Hi
This patch removes the second cache flush if discard isn't supported.
The first flush is hard to bypass, so it's not worth doing it.
Mikulas
---
Don't do the second flush if the request isn't supported.
If the request fails with -EOPNOTSUPP, don't perform the second flush.
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.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---
drivers/md/dm.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
Index: linux-2.6.35-rc3-fast/drivers/md/dm.c
===================================================================
--- linux-2.6.35-rc3-fast.orig/drivers/md/dm.c 2010-07-08 00:11:05.000000000 +0200
+++ linux-2.6.35-rc3-fast/drivers/md/dm.c 2010-07-08 00:12:02.000000000 +0200
@@ -2365,7 +2365,12 @@ static void process_barrier(struct mappe
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)
--
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