Bryan Gurney reported a series of I/O errors resulting from using
CFQ with a host-managed SMR disk. After commit 39051dd85f28 ("scsi:
sd: Remove zone write locking), which was merged in 4.16, users
should use one of the deadline I/O schedulers (unless applications
are very careful about only submitting 1 I/O per zone). Change our
defaults to provide a working configuration.
Reported-by: Bryan Gurney <bgurney@xxxxxxxxxx>
Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
---
block/blk-sysfs.c | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index d00d1b0..ec2f29b 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -908,6 +908,30 @@ int blk_register_queue(struct gendisk *disk)
return ret;
}
}
+
+ /*
+ * Temporary work-around for host-managed SMR devices: right now,
+ * the deadline I/O schedulers are the only ones that are SMR-
+ * aware. Use of other schedulers will almost always result
+ * in I/O errors due to out-of-order writes to zones. For now,
+ * force deadline if we can. The eventual goal is to get rid
+ * of this in favor of a dispatch layer that would work with
+ * all I/O schedulers.
+ */
+ if (blk_queue_zoned_model(q) == BLK_ZONED_HM) {
+ ret = __elevator_change(q, "deadline", false);
+ if (ret == 0)
+ printk("%s: switched to deadline I/O scheduler for "
+ "host-managed SMR device %s\n", __func__,
+ disk->disk_name);
+ else {
+ printk("%s: warning: unable to switch to SMR-aware "
+ "deadline I/O scheduler for host-managed SMR "
+ "device %s\n", __func__, disk->disk_name);
+ printk("Consider building deadline and mq-deadline "
+ "into your kernel (not as modules)\n");
+ }
+ }
ret = 0;
unlock:
mutex_unlock(&q->sysfs_lock);
--
2.8.2.335.g4bb51ae
