On Sun, Jun 28, 2020 at 8:11 AM Fabio Valentini <decathorpe@xxxxxxxxx> wrote: > > From what I remember about Android Studio / Simulator, it uses qemu and disk images under the hood. Setting the nodatacow attribute (chattr +C, I think?) on VM images should improve performance by a fair bit. chattr +C (nodatacow) is recommended. - no limitation on snapshotting - limitation on reflink copies. cp --reflink is permitted between locations with the same cow attribute, i.e. if the file has +C then the destination dir needs +C; otherwise --reflink=always will fail and --reflink=auto will fall back to monolithic copy of the whole image. - implies no compression and no data checksums. There might be narrow use cases where it's preferred to retain datacow behavior. i.e. I think it's fine for nodatacow to be the default, the question is whether and how easy to opt out. > Maybe libvirt / gnome-boxes / virt-manager should do that by default if it detects that the backing storage for an allocated VM image is on btrfs (if it doesn't do that already)? Yes. There are many possibilities. It can be done at file create time (qemu-img already has an option that causes +C attribute to be set). Maybe the installer could set it on the containing directory; or likewise libvirtd could do it. systemd-journald for a while now detects if /var/log/journal is on btrfs and automatically sets +C attribute, so it could be something similar for libvirtd, and use a drop in empty file to inhibit? sd-journald uses /etc/tmpfiles.d/journal-nocow.conf to inhibit. -- Chris Murphy _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx
