I am using System Monitor 2.28.0. When I look in the Resources tab, I see a nice graph with for memory and swap. Memory is about 60% 2.3 GiB of 3.8. When I type the command free, I got :
total used free shared buffers cached Mem: 3994908 3962396 32512 0 100852 1477032 -/+ buffers/cache: 2384512 1610396 Swap: 8000328 28468 7971860
cat /proc/meminfo | grep MemFree give
MemFree: 34536 kB
The situation has remained the save for several minute. I started a lot of process with a script and the script is waiting for the free memory to get lower. According to what I am seeing in the Process tab (or with top), the number in System Monitor seem a lot closed to the total of the memory of the process that the one reported by free.