e2c84bfba7
The PIE restorer cannot link against LZ4. Decode mappings containing LZ4 payloads through CRIU's premap path, while retaining delayed PIE restore for raw and zero ranges when a worker pool cannot help. Classify image ranges as LZ4, raw, or zero. Decode LZ4 blocks while CRIU still runs in its normal address space, read aligned raw ranges directly into their final VMAs, and clear zero ranges in place. Omit compression metadata for entries containing only raw blocks so they retain the ordinary restore path. Share one encoded-read context across each incremental parent chain and reuse its worker pool for bounded batches, COW reads, streamed images, and page-server chunks. Use the same jobs to fill zero runs of at least 1 MiB when two blocks and two CPUs are available. Zero-only ranges that cannot benefit retain the PIE path, while zero blocks in an existing encoded batch remain inline without effective parallel capacity. Hold input buffers only while encoded work is active, and join every worker before child restore or the PIE handoff. Account calling restore threads and workers against a shared CPU budget. A requested width of zero selects automatic concurrency, one keeps LZ4 decoding serial and disables zero-fill workers, and larger values cap aggregate worker concurrency. Bound the active width by CPU affinity and useful work. Release encoded-work leases before ordinary reads so idle contexts cannot block ready workers. Local payload-heavy restores otherwise alternate between reading an encoded batch and decoding it. This leaves either storage or worker CPUs idle. When a second encoded-input lease is immediately available, dispatch the current batch to the pool and use the already-accounted calling thread to read the next adjacent payload. Keep synchronous reads for serial restore, streams, direct I/O, small batches, and contended leases. Select direct AIO from the ranges actually delayed for PIE. Batch inherited COW comparisons and streamed payload reads, and align page-server chunks to compression regions. Validate metadata and offset arithmetic before allocation or I/O, roll back partially enqueued work, and propagate worker, I/O, and deferred deduplication failures before remapping. On a 256 MiB pseudorandom workload with the worker limit set to eight and three measured runs, median restore time was 114.5 ms uncompressed, 113.4 ms with LZ4 per page, and 116.5 ms with 64 KiB regions. The previous compressed restore path took about 227 ms in either mode. With automatic concurrency and 256 KiB regions, parallel zero filling reduced median restore time over five runs from 103.1 ms to 31.7 ms for zero-filled memory and from 89.3 ms to 60.0 ms for mixed memory. On 512 MiB TEXT and ELF workloads with automatic concurrency and 256 KiB regions, five-run median restore time fell from 117.0 ms to 110.7 ms and from 115.4 ms to 109.5 ms, respectively. Assisted-by: Codex:GPT-5 Assisted-by: Claude:claude-fable-5 Signed-off-by: Radostin Stoyanov <rstoyanov@fedoraproject.org> |
||
|---|---|---|
| .circleci | ||
| .github | ||
| compel | ||
| contrib | ||
| coredump | ||
| crit | ||
| criu | ||
| Documentation | ||
| images | ||
| include | ||
| lib | ||
| plugins | ||
| scripts | ||
| soccr | ||
| test | ||
| .clang-format | ||
| .codespellrc | ||
| .gitignore | ||
| .lgtm.yml | ||
| .mailmap | ||
| CLAUDE.md | ||
| CONTRIBUTING.md | ||
| COPYING | ||
| CREDITS | ||
| docs | ||
| flake.lock | ||
| flake.nix | ||
| GEMINI.md | ||
| INSTALL.md | ||
| MAINTAINERS | ||
| MAINTAINERS_GUIDE.md | ||
| Makefile | ||
| Makefile.compel | ||
| Makefile.config | ||
| Makefile.install | ||
| Makefile.versions | ||
| README.md | ||
CRIU -- A project to implement checkpoint/restore functionality for Linux
CRIU (stands for Checkpoint and Restore in Userspace) is a utility to checkpoint/restore Linux tasks.
Using this tool, you can freeze a running application (or part of it) and checkpoint it to a hard drive as a collection of files. You can then use the files to restore and run the application from the point it was frozen at. The distinctive feature of the CRIU project is that it is mainly implemented in user space. There are some more projects doing C/R for Linux, and so far CRIU appears to be the most feature-rich and up-to-date with the kernel.
CRIU project is (almost) the never-ending story, because we have to always keep up with the Linux kernel supporting checkpoint and restore for all the features it provides. Thus we're looking for contributors of all kinds -- feedback, bug reports, testing, coding, writing, etc. Please refer to CONTRIBUTING.md if you would like to get involved.
The project started as the way to do live migration for OpenVZ Linux containers, but later grew to more sophisticated and flexible tool. It is currently used by (integrated into) OpenVZ, LXC/LXD, Docker, and other software, project gets tremendous help from the community, and its packages are included into many Linux distributions.
The project home is at http://criu.org. This wiki contains all the knowledge base for CRIU we have. Pages worth starting with are:
- Installation instructions
- A simple example of usage
- Examples of more advanced usage
- Troubleshooting can be hard, some help can be found here, here and here
Checkpoint and restore of simple loop process
Advanced features
As main usage for CRIU is live migration, there's a library for it called P.Haul. Also the project exposes two cool core features as standalone libraries. These are libcompel for parasite code injection and libsoccr for TCP connections checkpoint-restore.
Live migration
True live migration using CRIU is possible, but doing all the steps by hands might be complicated. The phaul sub-project provides a Go library that encapsulates most of the complexity. This library and the Go bindings for CRIU are stored in the go-criu repository.
Parasite code injection
In order to get state of the running process CRIU needs to make this process execute some code, that would fetch the required information. To make this happen without killing the application itself, CRIU uses the parasite code injection technique, which is also available as a standalone library called libcompel.
TCP sockets checkpoint-restore
One of the CRIU features is the ability to save and restore state of a TCP socket without breaking the connection. This functionality is considered to be useful by itself, and we have it available as the libsoccr library.
Licence
The project is licensed under GPLv2 (though files sitting in the lib/ directory are LGPLv2.1).
All files in the images/ directory are licensed under the Expat license (so-called MIT). See the images/LICENSE file.