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563e584da4
It turns out I've been using pthread_setname_np wrong the whole time: * on Linux, the thread name length is 15 characters. TASK_COMM_LEN is 16 bytes, and the last one is always 0. This is now hardcoded in many places and cannot be changed. * pthread_setname_np doesn't return -errno, so DIE_IF_MINUS_ERRNO was the wrong macro. On the other hand, we never want to do anything differently when pthread_setname_np fails, so we never needed to check the return value. Also, libc silently ignores attempts to set the thread name when it is too long. That's almost certainly a libc bug, but libc probably suppresses the error result for the same reasons I ignore the error result. Wrap the pthread_setname function with a C++ std::string overload that truncates the argument at 15 characters, so we at least get the first part of the task name in the thread name field. Later commits can deal with making the bees thread names shorter. Also wrap pthread_getname for symmetry. 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)
- Daemon incrementally dedupes new data using btrfs tree search
- Works with btrfs compression - dedupe any combination of compressed and uncompressed files
- NEW Works around
btrfs sendproblems with dedupe and incremental parent snapshots - 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
- 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
- bees Gotchas
- btrfs kernel bugs - especially DATA CORRUPTION WARNING
- bees vs. other btrfs features
- What to do when something goes wrong
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 2015-2022 Zygo Blaxell bees@furryterror.org.
GPL (version 3 or later).