Decay: Move in arena decay functions.

src/decay.c

@@ -1,3 +1,177 @@
 #include "jemalloc/internal/jemalloc_preamble.h"
 #include "jemalloc/internal/jemalloc_internal_includes.h"
 
+#include "jemalloc/internal/decay.h"
+
+/*
+ * Generate a new deadline that is uniformly random within the next epoch after
+ * the current one.
+ */
+void
+decay_deadline_init(decay_t *decay) {
+	nstime_copy(&decay->deadline, &decay->epoch);
+	nstime_add(&decay->deadline, &decay->interval);
+	if (decay_ms_read(decay) > 0) {
+		nstime_t jitter;
+
+		nstime_init(&jitter, prng_range_u64(&decay->jitter_state,
+		    nstime_ns(&decay->interval)));
+		nstime_add(&decay->deadline, &jitter);
+	}
+}
+
+void
+decay_reinit(decay_t *decay, ssize_t decay_ms) {
+	atomic_store_zd(&decay->time_ms, decay_ms, ATOMIC_RELAXED);
+	if (decay_ms > 0) {
+		nstime_init(&decay->interval, (uint64_t)decay_ms *
+		    KQU(1000000));
+		nstime_idivide(&decay->interval, SMOOTHSTEP_NSTEPS);
+	}
+
+	nstime_init_update(&decay->epoch);
+	decay->jitter_state = (uint64_t)(uintptr_t)decay;
+	decay_deadline_init(decay);
+	decay->nunpurged = 0;
+	memset(decay->backlog, 0, SMOOTHSTEP_NSTEPS * sizeof(size_t));
+}
+
+bool
+decay_init(decay_t *decay, ssize_t decay_ms) {
+	if (config_debug) {
+		for (size_t i = 0; i < sizeof(decay_t); i++) {
+			assert(((char *)decay)[i] == 0);
+		}
+		decay->ceil_npages = 0;
+	}
+	if (malloc_mutex_init(&decay->mtx, "decay", WITNESS_RANK_DECAY,
+	    malloc_mutex_rank_exclusive)) {
+		return true;
+	}
+	decay->purging = false;
+	decay_reinit(decay, decay_ms);
+	return false;
+}
+
+bool
+decay_ms_valid(ssize_t decay_ms) {
+	if (decay_ms < -1) {
+		return false;
+	}
+	if (decay_ms == -1 || (uint64_t)decay_ms <= NSTIME_SEC_MAX *
+	    KQU(1000)) {
+		return true;
+	}
+	return false;
+}
+
+static void
+decay_maybe_update_time(decay_t *decay, nstime_t *new_time) {
+	if (unlikely(!nstime_monotonic() && nstime_compare(&decay->epoch,
+	    new_time) > 0)) {
+		/*
+		 * Time went backwards.  Move the epoch back in time and
+		 * generate a new deadline, with the expectation that time
+		 * typically flows forward for long enough periods of time that
+		 * epochs complete.  Unfortunately, this strategy is susceptible
+		 * to clock jitter triggering premature epoch advances, but
+		 * clock jitter estimation and compensation isn't feasible here
+		 * because calls into this code are event-driven.
+		 */
+		nstime_copy(&decay->epoch, new_time);
+		decay_deadline_init(decay);
+	} else {
+		/* Verify that time does not go backwards. */
+		assert(nstime_compare(&decay->epoch, new_time) <= 0);
+	}
+}
+
+static size_t
+decay_backlog_npages_limit(const decay_t *decay) {
+	/*
+	 * For each element of decay_backlog, multiply by the corresponding
+	 * fixed-point smoothstep decay factor.  Sum the products, then divide
+	 * to round down to the nearest whole number of pages.
+	 */
+	uint64_t sum = 0;
+	for (unsigned i = 0; i < SMOOTHSTEP_NSTEPS; i++) {
+		sum += decay->backlog[i] * h_steps[i];
+	}
+	size_t npages_limit_backlog = (size_t)(sum >> SMOOTHSTEP_BFP);
+
+	return npages_limit_backlog;
+}
+
+static void
+decay_backlog_update(decay_t *decay, uint64_t nadvance_u64,
+    size_t current_npages) {
+	if (nadvance_u64 >= SMOOTHSTEP_NSTEPS) {
+		memset(decay->backlog, 0, (SMOOTHSTEP_NSTEPS-1) *
+		    sizeof(size_t));
+	} else {
+		size_t nadvance_z = (size_t)nadvance_u64;
+
+		assert((uint64_t)nadvance_z == nadvance_u64);
+
+		memmove(decay->backlog, &decay->backlog[nadvance_z],
+		    (SMOOTHSTEP_NSTEPS - nadvance_z) * sizeof(size_t));
+		if (nadvance_z > 1) {
+			memset(&decay->backlog[SMOOTHSTEP_NSTEPS -
+			    nadvance_z], 0, (nadvance_z-1) * sizeof(size_t));
+		}
+	}
+
+	size_t npages_delta = (current_npages > decay->nunpurged) ?
+	    current_npages - decay->nunpurged : 0;
+	decay->backlog[SMOOTHSTEP_NSTEPS-1] = npages_delta;
+
+	if (config_debug) {
+		if (current_npages > decay->ceil_npages) {
+			decay->ceil_npages = current_npages;
+		}
+		size_t npages_limit = decay_backlog_npages_limit(decay);
+		assert(decay->ceil_npages >= npages_limit);
+		if (decay->ceil_npages > npages_limit) {
+			decay->ceil_npages = npages_limit;
+		}
+	}
+}
+
+static inline bool
+decay_deadline_reached(const decay_t *decay, const nstime_t *time) {
+	return (nstime_compare(&decay->deadline, time) <= 0);
+}
+
+bool
+decay_maybe_advance_epoch(decay_t *decay, nstime_t *new_time,
+    size_t npages_current) {
+	/* Handle possible non-monotonicity of time. */
+	decay_maybe_update_time(decay, new_time);
+
+	if (!decay_deadline_reached(decay, new_time)) {
+		return false;
+	}
+	nstime_t delta;
+	nstime_copy(&delta, new_time);
+	nstime_subtract(&delta, &decay->epoch);
+
+	uint64_t nadvance_u64 = nstime_divide(&delta, &decay->interval);
+	assert(nadvance_u64 > 0);
+
+	/* Add nadvance_u64 decay intervals to epoch. */
+	nstime_copy(&delta, &decay->interval);
+	nstime_imultiply(&delta, nadvance_u64);
+	nstime_add(&decay->epoch, &delta);
+
+	/* Set a new deadline. */
+	decay_deadline_init(decay);
+
+	/* Update the backlog. */
+	decay_backlog_update(decay, nadvance_u64, npages_current);
+
+	decay->npages_limit = decay_backlog_npages_limit(decay);
+	decay->nunpurged = (decay->npages_limit > npages_current) ?
+	    decay->npages_limit : npages_current;
+
+	return true;
+}