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Recently scoutfs_alloc_move() was changed to try and limit the amount of metadata blocks it could allocate or free. The intent was to stop concurrent holders of a transaction from fully consuming the available allocator for the transaction. The limiting logic was a bit off. It stopped when the allocator had the caller's limit remaining, not when it had consumed the caller's limit. This is overly permissive and could still allow concurrent callers to consume the allocator. It was also triggering warning messages when a call consumed more than its allowed budget while holding a transaction. Unfortunately, we don't have per-caller tracking of allocator resource consumption. The best we can do is sample the allocators as we start and return if they drop by the caller's limit. This is overly conservative in that it accounts any consumption during concurrent callers to all callers. This isn't perfect but it makes the failure case less likely and the impact shouldn't be significant. We don't often have a lot of concurrency and the limits are larger than callers will typically consume. 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
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