_make_request_fn = md->queue->make_request_fn;
md->queue->queuedata = md;
md->queue->backing_dev_info.congested_fn = dm_any_congested;
md->queue->backing_dev_info.congested_data = md;
@@ -1772,9 +1771,6 @@ static struct mapped_device *alloc_dev(int minor)
blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
md->queue->unplug_fn = dm_unplug_all;
blk_queue_merge_bvec(md->queue, dm_merge_bvec);
- blk_queue_softirq_done(md->queue, dm_softirq_done);
- blk_queue_prep_rq(md->queue, dm_prep_fn);
- blk_queue_lld_busy(md->queue, dm_lld_busy);

md->disk = alloc_disk(1);
if (!md->disk)
@@ -2203,7 +2199,25 @@ int dm_swap_table(struct mapped_device *md, struct dm_table *table)
goto out;
}

- __unbind(md);
+ if (md->map)
+ __unbind(md);
+ else {
+ /* new device is being marked as either request-based or bio-based */
+ if (dm_table_request_based(table)) {
+ /* Initialize queue for request-based dm */
+ r = blk_init_allocated_queue(md->queue, dm_request_fn,
+ NULL);
+ if (r)
+ goto out;
+ md->saved_make_request_fn = md->queue->make_request_fn;
+ blk_queue_make_request(md->queue, dm_request);
+ blk_queue_softirq_done(md->queue, dm_softirq_done);
+ blk_queue_prep_rq(md->queue, dm_prep_fn);
+ blk_queue_lld_busy(md->queue, dm_lld_busy);
+
+ }
+ }
+
r = __bind(md, table, &limits);

out:


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