Re: [RFC PATCH v2 4/8] dm: add BLK_FEAT_WRITE_ZEROES_UNMAP support

Benjamin Marzinski
2025-02-10T22:55:41Z

On Sat, Feb 08, 2025 at 11:12:57AM +0800, Zhang Yi wrote:
> On 2025/2/8 6:14, Benjamin Marzinski wrote:
> > On Wed, Jan 15, 2025 at 07:46:33PM +0800, Zhang Yi wrote:
> >> From: Zhang Yi <yi.zhang@huawei.com>
> >>
> >> Set the BLK_FEAT_WRITE_ZEROES_UNMAP feature on stacking queue limits by
> >> default. This feature shall be disabled if any underlying device does
> >> not support it.
> >>
> >> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
> >> ---
> >> drivers/md/dm-table.c | 3 ++-
> >> 1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> >> index bd8b796ae683..58cce31bcc1e 100644
> >> --- a/drivers/md/dm-table.c
> >> +++ b/drivers/md/dm-table.c
> >> @@ -598,7 +598,8 @@ int dm_split_args(int *argc, char ***argvp, char *input)
> >> static void dm_set_stacking_limits(struct queue_limits *limits)
> >> {
> >> blk_set_stacking_limits(limits);
> >> - limits->features |= BLK_FEAT_IO_STAT | BLK_FEAT_NOWAIT | BLK_FEAT_POLL;
> >> + limits->features |= BLK_FEAT_IO_STAT | BLK_FEAT_NOWAIT | BLK_FEAT_POLL |
> >> + BLK_FEAT_WRITE_ZEROES_UNMAP;
> >> }
> >>
> >
> > dm_table_set_restrictions() can set limits->max_write_zeroes_sectors to
> > 0, and it's called after dm_calculate_queue_limits(), which calls
> > blk_stack_limits(). Just to avoid having the BLK_FEAT_WRITE_ZEROES_UNMAP
> > still set while a device's max_write_zeroes_sectors is 0, it seems like
> > you would want to clear it as well if dm_table_set_restrictions() sets
> > limits->max_write_zeroes_sectors to 0.
> >
>
> Hi, Ben!
>
> Yeah, right. Thanks for pointing this out, and I also checked other
> instances in dm where max_write_zeroes_sectors is set to 0, and it seems
> we should also clear BLK_FEAT_WRITE_ZEROES_UNMAP in
> disable_write_zeroes() as well.

Yep. Makes sense.

Thanks
-Ben

>
> Thanks,
> Yi.