** Changed in: linux (Ubuntu Disco)
Status: New => Fix Committed
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https://bugs.launchpad.net/bugs/1841977
Title:
shiftfs: drop entries from cache on unlink
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Disco:
Fix Committed
Bug description:
SRU Justification
Impact: LXD on Ubuntu runs on top of zfs by defaults. Users that make use of
shiftfs for efficient id-shifting currently hit a bug where zfs is confused
about the amount of space that is used in a dataset. For example, creating a
file with 1GB of random data will increase the space used by the dataset by
1GB. When the file is removed via rm the space is not freed for zfs. This leads
to zfs running out of space pretty quickly.
This bug has been observed, described, and reproduced here
https://discuss.linuxcontainers.org/t/trying-out-shiftfs/5155/9 . Stéphane
Graber observed related issues.
Regression Potential: Limited to shiftfs. This patch has been tested
on various backends btrfs, dir, zfs to verify that it doesn't regress
other workloads. Shiftfs now also aligns more closely with overlayfs
on file deletion.
Test Case:
sudo snap install lxd
sudo snap set lxd shiftfs.enable=true
sudo systemctl restart snap.lxd.daemon
sudo lxd init # make sure to select zfs as backend
sudo lxc launch images:ubuntu/bionic b1
sudo lxc exec b1 -- dd if=/dev/urandom bs=1M count=1000 of=dummy.file
sudo zfs list default/containers/b1 # will show +1GB
sudo lxc exec b1 -- rm dummy.file
sudo zfs list default/containers/b1 # will show +1GB on a non-fixed kernel
and -1GB on a fixed kernel
Target Kernels: All LTS kernels with shiftfs support.
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