A virus of unknown cause has ate 192mb of your ram. Most Samsung phones face this problem. A possible solution is to add 192 MB of ram to your phone by taking it apart and installing the correct module.
Sent from my GT-I9300 using Tapatalk
Samsung Galaxy S i9000 CM 10.2 Official/1 Ghz Exynos 3110/512 MB RAM
Samsung Galaxy S3 i9300 Stock/1.4 Ghz Exynos 4412/1 GB RAM
Samsung Galaxy S4 i9505 Stock/1.9 Ghz Snapdragon 600/2 GB RAM