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Gao Xiang e96ebc0085 erofs-snapshotter: make IMMUTABLE_FL optional

Enabling the IMMUTABLE_FL file attribute causes dirty data to be
flushed synchronously at least on EXT4, which can greatly impact
container launch performance.  In contrast, the overlayfs snapshotter
does not use syncfs by default.

Most users may not need IMMUTABLE_FL, let's make IMMUTABLE_FL optional
to align with the behavior of the overlayfs snapshotter and recover the
original performance.

1. tensorflow

Test commands:
$ nerdctl image pull --snapshotter=X --unpack="false" tensorflow/tensorflow:2.19.0
$ time nerdctl container --snapshotter=X run -d tensorflow/tensorflow:2.19.0 /bin/sh

Results:
 overlayfs                 | 0m18.748s
 erofs (no IMMUTABLE_FL)   | 0m10.090s
 erofs (with IMMUTABLE_FL) | 0m21.074s

2. ubuntu 22.04

Test commands:
$ nerdctl image pull --snapshotter=X --unpack="false" ubuntu:22.04
$ time nerdctl container --snapshotter=X run -d ubuntu:22.04 /bin/sh

Results:
 overlayfs                 | 0m1.147s
 erofs (no IMMUTABLE_FL)   | 0m0.795s
 erofs (with IMMUTABLE_FL) | 0m1.094s

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

2025-07-11 02:56:37 +08:00

blockfile.md

document usage and design of blockfile snapshotter

2024-04-28 11:44:03 +03:00

devmapper.md

update some devmapper docs

2022-07-11 15:49:54 +00:00

erofs.md

erofs-snapshotter: make IMMUTABLE_FL optional

2025-07-11 02:56:37 +08:00

README.md

Add EROFS snapshotter documentation

2025-01-13 16:31:21 +08:00

README.md

Snapshotters

Snapshotters manage the snapshots of the container filesystems.

The available snapshotters can be inspected by running ctr plugins ls or nerdctl info.

Core snapshotter plugins

Generic:

overlayfs (default): OverlayFS. This driver is akin to Docker/Moby's "overlay2" storage driver, but containerd's implementation is not called "overlay2".
native: Native file copying driver. Akin to Docker/Moby's "vfs" driver.

Block-based:

blockfile: A driver using raw block files for each snapshot. Block files are copied from a parent or base empty block file. Mounting requires a virtual machine or support for loopback mounts.
devmapper: ext4/xfs device mapper. See devmapper.md.

Filesystem-specific:

btrfs: btrfs. Needs the plugin root (/var/lib/containerd/io.containerd.snapshotter.v1.btrfs) to be mounted as btrfs.
zfs: ZFS. Needs the plugin root (/var/lib/containerd/io.containerd.snapshotter.v1.zfs) to be mounted as ZFS. See also https://github.com/containerd/zfs .
erofs: EROFS. OverlayFS kernel module needs to be enabled for active snapshots. See also erofs.md.

Deprecated:

aufs: AUFS. Deprecated since containerd 1.5. Removed in containerd 2.0. See also https://github.com/containerd/aufs .

Non-core snapshotter plugins

fuse-overlayfs: FUSE-OverlayFS Snapshotter
nydus: Nydus Snapshotter
overlaybd: OverlayBD Snapshotter
stargz: Stargz Snapshotter

Mount target

Mounts can optionally specify a target to describe submounts in the container's rootfs. For example, if the snapshotter wishes to bind mount to a subdirectory ontop of an overlayfs mount, they can return the following mounts:

[
    {
        "type": "overlay",
        "source": "overlay",
        "options": [
            "workdir=...",
            "upperdir=...",
            "lowerdir=..."
        ]
    },
    {
        "type": "bind",
        "source": "/path/on/host",
        "target": "/path/inside/container",
        "options": [
            "ro",
            "rbind"
        ]
    }
]

However, the mountpoint /path/inside/container needs to exist for the bind mount, so one of the previous mounts must be responsible for providing that directory in the rootfs. In this case, one of the lower dirs of the overlay has that directory to enable the bind mount.