setSharedMemory.sh

#! /usr/bin/env bash

PLATFORM="`uname -sm | tr ' ' '-'`"
case "$PLATFORM" in
  Darwin-arm64) ;;
  Darwin-x86_64) ;;
	Linux-x86_64)
		echo "no need to set up shared memory"
		exit 0
     ;;
	*)
		echo "This script should only be run on Mac (Darwin-i386 or Darwin-arm64), or Linux (Linux-x86_64) ). The result from \"uname -sm\" is \"`uname -sm`\""
		exit 1
     ;;
esac

totalMem="`sysctl hw.memsize | cut -f2 -d' '`"
# Figure out the max shared memory segment size currently allowed
shmmax="`sysctl kern.sysv.shmmax | cut -f2 -d' '`"
# Figure out the max shared memory currently allowed
shmall="`sysctl kern.sysv.shmall | cut -f2 -d' '`"
totalMemMB=$(($totalMem / 1048576))
shmmaxMB=$(($shmmax / 1048576))
shmallMB=$(($shmall / 256))
# Print current values
echo "  Total memory available is $totalMemMB MB"
echo "  Max shared memory segment size is $shmmaxMB MB"
echo "  Max shared memory allowed is $shmallMB MB"

# Figure out the max shared memory segment size (shmmax) we want
# Use 75% of available memory but not more than 2GB
shmmaxNew=$(($totalMem * 3/4))
[[ $shmmaxNew -gt 2147483648 ]] && shmmaxNew=2147483648
shmmaxNewMB=$(($shmmaxNew / 1048576))

# Figure out the max shared memory allowed (shmall) we want
# The MacOSX default is 4MB, way too small
# but things will certainly break if it's been reset too small
# so ensure it's at least big enough to hold a fullsize shared memory segment
shmallNew=$(($shmmaxNew / 4096))
[[ $shmallNew -lt $shmall ]] && shmallNew=$shmall
shmallNewMB=$(($shmallNew / 256))

# Increase shmmax if appropriate
if [[ $shmmaxNew -gt $shmmax ]]; then
  echo "[Info] Increasing max shared memory segment size to $shmmaxNewMB MB"
  sudo sysctl -w kern.sysv.shmmax=$shmmaxNew
else
  echo "[Info] No need to increase max shared memory allowed"
fi

# Increase shmall if appropriate
if [ $shmallNew -gt $shmall ]; then
  echo "[Info] Increasing max shared memory allowed to $shmallNewMB MB"
  sudo sysctl -w kern.sysv.shmall=$shmallNew
else
  echo "[Info] No need to increase max shared memory allowed"
fi
# At this point, shared memory settings contain the values we want, 
# put them in sysctl.conf so they are preserved.
# Only needs to be done on OSX (see https://github.com/GsDevKit/GsDevKit_home/issues/46)
if [[ ! -f /etc/sysctl.conf || `grep -sc "kern.*m" /etc/sysctl.conf` -eq 0 ]]; then
  # On Mac OS X Leopard, you must have all five settings in sysctl.conf
  # before they will take effect.
  echo "# kern.sysv.shm* settings added by GsDevKit installation" > /tmp/sysctl.conf.$$
  sysctl kern.sysv.shmmax kern.sysv.shmall kern.sysv.shmmin kern.sysv.shmmni \
    kern.sysv.shmseg  | tr ":" "=" | tr -d " " >> /tmp/sysctl.conf.$$
  #
  echo "[Info] Adding the following section to /etc/sysctl.conf"
  cat /tmp/sysctl.conf.$$
  sudo bash -c "cat /tmp/sysctl.conf.$$ >> /etc/sysctl.conf"
  /bin/rm -f /tmp/sysctl.conf.$$
else
  echo "[Info] The following shared memory settings already exist in /etc/sysctl.conf"
  echo "To change them, remove the following lines from /etc/sysctl.conf and rerun this script"
  grep "kern.*m" /etc/sysctl.conf
fi