Add arena-level name.

An arena-level name can help identify manual arenas.

src/arena.c

@@ -1547,6 +1547,22 @@ arena_dss_prec_set(arena_t *arena, dss_prec_t dss_prec) {
 	return false;
 }
 
+void
+arena_name_get(arena_t *arena, char *name) {
+	char *end = (char *)memchr((void *)arena->name, '\0', ARENA_NAME_LEN);
+	assert(end != NULL);
+	size_t len = (uintptr_t)end - (uintptr_t)arena->name + 1;
+	assert(len > 0 && len <= ARENA_NAME_LEN);
+
+	strncpy(name, arena->name, len);
+}
+
+void
+arena_name_set(arena_t *arena, const char *name) {
+	strncpy(arena->name, name, ARENA_NAME_LEN);
+	arena->name[ARENA_NAME_LEN - 1] = '\0';
+}
+
 ssize_t
 arena_dirty_decay_ms_default_get(void) {
 	return atomic_load_zd(&dirty_decay_ms_default, ATOMIC_RELAXED);
@@ -1670,6 +1686,11 @@ arena_new(tsdn_t *tsdn, unsigned ind, const arena_config_t *config) {
 	arena_set(ind, arena);
 	arena->ind = ind;
 
+	/* Init the name. */
+	malloc_snprintf(arena->name, sizeof(arena->name), "%s_%u",
+	    arena_is_auto(arena) ? "auto" : "manual", arena->ind);
+	arena->name[ARENA_NAME_LEN - 1] = '\0';
+
 	nstime_init_update(&arena->create_time);
 
 	/*

src/ctl.c

@@ -170,6 +170,7 @@ CTL_PROTO(arena_i_dirty_decay_ms)
 CTL_PROTO(arena_i_muzzy_decay_ms)
 CTL_PROTO(arena_i_extent_hooks)
 CTL_PROTO(arena_i_retain_grow_limit)
+CTL_PROTO(arena_i_name)
 INDEX_PROTO(arena_i)
 CTL_PROTO(arenas_bin_i_size)
 CTL_PROTO(arenas_bin_i_nregs)
@@ -504,11 +505,12 @@ static const ctl_named_node_t arena_i_node[] = {
 	 * Undocumented for now, since we anticipate an arena API in flux after
 	 * we cut the last 5-series release.
 	 */
-	{NAME("oversize_threshold"), CTL(arena_i_oversize_threshold)},
-	{NAME("dirty_decay_ms"), CTL(arena_i_dirty_decay_ms)},
-	{NAME("muzzy_decay_ms"), CTL(arena_i_muzzy_decay_ms)},
-	{NAME("extent_hooks"),	CTL(arena_i_extent_hooks)},
-	{NAME("retain_grow_limit"),	CTL(arena_i_retain_grow_limit)}
+	{NAME("oversize_threshold"),	CTL(arena_i_oversize_threshold)},
+	{NAME("dirty_decay_ms"),	CTL(arena_i_dirty_decay_ms)},
+	{NAME("muzzy_decay_ms"),	CTL(arena_i_muzzy_decay_ms)},
+	{NAME("extent_hooks"),		CTL(arena_i_extent_hooks)},
+	{NAME("retain_grow_limit"),	CTL(arena_i_retain_grow_limit)},
+	{NAME("name"),			CTL(arena_i_name)}
 };
 static const ctl_named_node_t super_arena_i_node[] = {
 	{NAME(""),		CHILD(named, arena_i)}
@@ -2983,6 +2985,61 @@ label_return:
 	return ret;
 }
 
