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authorMikulas Patocka <mpatocka@redhat.com>2010-08-12 04:14:00 +0100
committerAlasdair G Kergon <agk@redhat.com>2010-08-12 04:14:00 +0100
commit708e929513502fb050c0a3c3ee267cab5b056ded (patch)
treee7b6845a3d53c5b92350f1755b4e89418f0c351c /drivers/md/dm.c
parent87c961cb747fa55b664b76abfcb9d44c14ae851f (diff)
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>
Diffstat (limited to 'drivers/md/dm.c')
-rw-r--r--drivers/md/dm.c15
1 files changed, 13 insertions, 2 deletions
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index a503b95ecbf..f3cc5d99fe8 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -639,8 +639,14 @@ static void dec_pending(struct dm_io *io, int error)
* 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 @@ static void process_barrier(struct mapped_device *md, struct bio *bio)
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)