* How can need dm use limits.max_hw_sectors from the bdev?
@ 2016-01-17 6:34 Eric Wheeler
2016-01-18 15:56 ` Mike Snitzer
0 siblings, 1 reply; 3+ messages in thread
From: Eric Wheeler @ 2016-01-17 6:34 UTC (permalink / raw)
To: dm-devel
Hello all,
I'm writing a trivial dm target and hitting errors like this:
io too big device loop0 (2048 > 255)
which looks like the problem described here:
https://bugzilla.kernel.org/show_bug.cgi?id=9401#c3
and is is consistent:
cat /sys/block/loop0/queue/max_hw_sectors_kb
127
# cat /sys/block/dm-4/queue/max_hw_sectors_kb
2147483647
By tracing from sysfs it looks like I need to do something like this when
called from the target constructor (dm_ctr_fn target_type.ctr) function:
target->table->md->queue->limits.max_hw_sectors =
priv->dm_dev_bdev->bdev->bd_queue->limits.max_hw_sectors;
but I cannot because `struct md` and `struct mapped_device` are opaque
which makes me think there is a better (correct) way to do this. Is there a way
to change my target device's max_hw_sectors value to 127?
Is there some other generic solution?
Would late bio splitting solve this?
-Eric
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: How can need dm use limits.max_hw_sectors from the bdev?
2016-01-17 6:34 How can need dm use limits.max_hw_sectors from the bdev? Eric Wheeler
@ 2016-01-18 15:56 ` Mike Snitzer
2016-01-20 3:00 ` How can " Eric Wheeler
0 siblings, 1 reply; 3+ messages in thread
From: Mike Snitzer @ 2016-01-18 15:56 UTC (permalink / raw)
To: Eric Wheeler; +Cc: dm-devel
On Sun, Jan 17 2016 at 1:34am -0500,
Eric Wheeler <dm-devel@lists.ewheeler.net> wrote:
> Hello all,
>
> I'm writing a trivial dm target and hitting errors like this:
> io too big device loop0 (2048 > 255)
>
> which looks like the problem described here:
> https://bugzilla.kernel.org/show_bug.cgi?id=9401#c3
>
> and is is consistent:
> cat /sys/block/loop0/queue/max_hw_sectors_kb
> 127
> # cat /sys/block/dm-4/queue/max_hw_sectors_kb
> 2147483647
>
> By tracing from sysfs it looks like I need to do something like this when
> called from the target constructor (dm_ctr_fn target_type.ctr) function:
>
> target->table->md->queue->limits.max_hw_sectors =
> priv->dm_dev_bdev->bdev->bd_queue->limits.max_hw_sectors;
>
> but I cannot because `struct md` and `struct mapped_device` are opaque
> which makes me think there is a better (correct) way to do this. Is there a way
> to change my target device's max_hw_sectors value to 127?
>
> Is there some other generic solution?
You'll first want to implement the .iterate_devices hook. This alone
should enable DM core to leverage the block layer's blk_stack_limits()
infrastructure to stack up your top-level device's queue_limits.
And if you'd like to override your device's queue_limits beyond what is
stacked up from the underlying device(s) you can implement the .io_hints
hook in your target.
> Would late bio splitting solve this?
Maybe, if by solve this you mean: the block core won't error any more.
But you're better off stacking underlying devices' queue_limits like I
detailed above.
Mike
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: How can dm use limits.max_hw_sectors from the bdev?
2016-01-18 15:56 ` Mike Snitzer
@ 2016-01-20 3:00 ` Eric Wheeler
0 siblings, 0 replies; 3+ messages in thread
From: Eric Wheeler @ 2016-01-20 3:00 UTC (permalink / raw)
To: device-mapper development
On Mon, 18 Jan 2016, Mike Snitzer wrote:
> On Sun, Jan 17 2016 at 1:34am -0500,
> Eric Wheeler <dm-devel@lists.ewheeler.net> wrote:
>
> > Hello all,
> >
> > I'm writing a trivial dm target and hitting errors like this:
> > io too big device loop0 (2048 > 255)
> >
> > which looks like the problem described here:
> > https://bugzilla.kernel.org/show_bug.cgi?id=9401#c3
> >
> > and is consistent:
> > cat /sys/block/loop0/queue/max_hw_sectors_kb
> > 127
> > # cat /sys/block/dm-4/queue/max_hw_sectors_kb
> > 2147483647
> >
> > By tracing from sysfs it looks like I need to do something like this when
> > called from the target constructor (dm_ctr_fn target_type.ctr) function:
> >
> > target->table->md->queue->limits.max_hw_sectors =
> > priv->dm_dev_bdev->bdev->bd_queue->limits.max_hw_sectors;
> >
> > but I cannot because `struct md` and `struct mapped_device` are opaque
> > which makes me think there is a better (correct) way to do this. Is there a way
> > to change my target device's max_hw_sectors value to 127?
> >
> > Is there some other generic solution?
>
> You'll first want to implement the .iterate_devices hook. This alone
> should enable DM core to leverage the block layer's blk_stack_limits()
> infrastructure to stack up your top-level device's queue_limits.
>
> And if you'd like to override your device's queue_limits beyond what is
> stacked up from the underlying device(s) you can implement the .io_hints
> hook in your target.
That did it. Thank you!
-Eric
> > Would late bio splitting solve this?
>
> Maybe, if by solve this you mean: the block core won't error any more.
> But you're better off stacking underlying devices' queue_limits like I
> detailed above.
>
> Mike
>
> --
> dm-devel mailing list
> dm-devel@redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel
>
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2016-01-20 3:00 UTC | newest]
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2016-01-17 6:34 How can need dm use limits.max_hw_sectors from the bdev? Eric Wheeler
2016-01-18 15:56 ` Mike Snitzer
2016-01-20 3:00 ` How can " Eric Wheeler
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