dm: skip second flush on bio unsupported error
When processing barriers, skip the second flush if processing the bio
failed with -EOPNOTSUPP. This can happen with discard+barrier requests.
If the device doesn't support discard, there would be two useless
SYNCHRONIZE CACHE commands. The first dm_flush cannot be so easily
optimized out, so we leave it there.
Previously, -EOPNOTSUPP could be received in dec_pending only with empty
barriers and we ignored that error, assuming the device not supporting
cache flushes has cache always consistent. With the addition of discard
barriers, this -EOPNOTSUPP can also be generated by discards and we
must record it in md->barrier_error for process_barrier.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index a503b95..f3cc5d9 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -639,8 +639,14 @@
* There can be just one barrier request so we use
* a per-device variable for error reporting.
* Note that you can't touch the bio after end_io_acct
+ *
+ * We ignore -EOPNOTSUPP for empty flush reported by
+ * underlying devices. We assume that if the device
+ * doesn't support empty barriers, it doesn't need
+ * cache flushing commands.
*/
- if (!md->barrier_error && io_error != -EOPNOTSUPP)
+ if (!md->barrier_error &&
+ !(bio_empty_barrier(bio) && io_error == -EOPNOTSUPP))
md->barrier_error = io_error;
end_io_acct(io);
free_io(md, io);
@@ -2284,7 +2290,12 @@
if (!bio_empty_barrier(bio)) {
__split_and_process_bio(md, bio);
- dm_flush(md);
+ /*
+ * If the request isn't supported, don't waste time with
+ * the second flush.
+ */
+ if (md->barrier_error != -EOPNOTSUPP)
+ dm_flush(md);
}
if (md->barrier_error != DM_ENDIO_REQUEUE)