How do you measure the memory usage of an application or process in Linux?
From the blog article of Understanding memory usage on Linux, ps
is not an accurate tool to use for this intent.
Why
ps
is "wrong"Depending on how you look at it,
ps
is not reporting the real memory usage of processes. What it is really doing is showing how much real memory each process would take up if it were the only process running. Of course, a typical Linux machine has several dozen processes running at any given time, which means that the VSZ and RSS numbers reported byps
are almost definitely wrong.
(Note: This question is covered here in great detail.)
You can check memory of a process or a set of processes in human readable format (in KB or kilobytes) with pmap command. All you need is the PID of the processes you want to check memory usage of. As you can see, the total memory used by the process 917 is 516104 KB or kilobytes.
It means your system is using this space to store some types of processes. Without this being cached then the system would have to create new processes frequently. Your Real Memory Usage is the actual amount of RAM usage. This should ideally be low.
With ps
or similar tools you will only get the amount of memory pages allocated by that process. This number is correct, but:
does not reflect the actual amount of memory used by the application, only the amount of memory reserved for it
can be misleading if pages are shared, for example by several threads or by using dynamically linked libraries
If you really want to know what amount of memory your application actually uses, you need to run it within a profiler. For example, Valgrind can give you insights about the amount of memory used, and, more importantly, about possible memory leaks in your program. The heap profiler tool of Valgrind is called 'massif':
Massif is a heap profiler. It performs detailed heap profiling by taking regular snapshots of a program's heap. It produces a graph showing heap usage over time, including information about which parts of the program are responsible for the most memory allocations. The graph is supplemented by a text or HTML file that includes more information for determining where the most memory is being allocated. Massif runs programs about 20x slower than normal.
As explained in the Valgrind documentation, you need to run the program through Valgrind:
valgrind --tool=massif <executable> <arguments>
Massif writes a dump of memory usage snapshots (e.g. massif.out.12345
). These provide, (1) a timeline of memory usage, (2) for each snapshot, a record of where in your program memory was allocated. A great graphical tool for analyzing these files is massif-visualizer. But I found ms_print
, a simple text-based tool shipped with Valgrind, to be of great help already.
To find memory leaks, use the (default) memcheck
tool of valgrind.
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