On 21.01.2020 15:36, Kirill Tkhai wrote:

On 21.01.2020 15:24, Mike Snitzer wrote:

quoted

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

quoted

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.

Hm. Sound like a good idea. This "lim->max_allocate_sectors = 0" in blk_set_stacking_limits()
should work for dm's dm_calculate_queue_limits(), since it calls blk_stack_limits(), which is:

	t->max_allocate_sectors = min(t->max_allocate_sectors,
				      b->max_allocate_sectors);

Could you please tell is this fix is also enough for md?

It looks like it's enough since queue defaults are set in md_alloc()->blk_set_stacking_limits().
In case of we set "max_allocate_sectors = 0", in further it can be changed only manually,
but nobody does this.