0.51: Only allow one active comp thread pre-checkpoint under -XX:+DebugOnRestore #21468
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…store Under -XX:+DebugOnRestore, the compiler generates a bunch of FSD bodies pre-checkpoint, and then proacively recompiles them without FSD in the checkpoint hook. If the queue gets big, more than one compilation thread may be activated; compilations in parallel generally require a distinct code cache per thread. However, because the code caches are backed by Huge Pages (which means touching a small part of the page brings the entire page into RSS), multiple compilation threads can cause the code bodies to get fragmented across multiple code caches (rather than being compacted in a smaller set) ultimately increasing the total RSS memory footprint. This change fixes this by only allowing one compilation thread pre-checkpoint (under -XX:+DebugOnRestore). While this increases the checkpoint time, it reduces the footprint post-restore caused by the increased code cache usage of -XX:+DebugOnRestore. Signed-off-by: Irwin D'Souza <[email protected]>
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Cherry-pick of #21453