Michael Green wrote:
How one can tell how much precisely physical memory is free on a given system.
You can either look at /proc/meminfo (cat /proc/meminfo), or use the tool "top". Note though at any given time, you'll probably see that nearly all of your physical is used, as the kernel, roughly speaking, uses any spare memory for caching data from the disk. Perhaps (Memtotal-Cached) is an estimate of your actual used memory by running processes (others may correct me here).
Another question is how a group of users can be limited in terms of memory. I have a system here that's starved by IO and I want ot prevent users jobs allocating big chunks of swap. say if I have a Linux system with 2G of RAM and 4G of swap is it possible to allocate to a _group_ of users 1700M only?
Here I think you could look at man ulimit. This allows you to limit the resources available to each process. I guess you could sort of do what you want by limiting things like limiting a processes data segment (ulimit -d), maximum size that may be locked into memory (ulimit -l), the maximum stack size (ulimit -s), and the maximum amount of virtual memory (swap) available to the shell (ulimit -v). I'm not entirely sure how this could help you set limits for a group, though.
HTH Jonathan
