brew install jemalloc

❯ find /usr -iname "*jemalloc*"

find: /usr/sbin/authserver: Permission denied
/usr/local/bin/jemalloc-config
/usr/local/bin/jemalloc.sh
/usr/local/include/jemalloc
/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/jemalloc.rb
/usr/local/var/homebrew/linked/jemalloc
/usr/local/lib/pkgconfig/jemalloc.pc
/usr/local/lib/libjemalloc.a
/usr/local/lib/libjemalloc.2.dylib
/usr/local/lib/libjemalloc_pic.a
/usr/local/lib/libjemalloc.dylib
/usr/local/opt/jemalloc
find: /usr/local/mysql-8.0.19-macos10.15-x86_64/keyring: Permission denied
find: /usr/local/mysql-8.0.19-macos10.15-x86_64/data: Permission denied
/usr/local/Cellar/jemalloc
/usr/local/Cellar/jemalloc/5.3.0/bin/jemalloc-config
/usr/local/Cellar/jemalloc/5.3.0/bin/jemalloc.sh
/usr/local/Cellar/jemalloc/5.3.0/.brew/jemalloc.rb
/usr/local/Cellar/jemalloc/5.3.0/include/jemalloc
/usr/local/Cellar/jemalloc/5.3.0/include/jemalloc/jemalloc.h
/usr/local/Cellar/jemalloc/5.3.0/lib/pkgconfig/jemalloc.pc
/usr/local/Cellar/jemalloc/5.3.0/lib/libjemalloc.a
/usr/local/Cellar/jemalloc/5.3.0/lib/libjemalloc.2.dylib
/usr/local/Cellar/jemalloc/5.3.0/lib/libjemalloc_pic.a
/usr/local/Cellar/jemalloc/5.3.0/lib/libjemalloc.dylib
/usr/local/Cellar/jemalloc/5.3.0/share/man/man3/jemalloc.3
/usr/local/Cellar/jemalloc/5.3.0/share/doc/jemalloc
/usr/local/Cellar/jemalloc/5.3.0/share/doc/jemalloc/jemalloc.html
/usr/local/share/man/man3/jemalloc.3
/usr/local/share/doc/jemalloc

cd /usr/local/opt/jemalloc/bin

./jemalloc.sh

export DYLD_INSERT_LIBRARIES=/usr/local/lib/libjemalloc.2.dylib

to check if it applied.

MALLOC_CONF=stats_print:true ruby -e "exit"

If you can see the result, it has been succefully applied.

___ Begin jemalloc statistics ___
Version: "5.3.0-0-g54eaed1d8b56b1aa528be3bdd1877e59c56fa90c"
Build-time option settings
  config.cache_oblivious: true
  config.debug: false
  config.fill: true
  config.lazy_lock: false
  config.malloc_conf: ""
  config.opt_safety_checks: false
  config.prof: false
  config.prof_libgcc: false
  config.prof_libunwind: false
  config.stats: true
  config.utrace: false
  config.xmalloc: false
Run-time option settings
  opt.abort: false
  opt.abort_conf: false
  opt.cache_oblivious: true
  opt.confirm_conf: false
  opt.retain: false
  opt.dss: "secondary"
  opt.narenas: 64
  opt.percpu_arena: "disabled"
  opt.oversize_threshold: 8388608
  opt.hpa: false
  opt.hpa_slab_max_alloc: 65536
  opt.hpa_hugification_threshold: 1992294
  opt.hpa_hugify_delay_ms: 10000
  opt.hpa_min_purge_interval_ms: 5000
  opt.hpa_dirty_mult: "0.25"
  opt.hpa_sec_nshards: 4
  opt.hpa_sec_max_alloc: 32768
  opt.hpa_sec_max_bytes: 262144
  opt.hpa_sec_bytes_after_flush: 131072
  opt.hpa_sec_batch_fill_extra: 0
  opt.metadata_thp: "disabled"
  opt.mutex_max_spin: 600
  opt.dirty_decay_ms: 10000 (arenas.dirty_decay_ms: 10000)
  opt.muzzy_decay_ms: 0 (arenas.muzzy_decay_ms: 0)
  opt.lg_extent_max_active_fit: 6
  opt.junk: "false"
  opt.zero: false
  opt.experimental_infallible_new: false
  opt.tcache: true
  opt.tcache_max: 32768
  opt.tcache_nslots_small_min: 20
  opt.tcache_nslots_small_max: 200
  opt.tcache_nslots_large: 20
  opt.lg_tcache_nslots_mul: 1
  opt.tcache_gc_incr_bytes: 65536
  opt.tcache_gc_delay_bytes: 0
  opt.lg_tcache_flush_small_div: 1
  opt.lg_tcache_flush_large_div: 1
  opt.thp: "not supported"
  opt.stats_print: true
  opt.stats_print_opts: ""
  opt.stats_print: true
  opt.stats_print_opts: ""
  opt.stats_interval: -1
  opt.stats_interval_opts: ""
  opt.zero_realloc: "alloc"
Arenas: 65
Quantum size: 16
Page size: 4096
Maximum thread-cached size class: 32768
Number of bin size classes: 36
Number of thread-cache bin size classes: 41
Number of large size classes: 196
Allocated: 38207720, active: 38789120, metadata: 4989376 (n_thp 0), resident: 44253184, mapped: 47742976, retained: 0
Count of realloc(non-null-ptr, 0) calls: 0
Background threads: 0, num_runs: 0, run_interval: 0 ns
...