Add experimental.arenas.i.pactivep.

The new experimental mallctl exposes the arena pactive counter to applications,
which allows fast read w/o going through the mallctl / epoch steps.  This is
particularly useful when frequent balancing is required, e.g. when having
multiple manual arenas, and threads are multiplexed to them based on usage.

1 files changed, 82 insertions, 7 deletions

diff --git a/src/ctl.c b/src/ctl.c
index 271881e..1d83087 100644
--- a/src/ctl.c
+++ b/src/ctl.c
@@ -225,6 +225,8 @@ CTL_PROTO(experimental_hooks_install)
 CTL_PROTO(experimental_hooks_remove)
 CTL_PROTO(experimental_utilization_query)
 CTL_PROTO(experimental_utilization_batch_query)
+CTL_PROTO(experimental_arenas_i_pactivep)
+INDEX_PROTO(experimental_arenas_i)
 
 #define MUTEX_STATS_CTL_PROTO_GEN(n)					\
 CTL_PROTO(stats_##n##_num_ops)						\
@@ -588,19 +590,31 @@ static const ctl_named_node_t stats_node[] = {
 	{NAME("arenas"),	CHILD(indexed, stats_arenas)}
 };
 
-static const ctl_named_node_t hooks_node[] = {
+static const ctl_named_node_t experimental_hooks_node[] = {
 	{NAME("install"),	CTL(experimental_hooks_install)},
 	{NAME("remove"),	CTL(experimental_hooks_remove)}
 };
 
-static const ctl_named_node_t utilization_node[] = {
+static const ctl_named_node_t experimental_utilization_node[] = {
 	{NAME("query"),		CTL(experimental_utilization_query)},
 	{NAME("batch_query"),	CTL(experimental_utilization_batch_query)}
 };
 
+static const ctl_named_node_t experimental_arenas_i_node[] = {
+	{NAME("pactivep"),	CTL(experimental_arenas_i_pactivep)}
+};
+static const ctl_named_node_t super_experimental_arenas_i_node[] = {
+	{NAME(""),		CHILD(named, experimental_arenas_i)}
+};
+
+static const ctl_indexed_node_t experimental_arenas_node[] = {
+	{INDEX(experimental_arenas_i)}
+};
+
 static const ctl_named_node_t experimental_node[] = {
-	{NAME("hooks"),		CHILD(named, hooks)},
-	{NAME("utilization"),	CHILD(named, utilization)}
+	{NAME("hooks"),		CHILD(named, experimental_hooks)},
+	{NAME("utilization"),	CHILD(named, experimental_utilization)},
+	{NAME("arenas"),	CHILD(indexed, experimental_arenas)}
 };
 
 static const ctl_named_node_t	root_node[] = {
@@ -3068,15 +3082,23 @@ stats_arenas_i_extents_j_index(tsdn_t *tsdn, const size_t *mib,
 	return super_stats_arenas_i_extents_j_node;
 }
 
+static bool
+ctl_arenas_i_verify(size_t i) {
+	size_t a = arenas_i2a_impl(i, true, true);
+	if (a == UINT_MAX || !ctl_arenas->arenas[a]->initialized) {
+		return true;
+	}
+
+	return false;
+}
+
 static const ctl_named_node_t *
 stats_arenas_i_index(tsdn_t *tsdn, const size_t *mib,
     size_t miblen, size_t i) {
 	const ctl_named_node_t *ret;
-	size_t a;
 
 	malloc_mutex_lock(tsdn, &ctl_mtx);
-	a = arenas_i2a_impl(i, true, true);
-	if (a == UINT_MAX || !ctl_arenas->arenas[a]->initialized) {
+	if (ctl_arenas_i_verify(i)) {
 		ret = NULL;
 		goto label_return;
 	}
@@ -3351,3 +3373,56 @@ experimental_utilization_batch_query_ctl(tsd_t *tsd, const size_t *mib,
 label_return:
 	return ret;
 }
+
+static const ctl_named_node_t *
+experimental_arenas_i_index(tsdn_t *tsdn, const size_t *mib,
+    size_t miblen, size_t i) {
+	const ctl_named_node_t *ret;
+
+	malloc_mutex_lock(tsdn, &ctl_mtx);
+	if (ctl_arenas_i_verify(i)) {
+		ret = NULL;
+		goto label_return;
+	}
+	ret = super_experimental_arenas_i_node;
+label_return:
+	malloc_mutex_unlock(tsdn, &ctl_mtx);
+	return ret;
+}
+
+static int
+experimental_arenas_i_pactivep_ctl(tsd_t *tsd, const size_t *mib,
+    size_t miblen, void *oldp, size_t *oldlenp, void *newp, size_t newlen) {
+	if (!config_stats) {
+		return ENOENT;
+	}
+	if (oldp == NULL || oldlenp == NULL || *oldlenp != sizeof(size_t *)) {
+		return EINVAL;
+	}
+
+	unsigned arena_ind;
+	arena_t *arena;
+	int ret;
+	size_t *pactivep;
+
+	malloc_mutex_lock(tsd_tsdn(tsd), &ctl_mtx);
+	READONLY();
+	MIB_UNSIGNED(arena_ind, 2);
+	if (arena_ind < narenas_total_get() && (arena =
+	    arena_get(tsd_tsdn(tsd), arena_ind, false)) != NULL) {
+#if defined(JEMALLOC_GCC_ATOMIC_ATOMICS) ||				\
+    defined(JEMALLOC_GCC_SYNC_ATOMICS) || defined(_MSC_VER)
+		/* Expose the underlying counter for fast read. */
+		pactivep = (size_t *)&(arena->nactive.repr);
+		READ(pactivep, size_t *);
+		ret = 0;
+#else
+		ret = EFAULT;
+#endif
+	} else {
+		ret = EFAULT;
+	}
+label_return:
+	malloc_mutex_unlock(tsd_tsdn(tsd), &ctl_mtx);
+	return ret;
+}