[dm-devel] [dm-6.4 PATCH v3 13/20] dm: split discards further if target sets max_discard_granularity

Mike Snitzer
2023-03-27T20:14:03Z

The block core (bio_split_discard) will already split discards based
on the 'discard_granularity' and 'max_discard_sectors' queue_limits.
But the DM thin target also needs to ensure that it doesn't receive a
discard that spans a 'max_discard_sectors' boundary.

Introduce a dm_target 'max_discard_granularity' flag that if set will
cause DM core to split discard bios relative to 'max_discard_sectors'.
This treats 'discard_granularity' as a "min_discard_granularity" and
'max_discard_sectors' as a "max_discard_granularity".

Requested-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
---
drivers/md/dm.c | 25 +++++++++++++++++++------
include/linux/device-mapper.h | 6 ++++++
include/uapi/linux/dm-ioctl.h | 4 ++--
3 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index b6ace995b9ca..6eb0748a3bb2 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1162,7 +1162,8 @@ static inline sector_t max_io_len_target_boundary(struct dm_target *ti,
return ti->len - target_offset;
}

-static sector_t max_io_len(struct dm_target *ti, sector_t sector)
+static sector_t __max_io_len(struct dm_target *ti, sector_t sector,
+ unsigned int max_granularity)
{
sector_t target_offset = dm_target_offset(ti, sector);
sector_t len = max_io_len_target_boundary(ti, target_offset);
@@ -1173,11 +1174,16 @@ static sector_t max_io_len(struct dm_target *ti, sector_t sector)
* explains why stacked chunk_sectors based splitting via
* bio_split_to_limits() isn't possible here.
*/
- if (!ti->max_io_len)
+ if (!max_granularity)
return len;
return min_t(sector_t, len,
min(queue_max_sectors(ti->table->md->queue),
- blk_chunk_sectors_left(target_offset, ti->max_io_len)));
+ blk_chunk_sectors_left(target_offset, max_granularity)));
+}
+
+static inline sector_t max_io_len(struct dm_target *ti, sector_t sector)
+{
+ return __max_io_len(ti, sector, ti->max_io_len);
}

int dm_set_target_max_io_len(struct dm_target *ti, sector_t len)
@@ -1562,12 +1568,13 @@ static void __send_empty_flush(struct clone_info *ci)
}

static void __send_changing_extent_only(struct clone_info *ci, struct dm_target *ti,
- unsigned int num_bios)
+ unsigned int num_bios,
+ unsigned int max_granularity)
{
unsigned int len, bios;

len = min_t(sector_t, ci->sector_count,
- max_io_len_target_boundary(ti, dm_target_offset(ti, ci->sector)));
+ __max_io_len(ti, ci->sector, max_granularity));

atomic_add(num_bios, &ci->io->io_count);
bios = __send_duplicate_bios(ci, ti, num_bios, &len);
@@ -1603,10 +1610,16 @@ static blk_status_t __process_abnormal_io(struct clone_info *ci,
struct dm_target *ti)
{
unsigned int num_bios = 0;
+ unsigned int max_granularity = 0;

switch (bio_op(ci->bio)) {
case REQ_OP_DISCARD:
num_bios = ti->num_discard_bios;
+ if (ti->max_discard_granularity) {
+ struct queue_limits *limits =
+ dm_get_queue_limits(ti->table->md);
+ max_granularity = limits->max_discard_sectors;
+ }
break;
case REQ_OP_SECURE_ERASE:
num_bios = ti->num_secure_erase_bios;
@@ -1627,7 +1640,7 @@ static blk_status_t __process_abnormal_io(struct clone_info *ci,
if (unlikely(!num_bios))
return BLK_STS_NOTSUPP;

- __send_changing_extent_only(ci, ti, num_bios);
+ __send_changing_extent_only(ci, ti, num_bios, max_granularity);
return BLK_STS_OK;
}

diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 7975483816e4..8aa6b3ea91fa 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -358,6 +358,12 @@ struct dm_target {
*/
bool discards_supported:1;

+ /*
+ * Set if this target requires that discards be split on both
+ * 'discard_granularity' and 'max_discard_sectors' boundaries.
+ */
+ bool max_discard_granularity:1;
+
/*
* Set if we need to limit the number of in-flight bios when swapping.
*/
diff --git a/include/uapi/linux/dm-ioctl.h b/include/uapi/linux/dm-ioctl.h
index 7edf335778ba..1990b5700f69 100644
--- a/include/uapi/linux/dm-ioctl.h
+++ b/include/uapi/linux/dm-ioctl.h
@@ -286,9 +286,9 @@ enum {
#define DM_DEV_SET_GEOMETRY _IOWR(DM_IOCTL, DM_DEV_SET_GEOMETRY_CMD, struct dm_ioctl)

#define DM_VERSION_MAJOR 4
-#define DM_VERSION_MINOR 47
+#define DM_VERSION_MINOR 48
#define DM_VERSION_PATCHLEVEL 0
-#define DM_VERSION_EXTRA "-ioctl (2022-07-28)"
+#define DM_VERSION_EXTRA "-ioctl (2023-03-01)"

/* Status bits */
#define DM_READONLY_FLAG (1 << 0) /* In/Out */