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This pull request introduces a loadRolldown utility to dynamically load the rolldown module while temporarily setting MIMALLOC_PURGE_DELAY=0. This configures the embedded mimalloc allocator to immediately purge freed arena memory, reducing peak RSS in single-run CLI builds. The utility is integrated into the chunk optimizer and library bundler, accompanied by unit tests. Feedback recommends resetting the cached rolldownPromise to undefined upon import failure to allow recovery in long-running processes like watch mode.
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Rolldown's native binding statically links mimalloc v3, which defaults to a 4-second arena purge delay (MIMALLOC_PURGE_DELAY=1000 * MIMALLOC_ARENA_PURGE_MULT=4) and only executes scheduled purges cooperatively during subsequent allocations. In single-run CLI builds where Rolldown is not invoked again after bundling completes, non-zero purge delays prevent freed arena pages from being returned to the OS, increasing peak RSS when subsequent post-bundle stages run. Introduce a shared loadRolldown() helper used by both the application chunk optimizer and the library builder that temporarily sets MIMALLOC_PURGE_DELAY=0 (when not already configured in the environment) while loading Rolldown's native binding so mimalloc caches a 0ms purge delay without leaving the variable set in process.env.
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Rolldown's native binding statically links mimalloc v3, which defaults to a 4-second arena purge delay (MIMALLOC_PURGE_DELAY=1000 * MIMALLOC_ARENA_PURGE_MULT=4) and only executes scheduled purges cooperatively during subsequent allocations. In single-run CLI builds where Rolldown is not invoked again after bundling completes, non-zero purge delays prevent freed arena pages from being returned to the OS, increasing peak RSS when subsequent post-bundle stages run.
Introduce a shared loadRolldown() helper used by both the application chunk optimizer and the library builder that temporarily sets MIMALLOC_PURGE_DELAY=0 (when not already configured in the environment) while loading Rolldown's native binding so mimalloc caches a 0ms purge delay without leaving the variable set in process.env.