FreeBSD Port: dns/bind920 JSON statistics channel leads to increasing memory usage

[Felix J. Ogris]

Hi,

BIND 9.20.26 linked against json-c 0.19 on FreeBSD 15.1 consumes more and more memory if you query its JSON statistics channel, around 500k to 1 meg per query. With json-c 0.18 or if you query the XML statistics channel, memory usage remains almost constant. Linux is unaffected.

named -V:
BIND 9.20.26 (Stable Release) <id:>
running on FreeBSD amd64 15.1-RELEASE-p2 FreeBSD 15.1-RELEASE-p2 releng/15.1-n283596-aadd58dddcbc GENERIC (FreeBSD 15.1-RELEASE-p2)
built by make with  '--enable-dnsrps' '--localstatedir=/var' '--sysconfdir=/usr/local/etc/namedb' '--with-openssl=/usr' '--with-readline=libedit' '--disable-tracing' '--disable-dnstap' '--disable-fixed-rrset' '--disable-geoip' '--without-maxminddb' '--without-gssapi' '--with-libidn2=/usr/local' '--disable-largefile' '--without-lmdb' '--disable-querytrace' '--with-json-c' '--with-libxml2' '--enable-tcp-fastopen' '--prefix=/usr/local' '--mandir=/usr/local/share/man' '--disable-silent-rules' '--infodir=/usr/local/share/info/' '--build=amd64-portbld-freebsd15.1' 'build_alias=amd64-portbld-freebsd15.1' 'CC=cc' 'CFLAGS=-O2 -pipe  -DLIBICONV_PLUG -fstack-protector-strong -isystem /usr/local/include -fno-strict-aliasing ' 'LDFLAGS= -L/usr/local/lib -ljson-c  ' 'LIBS=-L/usr/local/lib' 'CPPFLAGS=-DLIBICONV_PLUG -isystem /usr/local/include' 'CPP=cpp' 'PKG_CONFIG=pkgconf' 'PKG_CONFIG_LIBDIR=/usr/ports/dns/bind920/work/.pkgconfig:/usr/local/libdata/pkgconfig:/usr/local/share/pkgconfig:/usr/libdata/pkgconfig'
compiled by CLANG FreeBSD Clang 19.1.7 (https://github.com/llvm/llvm-project.git llvmorg-19.1.7-0-gcd708029e0b2)
compiled with OpenSSL version: OpenSSL 3.5.6 7 Apr 2026
linked to OpenSSL version: OpenSSL 3.5.6 7 Apr 2026
compiled with libuv version: 1.52.1
linked to libuv version: 1.52.1
compiled with liburcu version: 0.15.6
compiled with system jemalloc version: 2024073001
compiled with libnghttp2 version: 1.69.0
linked to libnghttp2 version: 1.69.0
compiled with libxml2 version: 2.15.3
linked to libxml2 version: 21503
compiled with json-c version: 0.19
linked to json-c version: 0.19
compiled with zlib version: 1.3.2
linked to zlib version: 1.3.2
threads support is enabled

My /etc/malloc.conf is symlinked to "retain:false" to let jemalloc release unused memory immediately.

How to trigger this behaviour on an otherwise idle system:

$ date
Thu Jul 30 21:54:35 CEST 2026
$ ps axuww | grep -E "^USER|sbin/named" | grep -v grep
USER       PID  %CPU %MEM    VSZ   RSS TT  STAT STARTED     TIME COMMAND
bind     28389   0.0  0.5  61260 30556  -  Is   21:53    0:00.16 /usr/local/sbin/named -u bind -c /usr/local/etc/namedb/named.conf
$ for i in `jot 1000`; do fetch -q -o /dev/null http://127.0.0.1:8053/json; done
$ date
Thu Jul 30 21:55:41 CEST 2026
$ ps axuww | grep -E "^USER|sbin/named" | grep -v grep
USER       PID  %CPU %MEM    VSZ    RSS TT  STAT STARTED     TIME COMMAND
bind     28389  23.2  9.5 631780 592084  -  Ss   21:53    0:08.30 /usr/local/sbin/named -u bind -c /usr/local/etc/namedb/named.conf
$

Even after a while memory isn't released:

$ date
Thu Jul 30 22:21:12 CEST 2026
$ ps axuww | grep -E "^USER|sbin/named" | grep -v grep
USER       PID  %CPU %MEM    VSZ    RSS TT  STAT STARTED     TIME COMMAND
bind     28389   0.0  9.7 646656 606956  -  Is   21:53    0:08.80 /usr/local/sbin/named -u bind -c /usr/local/etc/namedb/named.conf
$

When comparing json-c 0.18 to 0.19, I noticed a rewrite of json_object_put() which calls _json_object_put_maybe_free(). I assume this somehow leads to a memory leak just on FreeBSD like unpatched liburcu < 0.15.6.

BR,
Felix