Am 27.07.2018 um 05:33 hat Fam Zheng geschrieben: > Kevin pointed out that both glibc and kernel provides a slow fallback of > copy_file_range which hurts thin provisioning. This is particularly true for > thin LVs, because host_device driver cannot get allocation info from the > volume, and copy_file_range is called on every sectors, making the dst fully > allocated. > > NFS mount points also doesn't support SEEK_DATA well, so the allocation > information is unknown to QEMU. > > That leaves only iscsi:// which seems to do what we want so far, but it is a > smaller use case. > > Add an option to qemu-img convert, "-C", to enable (attempting) copy > offloading > explicitly. And mark it incompatible with "-S" and "-c".
Reviewed-by: Kevin Wolf <kw...@redhat.com> Not sure why you made this an RFC only, but I think we absolutely need this. People are used to using 'qemu-img convert' to compact images and this would regress with automatic copy offloading. Do you think we need more discussion? Kevin
