Get maximum memory usage of linux executable

memoryscriptingshelltime

I need a shell script which will retrieve the maximum memory consumption of a linux executable. The executable may spawn child processes using significant amounts of RAM which should be included in the total.

I've tried /usr/bin/time -f "%M" /path/to/executable, but this always yields 0 though using ps I can verify the process is indeed consuming significant RAM.

Why is time giving me 0 all the time, and how can I get the number I'm looking for?

Best Answer

I think time -f %M only works in recent Linux kernels (experimentally, it's not supported in 2.6.26/amd64, and it is supported in 2.6.32/i386).

An earlier thread at Stack Overflow didn't turn up much.

Without kernel support, monitoring memory usage is fairly hard. There are a few ways to do it:

LD_PRELOAD a small library that overloads mmap, sbrk and other memory-allocating system calls (assuming you don't run any static binaries).
ptrace the processes do watch memory allocation and forking.
Watch /proc/ (works for a single process only, and you don't know what happens between measures).

These ways all require some programming; I don't know of an existing tool.

Related Solutions

Linux – Why Red Hat Linux Reports Less Free Memory Than Available

Don't confuse free memory with unused memory. Free memory, in the unix world is a page of physical memory that has no logical data mapped to it. Unused memory does have some data mapped to it, but it is currently not in active use by a running process.

% free -m
             total       used       free     shared    buffers     cached
Mem:           997        942         55          0         71        366
-/+ buffers/cache:        504        492
Swap:         2015        618       1397

Linux (and all Unix OS'es) try to have as little free memory as possibly. Instead they use memory which is not actively mapped to processes in the running OS for things like file cache and buffers for various IO transfer operations.

Something else that may be confusing you is you cannot simply add up the memory in use by all running processes to get a total memory in use figure. If you attempted this you would quickly discover that you applications appear to be using more memory than actually exists on the machine. This is for two reasons

Memory can be shared between various processes, through Copy-On-Write memory allocation, memory mapped IO and shared dynamic libraries.
The operating system is at liberty to promise more memory to the application than it has actually supplied. The theory being that most application writers prefer to ask for large amounts of memory in one go, to avoid overhead, and may not actually use all that memory.

There is a recent article on lwn.net discussing this issue.

Linux – Memory usage of php-cgi processes is growing steadily

Try to lower down var_size. If we had value at 64MB, after a few hours it started to swap a lot, and after next few hours it was completely down. Try to keep original settings at 32M, maybe this should help you a lot - we had the same problem at our travel site Xcache is still a lot of buggy software :(

Best Answer

Related Solutions

Linux – Why Red Hat Linux Reports Less Free Memory Than Available

Linux – Memory usage of php-cgi processes is growing steadily

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