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The pager turns page numbers into pinned in-memory frames and owns the buffer pool. Frames are carved from a single arena so the pool is one GC object and each page slice is stable for the pool's lifetime. Get/Unpin is the pin contract the cores will use; Allocate/Free is the page lifecycle; Checkpoint flushes dirty frames, persists the freelist to trunk pages, and fsyncs to make the main file a torn-free image. Replacement is CLOCK with a bounded sweep that fails cleanly when every frame is pinned rather than blocking. Dirty victims can be written back mid-flight because a page is never dirtied before its WAL batch is durable, so an early flush only moves committed bytes home. Concurrency is single-mutex for now. The lock-free read path and sharded page table the spec describes are a later optimization that does not change these signatures.
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First vertical slice of M1: the pager that sits between the storage cores and the file.
What this adds
pager.Pagerover thevfsseam: page numbers in, pinned in-memory frames out.Get/Unpinpin contract,Allocate/Freepage lifecycle,Checkpoint(lsn)durability boundary.Open.Design notes
Intent(Read/Write) is advisory this milestone; dirtiness is declared atUnpin.Tests
go test -race ./...green. Pager tests cover create/reopen round-trip, eviction round-trip (64 pages through an 8-frame pool), checkpoint durability across a simulated memfs crash, allocate/free reuse with freelist persistence, and clean pool-exhaustion failure.Implementation doc:
notes/Spec/2059/implementation/04-pager.md.