Make jemalloc(3) default to retain:true, like it does on Linux
and OSX. This results in significantly fewer calls to mmap(2).
For example, here's the diff of truss output for id(1):
```
--- bez 2020-02-27 18:41:46.374698000 +0000
+++ z 2020-02-27 18:41:57.547764000 +0000
@@ -26,55 +26,24 @@ mprotect(0x800424000,36864,PROT_READ) = 0 (0x0)
sysarch(AMD64_SET_FSBASE,0x7fffffffda20) = 0 (0x0)
mprotect(0x800424000,36864,PROT_READ|PROT_WRITE) = 0 (0x0)
mprotect(0x800424000,36864,PROT_READ) = 0 (0x0)
-readlink("/etc/malloc.conf",0x7fffffffd130,1024) ERR#2 'No such file or directory'
+readlink("/etc/malloc.conf","retain:true,junk:false",1024) = 22 (0x16)
issetugid() = 0 (0x0)
__sysctl("vm.overcommit",2,0x7fffffffd0dc,0x7fffffffd0d0,0x0,0) = 0 (0x0)
mmap(0x0,2097152,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(21),-1,0x0) = 34368126976 (0x800800000)
-mmap(0x0,32768,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366410752 (0x80065d000)
-mmap(0x0,4194304,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(21),-1,0x0) = 34370224128 (0x800a00000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34362114048 (0x800244000)
+mmap(0x0,2097152,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34370224128 (0x800a00000)
+mmap(0x0,4194304,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(21),-1,0x0) = 34372321280 (0x800c00000)
mprotect(0x204000,4096,PROT_READ) = 0 (0x0)
getuid() = 1000 (0x3e8)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366443520 (0x800665000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366447616 (0x800666000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366451712 (0x800667000)
fstatat(AT_FDCWD,"/etc/nsswitch.conf",{ mode=-rw-r--r-- ,inode=2167112,size=338,blksize=32768 },0x0) = 0 (0x0)
open("/etc/nsswitch.conf",O_RDONLY|O_CLOEXEC,0666) = 3 (0x3)
-mmap(0x0,28672,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366455808 (0x800668000)
-mmap(0x0,28672,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366484480 (0x80066f000)
-mmap(0x0,20480,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366513152 (0x800676000)
-mmap(0x0,20480,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366533632 (0x80067b000)
fstat(3,{ mode=-rw-r--r-- ,inode=2167112,size=338,blksize=32768 }) = 0 (0x0)
-mmap(0x0,36864,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366554112 (0x800680000)
read(3,"#\n# nsswitch.conf(5) - name ser"...,32768) = 338 (0x152)
-read(3,0x800680180,32768) = 0 (0x0)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366590976 (0x800689000)
-mmap(0x0,20480,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366595072 (0x80068a000)
-mmap(0x0,12288,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366615552 (0x80068f000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366627840 (0x800692000)
-mmap(0x0,12288,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366631936 (0x800693000)
+read(3,0x800a24180,32768) = 0 (0x0)
close(3) = 0 (0x0)
geteuid() = 1000 (0x3e8)
-mmap(0x0,12288,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366644224 (0x800696000)
open("/etc/pwd.db",O_RDONLY|O_CLOEXEC,00) = 3 (0x3)
fstat(3,{ mode=-rw-r--r-- ,inode=2167182,size=40960,blksize=32768 }) = 0 (0x0)
read(3,"\0\^F\^Ua\0\0\0\^B\0\0\^P\M-a\0"...,260) = 260 (0x104)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366656512 (0x800699000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366660608 (0x80069a000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366664704 (0x80069b000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366668800 (0x80069c000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366672896 (0x80069d000)
-mmap(0x0,12288,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366676992 (0x80069e000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366689280 (0x8006a1000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366693376 (0x8006a2000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366697472 (0x8006a3000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366701568 (0x8006a4000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366705664 (0x8006a5000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366709760 (0x8006a6000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366713856 (0x8006a7000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366717952 (0x8006a8000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366722048 (0x8006a9000)
-mmap(0x0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON|MAP_ALIGNED(12),-1,0x0) = 34366726144 (0x8006aa000)
pread(3,"\0*\^O\M-x\^O\M-w\^O\M-r\^O\M-&"...,4096,0x6000) = 4096 (0x1000)
pread(3,"\0&\^O\M-{\^O\M->\^O\M-9\^Oz\^Ou"...,4096,0x4000) = 4096 (0x1000)
pread(3,"\0.\^O\M-{\^O\M-/\^O\M-*\^OU\^OP"...,4096,0x5000) = 4096 (0x1000)
@@ -85,7 +54,7 @@ pread(3,"\0 \^O\M-{\^O\M->\^O\M-9\^Ol\^Of"...,4096,0x2
pread(3,"\0"\^O\M-|\^O\M-0\^O\M-,\^Oq\^Ol"...,4096,0x3000) = 4096 (0x1000)
close(3) = 0 (0x0)
__sysctl("kern.ngroups",2,0x7fffffffe3cc,0x7fffffffe3d0,0x0,0) = 0 (0x0)
-getgroups(0x400,0x8006a3000) = 4 (0x4)
+getgroups(0x400,0x800a47000) = 4 (0x4)
fstat(1,{ mode=crw--w---- ,inode=715,size=0,blksize=4096 }) = 0 (0x0)
ioctl(1,TIOCGETA,0x7fffffffdda0) = 0 (0x0)
open("/etc/group",O_RDONLY|O_CLOEXEC,0666) = 3 (0x3)
```