BLKZEROOUT on dm devices

BLKZEROOUT on dm devices

[Bharata B Rao]

Hi,

Is BLKZEROOUT ioctl supposed to work on dm devices ? When I try this
ioctl on an LV that sits on a WRITE SAME capable SCSI device, I see
that conventional zeroing is done since the WRITE SAME support isn't
advertised by the dm device.

# lsblk
NAME                             MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
sda                                8:0    0    50G  0 disk
└─mpathb (dm-12)                 252:12   0    50G  0 mpath
  └─ws_vg-lvol0 (dm-11)          252:11   0     1G  0 lvm
sde                                8:64   0    50G  0 disk
└─mpathb (dm-12)                 252:12   0    50G  0 mpath
  └─ws_vg-lvol0 (dm-11)          252:11   0     1G  0 lvm

# cat /sys/block/sda/queue/write_same_max_bytes
268435456
# cat /sys/block/dm-12/queue/write_same_max_bytes
0
# cat /sys/block/dm-11/queue/write_same_max_bytes
0

[root@llmvm02 ~]# cat /sys/dev/block/8\:0/queue/write_same_max_bytes
268435456
[root@llmvm02 ~]# cat /sys/dev/block/252\:12/queue/write_same_max_bytes
0
[root@llmvm02 ~]# cat /sys/dev/block/252\:11/queue/write_same_max_bytes
0

>From commit d54eaa5a0fde0a202e4e91f200f818edcef15bee, I gather that
WRITE SAME is advertised by a dm device if all of its target and
underlying devices support WRITE SAME. Also as per
4f0b70b0479101522b8645ddc1f5ee7137821db3, WRITE SAME is supported for
linear dm devices. Both of these seem to be true in my case, but still
BLKZEROOUT ioctl resorts to conventional zeroing. What am I missing
here ?

Regards,
Bharata.
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[PATCH] dm table: fix logic bug in dm_table_supports_write_same [was: Re: BLKZEROOUT on dm devices]

[Mike Snitzer]

On Tue, Apr 30 2013 at 12:07am -0400,
Bharata B Rao <bharata.rao@gmail.com> wrote:

> Hi,
> 
> Is BLKZEROOUT ioctl supposed to work on dm devices ? When I try this
> ioctl on an LV that sits on a WRITE SAME capable SCSI device, I see
> that conventional zeroing is done since the WRITE SAME support isn't
> advertised by the dm device.
> 
> # lsblk
> NAME                             MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
> sda                                8:0    0    50G  0 disk
> └─mpathb (dm-12)                 252:12   0    50G  0 mpath
>   └─ws_vg-lvol0 (dm-11)          252:11   0     1G  0 lvm
> sde                                8:64   0    50G  0 disk
> └─mpathb (dm-12)                 252:12   0    50G  0 mpath
>   └─ws_vg-lvol0 (dm-11)          252:11   0     1G  0 lvm
> 
> # cat /sys/block/sda/queue/write_same_max_bytes
> 268435456
> # cat /sys/block/dm-12/queue/write_same_max_bytes
> 0
> # cat /sys/block/dm-11/queue/write_same_max_bytes
> 0
> 
> [root@llmvm02 ~]# cat /sys/dev/block/8\:0/queue/write_same_max_bytes
> 268435456
> [root@llmvm02 ~]# cat /sys/dev/block/252\:12/queue/write_same_max_bytes
> 0
> [root@llmvm02 ~]# cat /sys/dev/block/252\:11/queue/write_same_max_bytes
> 0

Sure enough I see the same limits stacking problem you reported:

# modprobe scsi_debug dev_size_mb=100 lbpws=1
...
sd 5:0:0:0: [sdh] Attached SCSI disk

# cat /sys/block/sdh/queue/write_same_max_bytes
33553920
(which reflects scsi_debug's write_same_length default of 0xffff * 512b)

# echo "0 `blockdev --getsz /dev/sdh` linear /dev/sdh 0" | dmsetup create test
# readlink /dev/mapper/test
../dm-4
# cat /sys/block/dm-4/queue/write_same_max_bytes 
0

> From commit d54eaa5a0fde0a202e4e91f200f818edcef15bee, I gather that
> WRITE SAME is advertised by a dm device if all of its target and
> underlying devices support WRITE SAME. Also as per
> 4f0b70b0479101522b8645ddc1f5ee7137821db3, WRITE SAME is supported for
> linear dm devices. Both of these seem to be true in my case, but still
> BLKZEROOUT ioctl resorts to conventional zeroing. What am I missing
> here ?

The first patch of my WRITE SAME patchset that I posted to dm-devel was
tweaked before going upstream:
http://www.redhat.com/archives/dm-devel/2012-December/msg00064.html

Due to iterate_devices disposition to short-circuit if the test func()
returns true, it looks like Alasdair correctly changed 
s/device_write_same_capable/device_not_write_same_capable/ but forgot to
invert the logic of the calling iterate_devices in
dm_table_supports_write_same().

Anyway, this patch fixes things for me:

From: Mike Snitzer <snitzer@redhat.com>
Date: Tue, 30 Apr 2013 12:24:58 -0400
Subject: [PATCH] dm table: fix logic bug in dm_table_supports_write_same

If device_not_write_same_capable() returns true then the iterate_devices
loop in dm_table_supports_write_same() should return false.

