On Tue, Jan 21 2020 at  5:42am -0500,
Kirill Tkhai [off-list ref] wrote:

Since dm inherits limits from underlining block devices,
this patch directly disables max_allocate_sectors for dm
till full allocation support is implemented.

This prevents high-level primitives (generic_make_request_checks(),
__blkdev_issue_write_zeroes(), ...) from sending REQ_ALLOCATE
requests.

Signed-off-by: Kirill Tkhai <redacted>
---
 drivers/md/dm-table.c |    2 ++
 drivers/md/md.h       |    1 +
 2 files changed, 3 insertions(+)

You're mixing DM and MD changes in the same patch.

But I'm wondering if it might be best to set this default for stacking
devices in blk_set_stacking_limits()?

And then it is up to each stacking driver to override as needed.

Mike