From 5dead37a9d38494341a6808bd09b8896282becc1 Mon Sep 17 00:00:00 2001
From: David Goldblatt <davidgoldblatt@fb.com>
Date: Wed, 13 May 2020 12:20:30 -0700
Subject: [PATCH] Allow narenas:default.

This can be useful when you know you want to override some lower-priority
configuration setting with its default value, but don't know what that value
would be.
---
 src/jemalloc.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/jemalloc.c b/src/jemalloc.c
index 78da45bc..d5d54e2d 100644
--- a/src/jemalloc.c
+++ b/src/jemalloc.c
@@ -1282,9 +1282,17 @@ malloc_conf_init_helper(sc_data_t *sc_data, unsigned bin_shard_sizes[SC_NBINS],
 				}
 				CONF_CONTINUE;
 			}
-			CONF_HANDLE_UNSIGNED(opt_narenas, "narenas", 1,
-			    UINT_MAX, CONF_CHECK_MIN, CONF_DONT_CHECK_MAX,
-			    false)
+			if (CONF_MATCH("narenas")) {
+				if (CONF_MATCH_VALUE("default")) {
+					opt_narenas = 0;
+					CONF_CONTINUE;
+				} else {
+					CONF_HANDLE_UNSIGNED(opt_narenas,
+					    "narenas", 1, UINT_MAX,
+					    CONF_CHECK_MIN, CONF_DONT_CHECK_MAX,
+					    /* clip */ false)
+				}
+			}
 			if (CONF_MATCH("bin_shards")) {
 				const char *bin_shards_segment_cur = v;
 				size_t vlen_left = vlen;