+/*
+ * When writing, newp should point to a char array storing the name to be set.
+ * A name longer than ARENA_NAME_LEN will be arbitrarily cut. When reading,
+ * oldp should point to a char array whose length is no shorter than
+ * ARENA_NAME_LEN or the length of the name when it was set.
+ */
+static int
+arena_i_name_ctl(tsd_t *tsd, const size_t *mib, size_t miblen,
+    void *oldp, size_t *oldlenp, void *newp, size_t newlen) {
+	int ret;
+	unsigned arena_ind;
+	char *name;
+
+	malloc_mutex_lock(tsd_tsdn(tsd), &ctl_mtx);
+	MIB_UNSIGNED(arena_ind, 1);
+	if (arena_ind == MALLCTL_ARENAS_ALL || arena_ind >=
+	    ctl_arenas->narenas) {
+		ret = EINVAL;
+		goto label_return;
+	}
+	arena_t *arena = arena_get(tsd_tsdn(tsd), arena_ind, false);
+	if (arena == NULL) {
+		ret = EFAULT;
+		goto label_return;
+	}
+
+	if (oldp != NULL && oldlenp != NULL) {
+		/*
+		 * Read the arena name.  When reading, the input oldp should
+		 * point to an array with a length no shorter than
+		 * ARENA_NAME_LEN or the length when it was set.
+		 */
+		if (*oldlenp != sizeof(char *)) {
+			ret = EINVAL;
+			goto label_return;
+		}
+		name = *(char **)oldp;
+		arena_name_get(arena, name);
+	}
+
+	if (newp != NULL) {
+		/* Write the arena name. */
+		WRITE(name, char *);
+		if (name == NULL) {
+			ret = EINVAL;
+			goto label_return;
+		}
+		arena_name_set(arena, name);
+	}
+	ret = 0;
+label_return:
+	malloc_mutex_unlock(tsd_tsdn(tsd), &ctl_mtx);
+	return ret;
+}
+
 static const ctl_named_node_t *
 arena_i_index(tsdn_t *tsdn, const size_t *mib, size_t miblen,
     size_t i) {

src/stats.c

@@ -42,15 +42,18 @@ const char *arena_mutex_names[mutex_prof_num_arena_mutexes] = {
 	assert(miblen_new == miblen + 1);				\
 } while (0)
 
-#define CTL_M2_GET(n, i, v, t) do {					\
+#define CTL_MIB_GET(n, i, v, t, ind) do {				\
 	size_t mib[CTL_MAX_DEPTH];					\
 	size_t miblen = sizeof(mib) / sizeof(size_t);			\
 	size_t sz = sizeof(t);						\
 	xmallctlnametomib(n, mib, &miblen);				\
-	mib[2] = (i);							\
+	mib[(ind)] = (i);							\
 	xmallctlbymib(mib, miblen, (void *)v, &sz, NULL, 0);		\
 } while (0)
 
+#define CTL_M1_GET(n, i, v, t) CTL_MIB_GET(n, i, v, t, 1)
+#define CTL_M2_GET(n, i, v, t) CTL_MIB_GET(n, i, v, t, 2)
+
 /******************************************************************************/
 /* Data. */
 
@@ -1042,6 +1045,8 @@ JEMALLOC_COLD
 static void
 stats_arena_print(emitter_t *emitter, unsigned i, bool bins, bool large,
     bool mutex, bool extents, bool hpa) {
+	char name[ARENA_NAME_LEN];
+	char *namep = name;
 	unsigned nthreads;
 	const char *dss;
 	ssize_t dirty_decay_ms, muzzy_decay_ms;
@@ -1059,6 +1064,10 @@ stats_arena_print(emitter_t *emitter, unsigned i, bool bins, bool large,
 	uint64_t uptime;
 
 	CTL_GET("arenas.page", &page, size_t);
+	if (i != MALLCTL_ARENAS_ALL && i != MALLCTL_ARENAS_DESTROYED) {
+		CTL_M1_GET("arena.0.name", i, (void *)&namep, const char *);
+		emitter_kv(emitter, "name", "name", emitter_type_string, &namep);
+	}
 
 	CTL_M2_GET("stats.arenas.0.nthreads", i, &nthreads, unsigned);
 	emitter_kv(emitter, "nthreads", "assigned threads",