Linux: How to measure actual memory usage of an application or process?

Question

Hi,

How do you measure the memory usage of an application or process in Linux? I've read here that "ps" is not an accurate tool to use for this intent.

Thanks, Kenneth

Answer 1

With ps or similiar tools you will only get the amount of memory pages allocated by that process. This number is correct, but:

a) does not reflect the actual amount of memory used by the application, only the amount of memory reserved for it

b) 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.

Answer 2

Hard to tell for sure, but here are two "close" things that can help.

$ ps aux 

will give you Virtual Size (VSZ)

You can also get detailed stats from /proc filesystem by going to /proc/$pid/status

The most important is the VmSize, which should be close to what "ps aux" gives.

/proc/19420$ cat status
Name:   firefox
State:  S (sleeping)
Tgid:   19420
Pid:    19420
PPid:   1
TracerPid:  0
Uid:    1000 1000 1000 1000
Gid:    1000 1000 1000 1000
FDSize: 256
Groups: 4 6 20 24 25 29 30 44 46 107 109 115 124 1000 
VmPeak:   222956 kB
VmSize:   212520 kB
VmLck:         0 kB
VmHWM:    127912 kB
VmRSS:    118768 kB
VmData:   170180 kB
VmStk:       228 kB
VmExe:        28 kB
VmLib:     35424 kB
VmPTE:       184 kB
Threads:    8
SigQ:   0/16382
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000020001000
SigCgt: 000000018000442f
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
Cpus_allowed:   03
Mems_allowed:   1
voluntary_ctxt_switches:    63422
nonvoluntary_ctxt_switches: 7171

Answer 3

Get valgrind. give it your program to run, and it'll tell you plenty about its memory usage.

This would apply only for the case of a program that runs for some time and stops. I don't know if valgrind can get its hands on an already-running process or shouldn't-stop processes such as daemons.

Answer 4

Another vote for valgrind ("VAL-grinned")! Fantastic tool, IMHO.

Website here

Answer 5

There is no easy way to calculate this. But some people have tried to get some good answers: ps_mem.py

Answer 6

I use top to monitor the program, but will try valgrind to confirm it's usefulness

Answer 7

Another vote for Valgrind here, but I would like to add that you can use a tool like Alleyoop to help you interpret the results generated by valgrind.

I use the two tools all the time and always have lean, non-leaky code to proudly show for it ;)

Answer 8

There isn't a single answer for this because you can't pin point precisely the amount of memory a process uses. Most processes under linux use shared libraries. For instance, let's say you want to calculate memory usage for the 'ls' process. Do you count only the memory used by the executable 'ls' ( if you could isolate it) ? How about libc? Or all these other libs that are required to run 'ls'?

linux-gate.so.1 =>  (0x00ccb000)
librt.so.1 => /lib/librt.so.1 (0x06bc7000)
libacl.so.1 => /lib/libacl.so.1 (0x00230000)
libselinux.so.1 => /lib/libselinux.so.1 (0x00162000)
libc.so.6 => /lib/libc.so.6 (0x00b40000)
libpthread.so.0 => /lib/libpthread.so.0 (0x00cb4000)
/lib/ld-linux.so.2 (0x00b1d000)
libattr.so.1 => /lib/libattr.so.1 (0x00229000)
libdl.so.2 => /lib/libdl.so.2 (0x00cae000)
libsepol.so.1 => /lib/libsepol.so.1 (0x0011a000)

You could argue that they are shared by other processes, but 'ls' can't be run on the system without them being loaded.

Also, if you need to know how much memory a process needs in order to do capacity planning, you have to calculate how much each additional copy of the process uses. I think /proc/PID/status might give you enough info of the memory usage AT a single time. On the other hand, valgrind will give you a better profile of the memory usage throughout the lifetime of the program

Answer 9

Valgrind is amazing if you have the time to run it. valgrind --tool=massif is The Right Solution.

However, I'm starting to run larger examples, and using valgrind is no longer practical. Is there a way to tell the maximum memory usage (modulo page size and shared pages) of a program?

