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in a debugging feature causing M_NOWAIT allocations to fail at a specified rate. This can be useful for detecting poor handling of M_NOWAIT: the most frequent problems I've bumped into are unconditional deference of the pointer even though it's NULL, and hangs as a result of a lost event where memory for the event couldn't be allocated. Two sysctls are added: debug.malloc.failure_rate How often to generate a failure: if set to 0 (default), this feature is disabled. Otherwise, the frequency of failures -- I've been using 10 (one in ten mallocs fails), but other popular settings might be much lower or much higher. debug.malloc.failure_count Number of times a coerced malloc failure has occurred as a result of this feature. Useful for tracking what might have happened and whether failures are being generated. Useful possible additions: tying failure rate to malloc type, printfs indicating the thread that experienced the coerced failure. Reviewed by: jeffr, jhb
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