Hi. It turns out there is a hard cap which might be worth documenting.
Index: lib/libc/sys/sysctl.2
===================================================================
RCS file: /cvs/src/lib/libc/sys/sysctl.2,v
retrieving revision 1.11
diff -u -p -r1.11 sysctl.2
--- lib/libc/sys/sysctl.2 30 Sep 2018 18:58:17 -0000 1.11
+++ lib/libc/sys/sysctl.2 29 Jan 2019 10:08:18 -0000
@@ -535,6 +535,7 @@ This structure contains the time that th
.It Dv KERN_CACHEPCT Pq Va kern.bufcachepercent
The maximum percentage of physical memory the buffer cache may use;
the default is 20%.
+The buffer cache is capped at 3.2GB.
.It Dv KERN_CCPU Pq Va kern.ccpu
The scheduler exponential decay value.
.It Dv KERN_CLOCKRATE Pq Va kern.clockrate
