The automatically generated description above is taken from the manual page of the /proc filesystem under Linux and is a little bit confusing, so I make this clear here. Well, every operating system has its own idea about the memory usage of a processes, and also system utilities like ps show different things on different systems. Nevertheless, we should try to make &libgtop; as system independent as possible, so I give you some hints here how &glibtop-get-procmem; should work. When you use &mmap; with either &MAP-SHARED; or &MAP-PRIVATE;, this should only affect the &pmem-vsize; of the process and none of its &pmem-size;, &pmem-resident;, &pmem-shared; and &pmem-rss; sizes. As soon as you read some of the &mmap;ed pages, they will be demand-loaded and thus count towards the &pmem-size; of the process. Also - we assume there is enough free memory - they are resident in memory until they get stolen or swapped out and thus increase the &pmem-resident; and &pmem-rss; sizes of the process. If the process has used &MAP-SHARED; and another process attaches the same file also &MAP-SHARED; some of the pages are shared with this process and thus increase the &pmem-shared; sizes of both processes. If the process has used &MAP-PRIVATE; and writes to the &mmap;ed pages, the only difference to reading from them is that they get dirty and cannot be stolen any longer but will get swapped out. If memory gets rare, clean pages are normally stolen which decreases the &pmem-size;, &pmem-resident;, &pmem-shared; and &pmem-rss; sizes of the process. When dirty pages are swapped out, this will not decrease the &pmem-size; of the process but only its &pmem-resident; and &pmem-rss; sizes (dirty pages cannot be shared). The &pmem-vsize; of a process can only be changed by the process itself when it requests or frees memory but never due to swapping activity of the system. If the &pmem-shared; size changes, this only means that the number of pages that are currently shared with other processes has changed; if this happens, this will never affect any of the other sizes of the process. The hints above describe how it works under Linux - and we should try to make &glibtop-get-procmem; show the same behavior under every other system. If you want to make any comments, flames, suggestions about this, please feel free to do so.