On Fri, Sep 02, 2016 at 09:36:31PM -0600, Chris Murphy wrote:
On Fri, Sep 2, 2016 at 8:17 PM, Jeff Mahoney <jeffm@suse.com> wrote:
Qgroups are enabled to allow snapper to make better decisions about which snapshots to remove automatically. To do this, we only need the qgroups tracking data. We do *nothing* with automatically adding or enforcing limits using them. In a later post, Chris claims that snapper doesn't do this and in fact uses FIEMAP and INO_LOOKUP.
No, that was in response to Andrei about what 'btrfs filesystem du' is using, not snapper.
The implicit question is why snapper can't use the same ioctl 'fi du' is using, instead of qgroups.
snapper could use 'fi du' concept but it does not due for performance. Without quota groups snapper would have to iterate through every snapshot (that is a candidate to be deleted) and lookup every file, lookup backrefs and alike. Just compare the time of e.g. 'btrfs quota rescan -w / ; btrfs qgroup show -p /' and 'btrfs filesystem du -s /.snapshots/*' to get a feeling for the difference. On my test system (virtual machine with small installation and only 10 snapshots) it is 2 seconds vs. 3 minutes (with hot caches). Regards, Arvin -- Arvin Schnell, <aschnell@suse.com> Senior Software Engineer, Research & Development SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) Maxfeldstraße 5 90409 Nürnberg Germany -- To unsubscribe, e-mail: opensuse-factory+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-factory+owner@opensuse.org