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Server code that wants to dirty blocks by holding a commit won't be allowed to until the current allocators for the server transaction have enough space for the holder. As an active holder applies the commit the allocators are refilled and the waiting holders will proceed. But the current allocators can have no resources as the server starts up. There will never be active holders to apply the commit and refill the allocators. In this case all the holders will block indefinitely. The fix is to trigger a server commit when a holder doesn't have room. It used to be that commits were only triggered when apply callers were waiting. We transfer some of that logic into a new 'committing' field so that we can have commits in flight without apply callers waiting. We add it to the server commit tracing. While we're at it we clean up the logic that tests if a hold can proceed. It used to be confusingly split across two functions that both could sample the current allocator space remaining. This could lead to weird cases where the first holder could use the second alloc remaining call, not the one whose values were tested to see if the holder could fit. Now each hold check only samples the allocators once. And finally we fix a subtle case where the budget exceeded message can spuriously trigger in the case where dirtying the freed list created a new empty block after the holder recorded the amount of space in the freed block. 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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