dm table: set flush capability based on underlying devices
DM has always advertised both REQ_FLUSH and REQ_FUA flush capabilities
regardless of whether or not a given DM device's underlying devices
also advertised a need for them.
Block's flush-merge changes from 2.6.39 have proven to be more costly
for DM devices. Performance regressions have been reported even when
DM's underlying devices do not advertise that they have a write cache.
Fix the performance regressions by configuring a DM device's flushing
capabilities based on those of the underlying devices' capabilities.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 259ce99..986b875 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1248,9 +1248,45 @@
blk_get_integrity(template_disk));
}
+static int device_flush_capable(struct dm_target *ti, struct dm_dev *dev,
+ sector_t start, sector_t len, void *data)
+{
+ unsigned flush = (*(unsigned *)data);
+ struct request_queue *q = bdev_get_queue(dev->bdev);
+
+ return q && (q->flush_flags & flush);
+}
+
+static bool dm_table_supports_flush(struct dm_table *t, unsigned flush)
+{
+ struct dm_target *ti;
+ unsigned i = 0;
+
+ /*
+ * Require at least one underlying device to support flushes.
+ * t->devices includes internal dm devices such as mirror logs
+ * so we need to use iterate_devices here, which targets
+ * supporting flushes must provide.
+ */
+ while (i < dm_table_get_num_targets(t)) {
+ ti = dm_table_get_target(t, i++);
+
+ if (!ti->num_flush_requests)
+ continue;
+
+ if (ti->type->iterate_devices &&
+ ti->type->iterate_devices(ti, device_flush_capable, &flush))
+ return 1;
+ }
+
+ return 0;
+}
+
void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
struct queue_limits *limits)
{
+ unsigned flush = 0;
+
/*
* Copy table's limits to the DM device's request_queue
*/
@@ -1261,6 +1297,13 @@
else
queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
+ if (dm_table_supports_flush(t, REQ_FLUSH)) {
+ flush |= REQ_FLUSH;
+ if (dm_table_supports_flush(t, REQ_FUA))
+ flush |= REQ_FUA;
+ }
+ blk_queue_flush(q, flush);
+
dm_table_set_integrity(t);
/*