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 <[email protected]> > CC: Kevin Wolf <[email protected]> > CC: Max Reitz <[email protected]> > CC: Eduardo Habkost <[email protected]> > CC: Marcel Apfelbaum <[email protected]> > CC: John Snow <[email protected]> > CC: Paolo Bonzini <[email protected]> > CC: Fam Zheng <[email protected]> > > ping v3
