On Mon, May 20, 2024 at 11:39:14AM -0400, Mike Snitzer wrote:
> On Mon, May 20, 2024 at 05:06:53PM +0200, Christoph Hellwig wrote:
>
> > This is probably my fault, I actually found this right at the time
> > of the original revert of switching dm to the limits API, and then
> > let it slip as the patch was reverted. That fact that you readded
> > the commit somehow went past my attention window.
>
> It's fine, all we can do now is work through how best to fix it. Open
> to suggestions. But this next hunk, which you trimmed in your reply,
> _seems_ needed to actually fix the issue Ted reported -- given the
> current validate method in blk-settings.c (resharing here to just
> continue this thread in a natural way):
>
> diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
> index 4793ad2aa1f7..c196f39579af 100644
> --- a/drivers/md/dm-thin.c
> +++ b/drivers/md/dm-thin.c
> @@ -4497,7 +4499,8 @@ static void thin_io_hints(struct dm_target *ti, struct
> queue_limits *limits)
>
> if (pool->pf.discard_enabled) {
> limits->discard_granularity = pool->sectors_per_block <<
> SECTOR_SHIFT;
> - limits->max_discard_sectors = pool->sectors_per_block *
> BIO_PRISON_MAX_RANGE;
> + limits->max_hw_discard_sectors =
> limits->max_user_discard_sectors =
> + pool->sectors_per_block * BIO_PRISON_MAX_RANGE;
> }
> }
>
>
Maybe update blk_validate_limits() to ensure max_discard_sectors is a
factor of discard_granularity?
That way thin_io_hints() (and equivalent functions in other DM
targets) just need to be audited/updated to ensure they are setting
both discard_granularity and max_hw_discard_sectors?
Mike
