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dm: skip second flush on bio unsupported error

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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>
This commit is contained in:
Mikulas Patocka 2010-08-12 04:14:00 +01:00 committed by Alasdair G Kergon
parent 87c961cb74
commit 708e929513
1 changed files with 13 additions and 2 deletions
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15
drivers/md/dm.c
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@ -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)