drbd: Introduce new disk config option rs-discard-granularity

As long as the value is 0 the feature is disabled. With setting
it to a positive value, DRBD limits and aligns its resync requests
to the rs-discard-granularity setting. If the sync source detects
all zeros in such a block, the resync target discards the range
on disk.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 29 insertions, 3 deletions

diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index fad03e4feef6..99339dfe4389 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -1348,12 +1348,38 @@ static bool write_ordering_changed(struct disk_conf *a, struct disk_conf *b)
                 a->disk_drain != b->disk_drain;
 }
 
-static void sanitize_disk_conf(struct disk_conf *disk_conf, struct drbd_backing_dev *nbc)
+static void sanitize_disk_conf(struct drbd_device *device, struct disk_conf *disk_conf,
+                               struct drbd_backing_dev *nbc)
 {
+        struct request_queue * const q = nbc->backing_bdev->bd_disk->queue;
+
         if (disk_conf->al_extents < DRBD_AL_EXTENTS_MIN)
                 disk_conf->al_extents = DRBD_AL_EXTENTS_MIN;
         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 (disk_conf->rs_discard_granularity) {
+                int orig_value = disk_conf->rs_discard_granularity;
+                int remainder;
+
+                if (q->limits.discard_granularity > disk_conf->rs_discard_granularity)
+                        disk_conf->rs_discard_granularity = q->limits.discard_granularity;
+
+                remainder = disk_conf->rs_discard_granularity % q->limits.discard_granularity;
+                disk_conf->rs_discard_granularity += remainder;
+
+                if (disk_conf->rs_discard_granularity > q->limits.max_discard_sectors << 9)
+                        disk_conf->rs_discard_granularity = q->limits.max_discard_sectors << 9;
+
+                if (disk_conf->rs_discard_granularity != orig_value)
+                        drbd_info(device, "rs_discard_granularity changed to %d\n",
+                                  disk_conf->rs_discard_granularity);
+        }
 }
 
 int drbd_adm_disk_opts(struct sk_buff *skb, struct genl_info *info)
@@ -1403,7 +1429,7 @@ int drbd_adm_disk_opts(struct sk_buff *skb, struct genl_info *info)
         if (!expect(new_disk_conf->resync_rate >= 1))
                 new_disk_conf->resync_rate = 1;
 
-        sanitize_disk_conf(new_disk_conf, device->ldev);
+        sanitize_disk_conf(device, new_disk_conf, device->ldev);
 
         if (new_disk_conf->c_plan_ahead > DRBD_C_PLAN_AHEAD_MAX)
                 new_disk_conf->c_plan_ahead = DRBD_C_PLAN_AHEAD_MAX;
@@ -1698,7 +1724,7 @@ int drbd_adm_attach(struct sk_buff *skb, struct genl_info *info)
         if (retcode != NO_ERROR)
                 goto fail;
 
-        sanitize_disk_conf(new_disk_conf, nbc);
+        sanitize_disk_conf(device, new_disk_conf, nbc);
 
         if (drbd_get_max_capacity(nbc) < new_disk_conf->disk_size) {
                 drbd_err(device, "max capacity %llu smaller than disk size %llu\n",