On a real unix system, /usr/bin/time -v works. On linux, however, this does /not/ work.

Answer 10

In recent versions of linux, use the smaps subsystem. For example, for a process with a PID of 1234:

cat /proc/1234/smaps

It will tell you exactly how much memory it is using at that time. More importantly, it will divide the memory into private and shared, so you can tell how much memory your instance of the program is using, without including memory shared between multiple instances of the program.

Answer 11

If you want something quicker than profiling with Valgrind and your kernel is older and you can't use smaps, a ps with the options to show the resident set of the process (with "ps -o rss,command") can give you a quick and reasonable aproximation of the real amount of non-swapped memory being used.

Answer 12

This is an excellent summary of the tools and problems: http://ktown.kde.org/~seli/memory/analysis.html

I'll quote it, so that more devs will actually read it.

If you want to analyse memory usage of the whole system or to thoroughly analyse memory usage of one application (not just its heap usage), use exmap. For whole system analysis, find processes with the highest effective usage, they take the most memory in practice, find processes with the highest writable usage, they create the most data (and therefore possibly leak or are very ineffective in their data usage). Select such application and analyse its mappings in the second listview. See exmap section for more details. Also use xrestop to check high usage of X resources, especially if the process of the X server takes a lot of memory. See xrestop section for details.

If you want to detect leaks, use valgrind or possibly kmtrace.

If you want to analyse heap (malloc etc.) usage of an application, either run it in memprof or with kmtrace, profile the application and search the function call tree for biggest allocations. See their sections for more details.

Answer 13

Valgrind can show detailed information but it slows down the target application significantly, and most of the time it changes the behavior of the app. Exmap was something I didn't know yet, but it seems that you need a kernel module to get the information, which can be an obstacle.

I assume what everyone wants to know WRT "memory usage" is the following...
In linux, the amount of physical memory a single process might use can be roughly divided into following categories.

• M.a anonymous mapped memory
  • .p private
    • .d dirty == malloc/mmapped heap and stack allocated and written memory
    • .c clean == malloc/mmapped heap and stack memory once allocated, written, then freed, but not reclaimed yet
  • .s shared
    • .d dirty == there should be none
    • .c clean == there should be none
• M.n named mapped memory
  • .p private
    • .d dirty == file mmapped written memory private
    • .c clean == mapped program/library text private mapped
  • .s shared
    • .d dirty == file mmapped written memory shared
    • .c clean == mapped library text shared mapped

I would prefer to get the numbers as follows to get the real numbers in least overhead.
You have to sum these up in order to divide what ps shows as RSS and get more accurate numbers not to confuse.
/proc//status tries to show these numbers, but they are failing.
So instead of trying to label [anon], [stack], correctly to each mapping, my wish is that linux kernel people will mainline the proc entry code to sum and show these M.a.p.d, M.a.p.c, M.n.p.d, .... numbers.
Embedded linux people will get really happy IMHO.

M.a.p.d:

 awk '/^[0-9a-f]/{if ($6=="") {anon=1}else{anon=0}} /Private_Dirty/{if(anon) {asum+=$2}else{nasum+=$2}} END{printf "sum=%d\n",asum}' /proc/<pid>/smaps

M.a.p.c:

 awk '/^[0-9a-f]/{if ($6=="") {anon=1}else{anon=0}} /Private_Clean/{if(anon) {asum+=$2}else{nasum+=$2}} END{printf "sum=%d\n",asum}' /proc/<pid>/smaps

M.n.p.d:... and so on

Answer 14

pmap -x

Answer 15

If your code is in C or C++ you might be able to use getrusage() which returns you various statistics about memory and time usage of your process.

Not all platforms support this though and will return 0 values for the memory-use options.

Instead you can look at the virtual file created in /proc/[pid]/statm (where [pid] is replaced by your process id. You can obtain this from getprocessid()).

This file will look like a text file with 7 integers. You are probably most interested in the first (all memory use) and sixth (data memory use) numbers in this file.