On Sun, Jun 28, 2020 at 8:11 AM Fabio Valentini <decatho...@gmail.com> 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@lists.fedoraproject.org To unsubscribe send an email to devel-le...@lists.fedoraproject.org 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@lists.fedoraproject.org
