Massive disk i/o on memory reach %70

Question

Previously system became unresponsive when RAM usage reached around %70. It was because of massive disk I/O operation, presumably to swap disk. I tried to tweak swapiness factor and it didn't affect anything at all on both sides of the extreme. I decided to delete the swap partition altogether, since my system has 4GB RAM. The swap partition was about 6GB. It is yet no difference. It seems in whatsoever configuration, %30 of memory should always be free. This is not a space rocket command and control system, so I don't understand this cautious policy. Can anyone please explain? Is there any other setting I could tweak to get the bar of memory usage up to say %95?

Thanks

Answer 1

Linux uses all unused RAM for disk cache ('cached' value in free). As more RAM is used by applications the less RAM is available for caching disk activities. So if your system has high I/O throughput on recurring files it has to read the same files again and again when most of the RAM is used by applications which will make it unresponsive.