Reported-by: Bharata B Rao <bharata.rao@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # v3.8+
---
 drivers/md/dm-table.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 3fe797f..d801682 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1445,7 +1445,7 @@ static bool dm_table_supports_write_same(struct dm_table *t)
 			return false;
 
 		if (!ti->type->iterate_devices ||
-		    !ti->type->iterate_devices(ti, device_not_write_same_capable, NULL))
+		    ti->type->iterate_devices(ti, device_not_write_same_capable, NULL))
 			return false;
 	}
 
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Re: [PATCH] dm table: fix logic bug in dm_table_supports_write_same [was: Re: BLKZEROOUT on dm devices]

[Bharata B Rao]

On Tue, Apr 30, 2013 at 10:02 PM, Mike Snitzer <snitzer@redhat.com> wrote:
> On Tue, Apr 30 2013 at 12:07am -0400,
> Bharata B Rao <bharata.rao@gmail.com> wrote:
>
>>
>> # lsblk
>> NAME                             MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
>> sda                                8:0    0    50G  0 disk
>> └─mpathb (dm-12)                 252:12   0    50G  0 mpath
>>   └─ws_vg-lvol0 (dm-11)          252:11   0     1G  0 lvm
>> sde                                8:64   0    50G  0 disk
>> └─mpathb (dm-12)                 252:12   0    50G  0 mpath
>>   └─ws_vg-lvol0 (dm-11)          252:11   0     1G  0 lvm
>>
>
>
> Anyway, this patch fixes things for me:

Thanks, this fixes the issue for me too. However if LV/VG/PV are
created on multipath device, then WRITE SAME still doesn't get
advertised for the LV. I had to disable multipath and re-create
LV/VG/PV on a normal device (/dev/sda as against /dev/mapper/mapathb)
to get BLKZEROUT working on LV.

>
> From: Mike Snitzer <snitzer@redhat.com>
> Date: Tue, 30 Apr 2013 12:24:58 -0400
> Subject: [PATCH] dm table: fix logic bug in dm_table_supports_write_same
>
> If device_not_write_same_capable() returns true then the iterate_devices
> loop in dm_table_supports_write_same() should return false.
>
> Reported-by: Bharata B Rao <bharata.rao@gmail.com>
> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> Cc: stable@vger.kernel.org # v3.8+
> ---
>  drivers/md/dm-table.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 3fe797f..d801682 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -1445,7 +1445,7 @@ static bool dm_table_supports_write_same(struct dm_table *t)
>                         return false;
>
>                 if (!ti->type->iterate_devices ||
> -                   !ti->type->iterate_devices(ti, device_not_write_same_capable, NULL))
> +                   ti->type->iterate_devices(ti, device_not_write_same_capable, NULL))
>                         return false;
>         }
>
> --
> 1.7.1
>



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[PATCH] dm mpath: enable WRITE SAME support

[Mike Snitzer]

On Wed, May 01 2013 at  2:58am -0400,
Bharata B Rao <bharata.rao@gmail.com> wrote:

> On Tue, Apr 30, 2013 at 10:02 PM, Mike Snitzer <snitzer@redhat.com> wrote:
> > On Tue, Apr 30 2013 at 12:07am -0400,
> > Bharata B Rao <bharata.rao@gmail.com> wrote:
> >
> >>
> >> # lsblk
> >> NAME                             MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
> >> sda                                8:0    0    50G  0 disk
> >> └─mpathb (dm-12)                 252:12   0    50G  0 mpath
> >>   └─ws_vg-lvol0 (dm-11)          252:11   0     1G  0 lvm
> >> sde                                8:64   0    50G  0 disk
> >> └─mpathb (dm-12)                 252:12   0    50G  0 mpath
> >>   └─ws_vg-lvol0 (dm-11)          252:11   0     1G  0 lvm
> >>
> >
> >
> > Anyway, this patch fixes things for me:
> 
> Thanks, this fixes the issue for me too. However if LV/VG/PV are
> created on multipath device, then WRITE SAME still doesn't get
> advertised for the LV. I had to disable multipath and re-create
> LV/VG/PV on a normal device (/dev/sda as against /dev/mapper/mapathb)
> to get BLKZEROUT working on LV.

The multipath target did not opt-in to supporting WRITE SAME.  Please
try this patch.

From: Mike Snitzer <snitzer@redhat.com>
Subject: [PATCH] dm mpath: enable WRITE SAME support

There is no reason to disallow WRITE SAME support.  As far as multipath
is concerned it is just another write request.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 drivers/md/dm-mpath.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 51bb816..bdf26f5 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -907,6 +907,7 @@ static int multipath_ctr(struct dm_target *ti, unsigned int argc,
 
 	ti->num_flush_bios = 1;
 	ti->num_discard_bios = 1;
+	ti->num_write_same_bios = 1;
 
 	return 0;
 
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Re: [PATCH] dm mpath: enable WRITE SAME support

[Bharata B Rao]

On Wed, May 1, 2013 at 6:59 PM, Mike Snitzer <snitzer@redhat.com> wrote:
>
> The multipath target did not opt-in to supporting WRITE SAME.  Please
> try this patch.
>
> From: Mike Snitzer <snitzer@redhat.com>
> Subject: [PATCH] dm mpath: enable WRITE SAME support
>
> There is no reason to disallow WRITE SAME support.  As far as multipath
> is concerned it is just another write request.
>
> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> ---
>  drivers/md/dm-mpath.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> index 51bb816..bdf26f5 100644
> --- a/drivers/md/dm-mpath.c
> +++ b/drivers/md/dm-mpath.c
> @@ -907,6 +907,7 @@ static int multipath_ctr(struct dm_target *ti, unsigned int argc,
>
>         ti->num_flush_bios = 1;
>         ti->num_discard_bios = 1;
> +       ti->num_write_same_bios = 1;

With this patch, I can see the LV that is on multipath device,
advertising the WRITE SAME support and I am able to successfully issue
BLKZEROOUT ioctl to that LV.

Regards,
Bharata.