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Date: Mon, 10 Mar 2014 17:57:01 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] Trying to get fstrim / discard=unmap to work
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To: "Richard W.M. Jones" <rjones@redhat.com>, qemu-devel@nongnu.org

Il 10/03/2014 17:14, Richard W.M. Jones ha scritto:
> On Mon, Mar 10, 2014 at 04:11:20PM +0000, Richard W.M. Jones wrote:
>> Guest:
>>  - guest kernel: 3.13.4-200.fc20.x86_64
>>  - ext4 guest filesystem
>>  - fstrim from util-linux 2.24.1
>>  - cat /sys/block/sda/device/scsi_disk/*/provisioning_mode
>>    unmap
>
> I noticed that I wasn't mounting the guest filesystem with '-o discard'.
> However it still doesn't work even after adding this option.

Works here:

$ qemu-system-x86_64 -drive 
discard=unmap,file=$HOME/jeos-19-64.qcow2,id=ff,if=none -device 
virtio-scsi-pci -device scsi-disk,drive=ff -vnc :0 --enable-kvm

Before test:
$ du -h jeos-19-64.qcow2
1,6G	jeos-19-64.qcow2

After "dd if=/dev/zero of=foo bs=1M count=300":
$ du -h jeos-19-64.qcow2
1,8G	jeos-19-64.qcow2

After "rm foo; fstrim -v /":
$ du -h jeos-19-64.qcow2
1,4G	jeos-19-64.qcow2

I also set a breakpoint on fallocate64, and it was called.

Paolo