Re: [PATCH v6 4/5] dm-thin: Add REQ_OP_PROVISION support

Mike Snitzer
2023-05-12T17:33:34Z

On Sat, May 06 2023 at 2:29P -0400,
Sarthak Kukreti <sarthakkukreti@chromium.org> wrote:

> dm-thinpool uses the provision request to provision
> blocks for a dm-thin device. dm-thinpool currently does not
> pass through REQ_OP_PROVISION to underlying devices.
>
> For shared blocks, provision requests will break sharing and copy the
> contents of the entire block. Additionally, if 'skip_block_zeroing'
> is not set, dm-thin will opt to zero out the entire range as a part
> of provisioning.
>
> Signed-off-by: Sarthak Kukreti <sarthakkukreti@chromium.org>
> ---
> drivers/md/dm-thin.c | 70 +++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 66 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
> index 2b13c949bd72..3f94f53ac956 100644
> --- a/drivers/md/dm-thin.c
> +++ b/drivers/md/dm-thin.c
...
> @@ -4114,6 +4171,8 @@ static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
> * The pool uses the same discard limits as the underlying data
> * device. DM core has already set this up.
> */
> +
> + limits->max_provision_sectors = pool->sectors_per_block;

Just noticed that setting limits->max_provision_sectors needs to move
above pool_io_hints code that sets up discards -- otherwise the early
return from if (!pt->adjusted_pf.discard_enabled) will cause setting
max_provision_sectors to be skipped.

Here is a roll up of the fixes that need to be folded into this patch:

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 3f94f53ac956..90c8e36cb327 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -4151,6 +4151,8 @@ static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
blk_limits_io_opt(limits, pool->sectors_per_block << SECTOR_SHIFT);
}

+ limits->max_provision_sectors = pool->sectors_per_block;
+
/*
* pt->adjusted_pf is a staging area for the actual features to use.
* They get transferred to the live pool in bind_control_target()
@@ -4171,8 +4173,6 @@ static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
* The pool uses the same discard limits as the underlying data
* device. DM core has already set this up.
*/
-
- limits->max_provision_sectors = pool->sectors_per_block;
}

static struct target_type pool_target = {
@@ -4349,6 +4349,7 @@ static int thin_ctr(struct dm_target *ti, unsigned int argc, char **argv)

ti->num_provision_bios = 1;
ti->provision_supported = true;
+ ti->max_provision_granularity = true;

mutex_unlock(&dm_thin_pool_table.mutex);