On Mon, Sep 20 2010 at 1:40pm -0400,
Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> Hi Ted,
>
> On Mon, Sep 20 2010 at 9:14am -0400,
> Theodore Ts'o <tytso@xxxxxxx> wrote:
>
> > Hi there,
> >
> > I was just testing discard support in mke2fs, and I was surprised that
> > although the dm layer appears to pass discard requests through to the
> > underlying block device driver when submitted through the bio layer
> > (i.e., from kernel file systems), apparently the discard ioctls (i.e.,
> > BLKDISCARD, BLKDISCARDSEC, BLKDISCARDZEROES) are not currently wired up
> > in the dm layer.
>
> After enabling scsi tracing:
> # mount -t debugfs none /sys/kernel/debug
> # cd /sys/kernel/debug/tracing/
> # echo "scsi:*" > set_event
> # cat trace_pipe
>
> I'm not seeing a problem with BLKDISCARD (via mkfs.ext4) for either
> request-based DM (this is on a 2.6.36-rc4 kernel w/ the FLUSH+FUA patchset):
Here is a trace during mkfs.ext4 of a bio-based striped DM device (with
4 stripes) on a stock 2.6.36-rc4:
mkfs.ext4-3835 [000] 6050624.201765: scsi_dispatch_cmd_start: host_no=10 channel=0 id=0 lun=0 data_sgl=1 prot_sgl=0 cmnd=(UNMAP regions=1 raw=42 00 00 00 00 00 00 00 18 00)
mkfs.ext4-3835 [000] 6050624.201790: scsi_dispatch_cmd_start: host_no=10 channel=0 id=0 lun=0 data_sgl=1 prot_sgl=0 cmnd=(UNMAP regions=1 raw=42 00 00 00 00 00 00 00 18 00)
mkfs.ext4-3835 [000] 6050624.201806: scsi_dispatch_cmd_start: host_no=10 channel=0 id=0 lun=0 data_sgl=1 prot_sgl=0 cmnd=(UNMAP regions=1 raw=42 00 00 00 00 00 00 00 18 00)
mkfs.ext4-3835 [000] 6050624.201823: scsi_dispatch_cmd_start: host_no=10 channel=0 id=0 lun=0 data_sgl=1 prot_sgl=0 cmnd=(UNMAP regions=1 raw=42 00 00 00 00 00 00 00 18 00)
<idle>-0 [000] 6050624.202772: scsi_dispatch_cmd_done: host_no=10 channel=0 id=0 lun=0 data_sgl=1 prot_sgl=0 cmnd=(UNMAP regions=1 raw=42 00 00 00 00 00 00 00 18 00) result=(driver=DRIVER_OK host=DID_OK message=COMMAND_COMPLETE status=SAM_STAT_GOOD)
<idle>-0 [000] 6050624.202774: scsi_dispatch_cmd_done: host_no=10 channel=0 id=0 lun=0 data_sgl=1 prot_sgl=0 cmnd=(UNMAP regions=1 raw=42 00 00 00 00 00 00 00 18 00) result=(driver=DRIVER_OK host=DID_OK message=COMMAND_COMPLETE status=SAM_STAT_GOOD)
<idle>-0 [000] 6050624.202775: scsi_dispatch_cmd_done: host_no=10 channel=0 id=0 lun=0 data_sgl=1 prot_sgl=0 cmnd=(UNMAP regions=1 raw=42 00 00 00 00 00 00 00 18 00) result=(driver=DRIVER_OK host=DID_OK message=COMMAND_COMPLETE status=SAM_STAT_GOOD)
<idle>-0 [000] 6050624.202775: scsi_dispatch_cmd_done: host_no=10 channel=0 id=0 lun=0 data_sgl=1 prot_sgl=0 cmnd=(UNMAP regions=1 raw=42 00 00 00 00 00 00 00 18 00) result=(driver=DRIVER_OK host=DID_OK message=COMMAND_COMPLETE status=SAM_STAT_GOOD)
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