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The first pass at managing the cluster lock state machine used a simple global spinlock. It's time to break it up. This adds refcounting to the cluster lock struct. Rather than managing global data structures and individual lock state all under a global spinlock, we use per-structure locks, a lock spinlock, and a lock refcount. Active users of the cluster lock hold a reference. This primarily lets unlock only check global structures once the refcounts say that it's time to remove the lock from the structures. The careful use of the refcount to avoid locks that are being freed during lookup also paves the way for using mostly read-only RCU lookup structures soon. The global LRU is still modified on every lock use, that'll also be removed up in future work. The linfo spinlock is now only used for the LRU and lookup structures. Other uses are removed, which causes more careful use of the finer grained locks that initially just mirrored the use of the linfo spinlock to keep those introduction patches safe. The move from a single global lock to more fine grained locks creates nesting that needs to be managed. Shrinking and recovery in particular need to be careful as they transition from spinlocks used to find cluster locks to getting the cluster lock spinlock. The presence of freeing locks in the lookup indexes means that some callers need to retry if they hit freeing locks. We have to add this protection to recovery iterating over locks by their key value, but it wouldn't have made sense to build that around the lookup rbtree as its going away. It makes sense to use the range tree that we're going to keep using to make sure we don't accidentally introduce locks whose ranges overlap (which would lead to item cache inconsistency). Signed-off-by: Zach Brown <zab@versity.com> Signed-off-by: Chris Kirby <ckirby@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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