FreeBSD Port: dns/bind920 steadily increasing memory usage

[Felix J. Ogris]

Hi,

I have noticed that Bind 9.20.x on FreeBSD 14.2 and 14.3 consumes more and more memory when being used as a resolver.
While top reports a SIZE of 4800 MB and RES of 4600 MB, the XML statistics channel just reports 209053061 bytes for both malloced and in use. This instance has been running for about 11 days.
Relevant named.conf snippets:

zone-statistics no;
dnssec-validation no;
max-cache-size 1024M;

memstatistics has not been set.

There are 169 (3 automatic) zones configured statically to ground zone "127.in-addr.arpa", zone "example.com", and such. No RPZs, no dynamic zone updates. It runs as unprivileged user in a chroot on a VM with 2 CPU cores.
rndc flush did never release any memory. Instead, I sporadically observed SIZE increasing as soon as rndc flush returned.
On the very same system, Bind 9.18.x levels off around 300-400 megs, even when it had been running for several weeks.
Both 9.20.x and 9.18.x were compiled locally from the FreeBSD ports system using just these four options:

IDN (International Domain Names support)
TCP_FASTOPEN (RFC 7413 support)
STATS_XML (Enable XML statistics channel)
GSSAPI_NONE

FreeBSD 14.3 provides clang version 19.1.7 as C compiler, and jemalloc 5.2.1-0 as system memory allocator. Machine type is amd64.
As the memory usage of my resolver at home grows more slowly, I assume the growth rate depends on the number of queries and/or answers.
When being used as an authorative server, Bind 9.20 uses very little memory and does not increase, comparable to 9.18.
I am willed to debug this behaviour, but will need support to do so. Any suggestions are welcome.

-Felix