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LOGICAL_INO can trip over the btrfs slow-backrefs bug, resulting in some very long in-kernel runtimes. If too many threads are executing LOGICAL_INO then there may be no cores left on the system to run other tasks. Toxic extent detection is done by a very rudimentary algorithm which can be confused by unrelated sources of latency within btrfs (especially commit latency). The algorithm can also be confused by other threads executing the LOGICAL_INO ioctl. These are two good reasons to prevent any two threads in a single bees process instance from executing LOGICAL_INO at the same time, so let's do that. It is possible to limit the number of threads executing LOGICAL_INO with the -c and -C options; however, this also limits the number of threads which can perform any operation, while only LOGICAL_INO (*) has such a profound effect on the rest of system operation. Also make the status message clearer about exactly when LOGICAL_INO is executed, as opposed to merely waiting to acquire a lock before executing the ioctl. (*) or maybe FILE_EXTENT_SAME. The problem function that keeps showing up in kernel stack traces is find_parent_nodes, which is called by both the LOGICAL_INO and FILE_EXTENT_SAME ioctls. We'll try this change first and see if it prevents any recurrences of forced watchdog reboots; if it does not, then we'll limit FILE_EXTENT_SAME the same way. Signed-off-by: Zygo Blaxell <bees@furryterror.org>
BEES
Best-Effort Extent-Same, a btrfs deduplication agent.
About bees
bees is a block-oriented userspace deduplication agent designed for large btrfs filesystems. It is an offline dedupe combined with an incremental data scan capability to minimize time data spends on disk from write to dedupe.
Strengths
- Space-efficient hash table and matching algorithms - can use as little as 1 GB hash table per 10 TB unique data (0.1GB/TB)
- Incremental realtime dedupe of new data using btrfs tree search
- Works with btrfs compression - dedupe any combination of compressed and uncompressed files
- Works around btrfs filesystem structure to free more disk space
- Persistent hash table for rapid restart after shutdown
- Whole-filesystem dedupe - including snapshots
- Constant hash table size - no increased RAM usage if data set becomes larger
- Works on live data - no scheduled downtime required
- Automatic self-throttling based on system load
Weaknesses
- Whole-filesystem dedupe - has no include/exclude filters, does not accept file lists
- Runs continuously as a daemon - no quick start/stop
- Requires root privilege (or
CAP_SYS_ADMIN) - First run may require temporary disk space for extent reorganization
- First run may increase metadata space usage if many snapshots exist
- Constant hash table size - no decreased RAM usage if data set becomes smaller
- btrfs only
Installation and Usage
Recommended Reading
More Information
Bug Reports and Contributions
Email bug reports and patches to Zygo Blaxell bees@furryterror.org.
You can also use Github:
https://github.com/Zygo/bees
Copyright & License
Copyright 2015-2018 Zygo Blaxell bees@furryterror.org.
GPL (version 3 or later).