On Thu, 24 Sep 2020, Mike Snitzer wrote:
> On Thu, Sep 24 2020 at 10:34am -0400,
> Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
>
> > Hi Mike
> >
> > Could you send this to Linus before v5.9 is released?
> >
> > Mikulas
> >
> >
> >
> > From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> >
> > If q->limits.discard_granularity is zero, the block core will warn in
> > __blkdev_issue_discard. This patch sets it to a minimum - 512 bytes.
> >
> > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> > Fixes: b35fd7422c2f ("block: check queue's limits.discard_granularity in __blkdev_issue_discard()")
> > Fixes: 9b15d109a6b2 ("block: improve discard bio alignment in __blkdev_issue_discard()")
> > Fixes: c52abf563049 ("loop: Better discard support for block devices")
> >
> > ---
> > drivers/md/dm-table.c | 5 ++++-
> > 1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > Index: linux-2.6/drivers/md/dm-table.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/md/dm-table.c 2020-08-31 12:08:27.000000000 +0200
> > +++ linux-2.6/drivers/md/dm-table.c 2020-09-24 16:23:55.000000000 +0200
> > @@ -1858,8 +1858,11 @@ void dm_table_set_restrictions(struct dm
> > q->limits.discard_granularity = 0;
> > q->limits.discard_alignment = 0;
> > q->limits.discard_misaligned = 0;
> > - } else
> > + } else {
> > blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
> > + if (q->limits.discard_granularity < 512)
> > + q->limits.discard_granularity = 512;
> > + }
> >
> > if (dm_table_supports_secure_erase(t))
> > blk_queue_flag_set(QUEUE_FLAG_SECERASE, q);
>
> This patch is wrong, papers over something else. Please identify what
> that something else is.
>
> block core has _always_ cheecked if discard_granularity is non-zero to
> allow discards.
>
> Why is q->limits.discard_granularity < 512 if discard is supported by
> the DM table and targets?
>
> That shouldn't ever be.
>
> Mike
OK
I'm sending another patch that changes the function raid_io_hints. This is
where the zero came from.
Mikulas
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