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问题:
I am using the following code to get the max memory usage of the program.
import os, subprocess , psutil def mem(cmd): try: with open('in.txt','r') as infile, open('out.txt', 'w') as outfile: p=psutil.Popen("./"+cmd,shell=False,stdin=infile,stdout = outfile) print p.memory_info() except Exception: print "Error" cmd=raw_input() mem(cmd)
The problem is sometimes for initial runs of the program the memory usage output is (0,0) but subsequently it displays the correct output. I dont why this happening. For some programs such as the hello world program in c++ the output is pmem(rss=4096, vms=315392) which is about 0.3M( I think the output is in bytes ) but running the hello world program in ideone.com gives the output as ~3M. Why is there this disperency?
cmd is the name of the executable.
The output of command print subprocess.check_output(['ps', 'v', '-p', str(p.pid)])
PID TTY STAT TIME MAJFL TRS DRS RSS %MEM COMMAND 16150 pts/16 Z+ 0:00 0 0 0 0 0.0 [a.out]
One of my sample C++ program:
`int a[1000000]; int main() { return 0; }`
returns pmem(rss=4096, vms=4313088) sometimes and pmem(rss=0,vms=0) sometimes
回答1:
p.poll() or p.wait())). It seems both psutil and ps shows RSS to be zero for such processes.
The result depends on whether the subprocess will exit sooner than p.memory_info() is called. It is a race. If you add a delay at the exit in the C++ program then p.memory_info() may be called before the subprocess exits and you should get non-zero results.
The problem is that I can get arbitrary programs to evaluate . The language is also not fixed. Isn't there an elegant solution to this problem?
You might need OS support to save info about the memory usage by a subprocess even after it exits. Or you could run the program using a memory profiler such as valgrind and read its results. To collect results:
$ valgrind --tool=massif cmd arg1 arg2
To see the results, you could use ms_print:
$ ms_print massif.out.* | less
Or GUI Massif-Visualizer
@mdadm suggested a simpler solution: time command:
from subprocess import Popen, PIPE p = Popen(['time', '-f', '%M'] + args, stderr=PIPE) ru_maxrss = int(p.communicate()[1]) print("Maximum rss %d KB" % ru_maxrss)
GNU time uses wait3() to populate resource usage info if it is available. It can be called in Python:
import os from subprocess import Popen p = Popen(args) ru = os.wait4(p.pid, 0)[2] print("Maximum rss %d KB" % ru.ru_maxrss)
I've compared the maximum value returned by psutil.Process.memory_info (rss) with ru_maxrss value returned by os.wait4 and with the maximum total memory reported by valgrind --tool=massif: they are similar.
See also:
回答2:
The problem here is that psutils takes a quick snapshot from the /proc filesystem, as you can see in the source.
When you run your hello world example, in some cases it finishes before python gets a chance to read the values from /proc.
Once the process is finished, it effectively no longer consumes any ram. You can confirm this with an strace.
open("/proc/13420/statm", O_RDONLY) = 3 read(3, "0 0 0 0 0 0 0\n", 1024) = 14
If you modify your example to use something like sleep, you'll notice that psutils consistently gives memory usage back.
#include #include int main() { std::cout
Output of your python script...
a.out meminfo(rss=286720, vms=12931072)
One simple way to accomplish what you are trying to do, is by using the /usr/bin/time command, which on most platforms will give you the average total memory usage of the process you launch OR use valgrind as J.F Sebastian suggests... whom posted as I was researching and testing my answer ;)
Hello World.. sleeping!0.00user 0.00system 0:03.00elapsed 0%CPU (0avgtext+0avgdata 1144maxresident)k 0inputs+0outputs (0major+348minor)pagefaults 0swaps
