XCG: Decoupling Control from Configuration to Improve Cgroup Scalability with Flat Mapping

This repository contains the open-source release of XCG, an extension to the Linux cgroup v2 framework that improves cgroup scalability for serverless container startup. It is the implementation accompanying the paper:

Ruofan Xiong, Li Wang, Zhihao Zhang, Xinbiao Gan, and Yiming Zhang. XCG: Decoupling Control from Configuration to Improve Cgroup Scalability with Flat Mapping. SIGOPS ATC 2026. https://doi.org/10.1145/3828523.3857116

XCG implements, on Linux kernel v6.7.2.

Repository contents

patches/
  0001-xcg-core.patch                  cgroup core: ioctl dispatch, XCG domains,
                                       flat mapping, async-create framework,
                                       deferred destroy, UAPI header, README
  0002-xcg-cpu-controller.patch      CPU controller: async create, lazy per-CPU
                                       cfs_rq/se, tg recycle, hotplug prewarm
  0003-xcg-memory-controller.patch   memory controller: async create, lazy
                                       per-NUMA nodeinfo, memcg recycle
  0004-xcg-pids-cpuset-controllers.patch  pids + cpuset: async create, lazy
                                       per-CPU counter / effective masks,
                                       recycle lists
  0005-xcg-io-controller.patch       io (blkcg): async create, lazy per-policy
                                       cpd[] + per-CPU lhead, recycle list
  0006-xcg-selftests.patch           26 kselftests (test_xcg_*) + xcg_helpers.h
                                       under tools/testing/selftests/cgroup/

The patches carry a series file for quilt; they also apply cleanly in number order with git apply or patch -p1.

Applying

Starting from a pristine Linux v6.7.2 tree (https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.7.2.tar.xz):

cd linux-6.7.2
for p in /path/to/this/repo/patches/*.patch; do
    patch -p1 < "$p"
done

(or git apply each patch in order inside a git checkout of v6.7.2.)

Building

XCG is controlled by CONFIG_CGROUP_XCG (bool, default y, depends on CGROUPS):

make defconfig
make -j$(nproc)
sudo make modules_install install

Boot the patched kernel with cgroup v2 mounted.

Testing

The patched tree ships kselftests under tools/testing/selftests/cgroup/. On a machine (a VM is recommended) booted into the patched kernel:

make -C tools/testing/selftests/cgroup
cd tools/testing/selftests/cgroup
echo "+cpu +memory +pids +cpuset +io" | \
    sudo tee /sys/fs/cgroup/cgroup.subtree_control
sudo ./test_xcg_errors       
sudo ./test_xcg_mkdir        
sudo ./test_xcg_set           
sudo ./test_xcg_stat          
sudo ./test_xcg_attach        
sudo ./test_xcg_migrate     
sudo ./test_xcg_async         
sudo ./test_xcg_async_recycle 
sudo ./test_xcg_memcg_async   
sudo ./test_xcg_pids_async   
sudo ./test_xcg_cpuset_async  
sudo ./test_xcg_io_async      
sudo ./test_xcg_domain       
sudo ./test_xcg_hierarchy     
sudo ./test_xcg_destroy_fast 
sudo ./test_core             
sudo ./test_memcontrol       

See the in-tree README after applying for the full design/code map.

License

The patches are licensed under the same terms as the Linux kernel: GPL-2.0 (see COPYING in the kernel tree); the UAPI header include/uapi/linux/xcg.h is GPL-2.0 WITH Linux-syscall-note. Individual files carry SPDX identifiers.