Mastering Embedded Linux Programming

How much memory does my application use?

As with kernel space, the different ways of allocating, mapping and sharing user space memory make it quite difficult to answer this seemingly simple question.

To begin with, you can ask the kernel how much memory it thinks is available, which you can do by using the free command. Here is a typical example of the output:

             total     used     free   shared  buffers   cached
Mem:        509016   504312     4704        0    26456   363860
-/+ buffers/cache:   113996   395020
Swap:            0        0        0

Tip

At first sight, this looks like a system that is almost out of memory with only 4704 KiB free out of 509,016 KiB: less than 1%. However, note that 26,456 KiB is in buffers and a whopping 363,860 KiB is in cache. Linux believes that free memory is wasted memory and so ...