[Devel] [PATCH rh7 10/12] ploop: Set up discard limits

[Kirill Tkhai]

Logical neighbouring blocks usually are not physically
neighbours, so we may issue discard only for a single
block. Thus, we request block layer to split discard
requests in (1 << (cluster_log + 9)) bytes bios.

This is the basis. Later we may introduce some performance
improvements for corner cases on top of this.

Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 drivers/block/ploop/dev.c       |    6 +++---
 drivers/block/ploop/io_direct.c |    1 +
 drivers/block/ploop/io_kaio.c   |    5 +----
 include/linux/ploop/ploop.h     |   11 +++++++++++
 4 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/drivers/block/ploop/dev.c b/drivers/block/ploop/dev.c
index 9ac436201b1b..bf508a9b1bc8 100644
--- a/drivers/block/ploop/dev.c
+++ b/drivers/block/ploop/dev.c
@@ -4026,10 +4026,10 @@ static int ploop_start(struct ploop_device * plo, struct block_device *bdev)
 	blk_queue_merge_bvec(q, ploop_merge_bvec);
 	blk_queue_flush(q, REQ_FLUSH);
 
-	if (top_delta->io.ops->queue_settings)
-		top_delta->io.ops->queue_settings(&top_delta->io, q);
+	top_delta->io.ops->queue_settings(&top_delta->io, q);
+	/* REQ_WRITE_SAME is not supported */
+	blk_queue_max_write_same_sectors(q, 0);
 
-	blk_queue_max_discard_sectors(q, INT_MAX);
 	queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
 	queue_flag_clear_unlocked(QUEUE_FLAG_STANDBY, q);
 
diff --git a/drivers/block/ploop/io_direct.c b/drivers/block/ploop/io_direct.c
index b0d7095864fc..18563eaa4f1a 100644
--- a/drivers/block/ploop/io_direct.c
+++ b/drivers/block/ploop/io_direct.c
@@ -1776,6 +1776,7 @@ static int dio_congested(struct ploop_io * io, int bits)
 
 static void dio_queue_settings(struct ploop_io * io, struct request_queue * q)
 {
+	ploop_set_discard_limits(io->plo);
 	blk_queue_stack_limits(q, bdev_get_queue(io->files.bdev));
 }
 
diff --git a/drivers/block/ploop/io_kaio.c b/drivers/block/ploop/io_kaio.c
index f5d9936d4cd4..84da1cec5643 100644
--- a/drivers/block/ploop/io_kaio.c
+++ b/drivers/block/ploop/io_kaio.c
@@ -1078,10 +1078,7 @@ static void kaio_unplug(struct ploop_io * io)
 static void kaio_queue_settings(struct ploop_io * io, struct request_queue * q)
 {
 	blk_set_stacking_limits(&q->limits);
-	blk_queue_max_write_same_sectors(q, 0);
-
-	q->limits.discard_alignment = PAGE_SIZE;
-	q->limits.discard_granularity = PAGE_SIZE;
+	ploop_set_discard_limits(io->plo);
 }
 
 static void kaio_issue_flush(struct ploop_io * io, struct ploop_request *preq)
diff --git a/include/linux/ploop/ploop.h b/include/linux/ploop/ploop.h
index 71a55573bdf6..b209c9f096a8 100644
--- a/include/linux/ploop/ploop.h
+++ b/include/linux/ploop/ploop.h
@@ -853,6 +853,17 @@ static inline bool whole_block(struct ploop_device * plo, struct ploop_request *
 	return !(preq->req_sector & (cluster_size_in_sec(plo) - 1));
 }
 
+static inline void ploop_set_discard_limits(struct ploop_device *plo)
+{
+	struct request_queue *q = plo->queue;
+	/*
+	 * In PLOOP_FMT_PLOOP1 format, neighbouring virtual clusters
+	 * are not neighbours on backed device, so we expect block
+	 * subsystem splits discards in single-cluster requests.
+	 */
+	q->limits.discard_granularity = cluster_size_in_bytes(plo);
+	q->limits.max_discard_sectors = (1 << plo->cluster_log);
+}
 struct map_node;
 
 int ploop_fastmap(struct ploop_map * map, cluster_t block, iblock_t *result);