[PATCH 3.17 21/73] dm cache: only use overwrite optimisation for promotion when in writeback mode

From: Greg Kroah-Hartman
Date: Tue Jan 06 2015 - 21:38:51 EST


3.17-stable review patch. If anyone has any objections, please let me know.

------------------

From: Joe Thornber <ejt@xxxxxxxxxx>

commit f29a3147e251d7ae20d3194ff67f109d71e501b4 upstream.

Overwrite causes the cache block and origin blocks to diverge, which
is only allowed in writeback mode.

Signed-off-by: Joe Thornber <ejt@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
drivers/md/dm-cache-target.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -1070,7 +1070,8 @@ static void issue_copy(struct dm_cache_m

avoid = is_discarded_oblock(cache, mg->new_oblock);

- if (!avoid && bio_writes_complete_block(cache, bio)) {
+ if (writeback_mode(&cache->features) &&
+ !avoid && bio_writes_complete_block(cache, bio)) {
issue_overwrite(mg, bio);
return;
}


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