# \[Patch v1 4/4\] md/raid5: Fix rmw/rcw parametrization check

- From: \<hidden\>
- Date: 2015-08-07 20:21:04 
- List: linux-raid
- Page: https://ratatoskr.run/linux-raid/2015/08/6630205
- Thread: https://ratatoskr.run/linux-raid/2015/08/6630205/t.md

```text
md/raid5: Fix rmw/rcw parametrization check

Commit 584acdd49cd2472ca0f5a06adbe979db82d0b4af (activate rmw feature) and
commit d06f191f8ecaef4d524e765fdb455f96392fbd42 (rmw_level) allow to set the
desired rmw/rcw handling for a raid456 device. For the corner case that IO 
costs of rmw and rcw are equal setting PARITY_PREFER_RMW should favour rmw 
over rcw. The implementation is slightly messed. Instead the default setting
PARITY_ENABLE_RMW already favours rmw. Fix that.

Signed-off-by: Markus Stockhausen <redacted>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index f8630c1..f94c389 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3564,7 +3564,7 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 		/* Calculate the real rcw later - for now make it
 		 * look like rcw is cheaper
 		 */
-		rcw = 1; rmw = 2;
+		rcw = 1; rmw = 3;
 		pr_debug("force RCW rmw_level=%u, recovery_cp=%llu sh->sector=%llu\n",
 			 conf->rmw_level, (unsigned long long)recovery_cp,
 			 (unsigned long long)sh->sector);
@@ -3584,7 +3584,9 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 	}
 	pr_debug("for sector %llu, rmw=%d rcw=%d\n",
 		(unsigned long long)sh->sector, rmw, rcw);
-	if ((rmw < rcw || (rmw == rcw && conf->rmw_level == PARITY_ENABLE_RMW)) && rmw > 0) {
+	if (rcw && conf->rmw_level == PARITY_PREFER_RMW)
+		rcw++;
+	if (rmw && rmw < rcw) {
 		/* prefer read-modify-write, but need to get some data */
 		if (conf->mddev->queue)
 			blk_add_trace_msg(conf->mddev->queue,
@@ -3611,7 +3613,7 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 			}
 		}
 	}
-	if ((rcw < rmw || (rcw == rmw && conf->rmw_level != PARITY_ENABLE_RMW)) && rcw > 0) {
+	if (rcw && rcw <= rmw) {
 		/* want reconstruct write, but need to get some data */
 		int qread =0;
 		rcw = 0;


```

## Attachments

- [InterScan\_Disclaimer.txt](https://ratatoskr.run/linux-raid/2015/08/6630205/attachment/0) (text/plain, 1694 bytes)