Function background_thread_interval_check

deps/jemalloc/src/background_thread.c:656–737

Check if we need to signal the background thread early. */

/* Check if we need to signal the background thread early. */
void
background_thread_interval_check(tsdn_t *tsdn, arena_t *arena,
    arena_decay_t *decay, size_t npages_new) {
	background_thread_info_t *info = arena_background_thread_info_get(
	    arena);
	if (malloc_mutex_trylock(tsdn, &info->mtx)) {
		/*
		 * Background thread may hold the mutex for a long period of
		 * time.  We'd like to avoid the variance on application
		 * threads.  So keep this non-blocking, and leave the work to a
		 * future epoch.
		 */
		return;
	}

	if (info->state != background_thread_started) {
		goto label_done;
	}
	if (malloc_mutex_trylock(tsdn, &decay->mtx)) {
		goto label_done;
	}

	ssize_t decay_time = atomic_load_zd(&decay->time_ms, ATOMIC_RELAXED);
	if (decay_time <= 0) {
		/* Purging is eagerly done or disabled currently. */
		goto label_done_unlock2;
	}
	uint64_t decay_interval_ns = nstime_ns(&decay->interval);
	assert(decay_interval_ns > 0);

	nstime_t diff;
	nstime_init(&diff, background_thread_wakeup_time_get(info));
	if (nstime_compare(&diff, &decay->epoch) <= 0) {
		goto label_done_unlock2;
	}
	nstime_subtract(&diff, &decay->epoch);
	if (nstime_ns(&diff) < BACKGROUND_THREAD_MIN_INTERVAL_NS) {
		goto label_done_unlock2;
	}

	if (npages_new > 0) {
		size_t n_epoch = (size_t)(nstime_ns(&diff) / decay_interval_ns);
		/*
		 * Compute how many new pages we would need to purge by the next
		 * wakeup, which is used to determine if we should signal the
		 * background thread.
		 */
		uint64_t npurge_new;
		if (n_epoch >= SMOOTHSTEP_NSTEPS) {
			npurge_new = npages_new;
		} else {
			uint64_t h_steps_max = h_steps[SMOOTHSTEP_NSTEPS - 1];
			assert(h_steps_max >=
			    h_steps[SMOOTHSTEP_NSTEPS - 1 - n_epoch]);
			npurge_new = npages_new * (h_steps_max -
			    h_steps[SMOOTHSTEP_NSTEPS - 1 - n_epoch]);
			npurge_new >>= SMOOTHSTEP_BFP;
		}