linux-kernel - [PATCH 20/30] drbd: discard_zeroes_if_aligned allows "thin" resync for discard_zeroes

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Date:	Tue, 14 Jun 2016 00:26:29 +0200
From:	Philipp Reisner <philipp.reisner@...bit.com>
To:	Jens Axboe <axboe@...com>, linux-kernel@...r.kernel.org
Cc:	drbd-dev@...ts.linbit.com
Subject: [PATCH 20/30] drbd: discard_zeroes_if_aligned allows "thin" resync for discard_zeroes_data=0

From: Lars Ellenberg <lars@...bit.com>

Even if discard_zeroes_data != 0,
if discard_zeroes_if_aligned is set, we assume we can reliably
zero-out/discard using the drbd_issue_peer_discard() helper.

Signed-off-by: Philipp Reisner <philipp.reisner@...bit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@...bit.com>
---
 drivers/block/drbd/drbd_nl.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index e5fdcc6..169e3e1 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -1408,9 +1408,12 @@ static void sanitize_disk_conf(struct drbd_device *device, struct disk_conf *dis
 	if (disk_conf->al_extents > drbd_al_extents_max(nbc))
 		disk_conf->al_extents = drbd_al_extents_max(nbc);
 
-	if (!blk_queue_discard(q) || !q->limits.discard_zeroes_data) {
-		disk_conf->rs_discard_granularity = 0; /* disable feature */
-		drbd_info(device, "rs_discard_granularity feature disabled\n");
+	if (!blk_queue_discard(q)
+	    || (!q->limits.discard_zeroes_data && !disk_conf->discard_zeroes_if_aligned)) {
+		if (disk_conf->rs_discard_granularity) {
+			disk_conf->rs_discard_granularity = 0; /* disable feature */
+			drbd_info(device, "rs_discard_granularity feature disabled\n");
+		}
 	}
 
 	if (disk_conf->rs_discard_granularity) {
-- 
2.7.4