Is it possible in Java 8 to set the memory limit based on system memory and not java process memory?

Question

linux

For example, if 95% is busy - do a dump and crash
Example - there is an instance with 4 GB of RAM and 2 java processes are running. And I want 2 processes to use all the memory, but if the system memory runs out, then kill the process and make a dump.
If I use -Xmx4g, then both consider that they can use 4GB and in total they can eat 8 GB and go into swap. if I write -Xmx2g, then both will fit, but if one process uses all 2 GB, then the second cannot use this memory.

Answer 1

In your case, there is no pure java solution. Here you need to charge a regular task (cron), which will look at the free physical memory in the system and kill the fattest java application when it reaches 95% of the memory limit. For example, like this:

#!/usr/bin/env bash

# pid'ы отслеживаемых java процессов
# задачку определения актуальных pid'ов оставлю на вас
PID1=1234
PID2=5678

# минимальное допустимое количество свободной памяти в процентах
MIN_MEM_SIZE=5

function get_java_mem {
  jstat -gc $1 | awk 'NR==1 {print ($3 + $4 + $6 + $8 + $10)}'
}

function get_free_mem {
  free | awk 'NR==2 {print ($7 * 100) / $2}'
}

if [ $(echo "`get_free_mem` < $MIN_MEM_SIZE" | bc) -eq "1" ]; then
  if [ $(echo "`get_java_mem $PID1` > `get_java_mem $PID2`" | bc) -eq "1" ]; then
    PID_TO_KILL=$PID1;
  else
    PID_TO_KILL=$PID2
  fi
  echo "Memory shortage detected. Taking heap dump and killing process $PID_TO_KILL"
  jmap  -dump:format=b,file=${PID_TO_KILL}.heapdump.bin $PID_TO_KILL
  kill $PID_TO_KILL
fi

if I write -Xmx2g, then both will fit, but if one process uses all 2 GB, then the second cannot use this memory.

It is not very clear why such a swing is needed. If the application works fine with -Xmx2g, then with -Xmx4g it will not get much better. Unless full gc will happen a little more often, that's all.

Answer 2

No.