This setting is hidden inside system settings. This memory is used when the system runs out of RAM, so the more you have, the better. Your virtual memory should be double your actual RAM.
10GB is fine if you are playing only one Game. I recommend 16GB as a good standard if you are going to play more than two games. Make sure you give it enough space for running the game. Even after using my PUBG Mobile Optizmation guide I recommend giving it at least 4GB of RAM for smooth gameplay. Give LD Player all the RAM you have! Running games like PUBG need a lot of RAM.
You should not be using other apps while using LD Player as it will degrade the performance of the LD player. Set it the same as your CPU Cores so that you can get the best performance. Otherwise, you will experience a blurry gameplay experience on LD Player.