Re: [Qemu-devel] TRIM/DISCARD/UNMAP support on qemu-nbd

[Paolo Bonzini]

Il 07/01/2014 22:22, Richard W.M. Jones ha scritto:
> On Tue, Jan 07, 2014 at 09:48:17PM +0100, Paolo Bonzini wrote:
>> Il 07/01/2014 21:27, Richard W.M. Jones ha scritto:
>>> Not much more what I said in the original email (especially see the
>>> attached script which you can download from the bottom of this page:
>>> https://lists.gnu.org/archive/html/qemu-devel/2014-01/msg00084.html )
>>>
>>> Basically it tries to dd /dev/zero into the virtio-scsi device exposed
>>> by qemu, then calls sg_unmap (there are two devices, it only unmaps
>>> the first so we can hopefully see the difference), but it doesn't seem
>>> to have any effect on the underlying file.  The underlying file is a
>>> regular raw-format file on ext4.
>>>
>>> I called sg_readcap/sg_vpd and we seem to have all the right
>>> capability bits exposed.
>>>
>>> This script won't work with regular libguestfs.  I compiled a special
>>> appliance that had the sg tools included.
>>
>> Try again with the pull request of
>> http://permalink.gmane.org/gmane.comp.emulators.qemu/248421
> 
> No difference from before, as far as I can see.
> 
> Here is the output of sparsetest.sh:

Is guestfish using "discard=on"?  Here is my test:

$ qemu-img create test.img 32M
Formatting 'test.img', fmt=raw size=33554432
$ qemu-img map --output=json test.img
[{ "start": 0, "length": 33554432, "depth": 0, "zero": true, "data":
false, "offset": 0}]
$ qemu-system-x86_64 ~/rhel6.img \
  -drive if=none,cache=none,discard=on,file=test.img,id=test \
  -device virtio-scsi-pci -device scsi-disk,drive=test \
  --enable-kvm -m 512

  ========
  In guest
  ========

  # sg_readcap /dev/sdb
  Device size: 33554432 bytes, 32.0 MiB, 0.03 GB
  # cat /sys/block/sdb/device/scsi_disk/*/provisioning_mode
  unmap
  # yes | mkfs.ext4 /dev/sdb
  # mount /dev/sdb test
  # dd if=/dev/zero of=test/test bs=1M

$ du -sh test.img
32M     test.img

  ========
  In guest
  ========

  # rm xfs/test
  (sync here if it does not work)
  # fstrim -v xfs/
  xfs/: 27891712 bytes were trimmed

$ du -sh test.img
5.2M    test.img