Re: pls consider this is [v3] Re: [PATCH 0/2] block: propagate discard alignment from format drivers to the guest

[Denis V. Lunev]

On 6/11/20 8:21 PM, Denis V. Lunev wrote:
> On 6/11/20 8:16 PM, Denis V. Lunev wrote:
>> Nowaday SCSI drivers in guests are able to align UNMAP requests before
>> sending to the device. Right now QEMU provides an ability to set
>> this via "discard_granularity" property of the block device which could
>> be used by management layer.
>>
>> Though, in particular, from the point of QEMU, there is
>> pdiscard_granularity on the format driver level, f.e. on QCOW2 or iSCSI.
>> It would be beneficial to pass this value as a default for this
>> property.
>>
>> Technically this should reduce the amount of use less UNMAP requests
>> from the guest to the host. Basic test confirms this. Fedora 31 guest
>> during 'fstrim /' on 32 Gb disk has issued 401/415 requests with/without
>> proper alignment to QEMU.
>>
>> Changes from v2:
>> - 172 iotest fixed
>>
>> Changes from v1:
>> - fixed typos in description
>> - added machine type compatibility layer as suggested by Kevin
>>
>> Signed-off-by: Denis V. Lunev <den@openvz.org>
>> CC: Kevin Wolf <kwolf@redhat.com>
>> CC: Max Reitz <mreitz@redhat.com>
>> CC: Eduardo Habkost <ehabkost@redhat.com>
>> CC: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
>> CC: John Snow <jsnow@redhat.com>
>> CC: Paolo Bonzini <pbonzini@redhat.com>
>> CC: Fam Zheng <fam@euphon.net>
>>
>>
> Sorry for missed v3 tag in the subject :(
ping