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Skip redundant host function registration on reload - #422
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ludfjig merged 2 commits intoNov 12, 2026
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get_loaded_sandbox and unload each called RegisterHostModules, although the base snapshot already holds that registration. A load/unload cycle made four guest calls. Only register_handler and RunHandler are needed. Register host functions only when a restored snapshot records different ones than the builder supplies. On add_load_handle_unload this cuts 415 to 315 us on MSHV and 248 to 203 us on KVM. Bump the snapshot metadata schema to 2, since 0.5.0 snapshots can record host functions their base never registered. Signed-off-by: Ludvig Liljenberg <4257730+ludfjig@users.noreply.github.com>
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simongdavies
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A couple of questions but otherwise LGTM, I think we need to do release notes the same as for hyperlight as this has breaking changes and the move to hyperlight v0.19 will also cause breaking changes, I will look at this later.
Signed-off-by: Ludvig Liljenberg <4257730+ludfjig@users.noreply.github.com>
simongdavies
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get_loaded_sandboxandunloadeach calledRegisterHostModules, although the base snapshot already holds that registration. A load/unload cycle made four guest calls, but onlyregister_handlerandRunHandlerare needed. In hyperlight-dev/hyperlight-bench#46,kvm-hyperlight-js-reloadlost 15% throughput against 0.4.0.This change registers host functions only when a restored snapshot records different ones than the builder supplies. It then takes a new base snapshot, so later cycles skip registration.
full_lifecycle/add_load_handle_unload:KVM stays about 10% slower than 0.4.0 because each guest call costs more in Hyperlight 0.18.
Breaking: the snapshot metadata schema is now 2. Snapshots from 0.5.0 can record host functions their base never registered, so they are rejected and must be recreated.