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Chris Lu
8d388acc0e
* mount: tolerance-window write pattern detection for concurrent writeback WriterPattern decides whether each dirty chunk is buffered in RAM (NewMemChunk) or spilled to an on-disk swap file (NewSwapFileChunk), so a sequential stream misclassified as random is pushed through disk-backed swap. The old detector compared each write's start to the previous write's exact stop offset (atomic.Swap of lastWriteStopOffset, then lastOffset == offset). That is brittle under concurrent FUSE writeback: MonitorWriteAt runs before the per-handle write lock, so parallel Write upcalls interleave the swap, and writeback flushes dirty pages slightly out of offset order. A genuinely sequential stream then repeatedly reads as random and spills to swap. Replace the exact match with the same frontier + tolerance approach used on the read side: track a never-regressing max frontier (offset+size) via a CAS loop and treat a write whose start is within SeqTolerance (8 MiB) of that frontier as sequential. The existing +/-ModeChangeLimit hysteresis is kept, so a single outlier write can't flip the mode. Adds page_writer_pattern_test.go covering sequentiality, hysteresis, reorder tolerance, the inclusive tolerance boundary, frontier non-regression (the CAS invariant), and recovery back to sequential mode. * mount: read write frontier inside the CAS loop Capture the frontier from the CAS loop's own load rather than a separate up-front snapshot, so the sequentiality diff is judged against the freshest pre-image even if a concurrent writeback upcall advances the frontier while we loop. Also drops the now-redundant load. Behavior is unchanged for the single-threaded tests; addresses review feedback on #9984.