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The block cache had a bizarre cache eviction policy that was trying to avoid precise LRU updates at each block. It had pretty bad behaviour, including only allowing reclaim of maybe 20% of the blocks that were visited by the shrinker. We can use the existing list_lru facility in the kernel to do a better job. Blocks only exhibit contention as they're allocated and added to per-node lists. From then on we only set accessed bits and the private list walkers move blocks around on the list as we see the accessed bits. (It looks more like a fifo with lazy promotion than a "LRU" that is actively moving list items around as they're accessed.) Using the facility means changing how we remove blocks from the cache and hide them from lookup. We clean up the refcount inserted flag a bit to be expressed more as a base refcount that can be acquired by whoever's removing from the cache. It seems a lot clearer. Signed-off-by: Zach Brown <zab@versity.com>
Introduction
scoutfs is a clustered in-kernel Linux filesystem designed to support large archival systems. It features additional interfaces and metadata so that archive agents can perform their maintenance workflows without walking all the files in the namespace. Its cluster support lets deployments add nodes to satisfy archival tier bandwidth targets.
The design goal is to reach file populations in the trillions, with the archival bandwidth to match, while remaining operational and responsive.
Highlights of the design and implementation include:
- Fully consistent POSIX semantics between nodes
- Atomic transactions to maintain consistent persistent structures
- Integrated archival metadata replaces syncing to external databases
- Dynamic seperation of resources lets nodes write in parallel
- 64bit throughout; no limits on file or directory sizes or counts
- Open GPLv2 implementation
Community Mailing List
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