source: README @ 3c9fc94

memlog - A Memory-Allocation Logging Tool

This tool attempts to help you answer the question:
  Why is my application using so much memory?

** LINKING **

How to use it depends on how your application is linked:

For dynamically-linked applications, you can:

 1. Use LD_PRELOAD: Set LD_PRELOAD=/path/to/memlog/libmemlog.so when you run
    your application.

 2. Link directly: Add the following to your linker flags:
      -L/path/to/memlog -Wl,-rpath,/path/to/memlog -lmemlog

For statically-linked applications ld's automatic wrapping functionality is
employed, and the exact set of necessary flags is large, so a file named
memlog_s_ld_cmds has been provided containing the necessary flags.

To your linker flags add:

  `cat /path/to/memlog/memlog_s_ld_cmds`

or, if your compiler and wrappers support response files (gcc and clang do, for
example), simply:

  @/path/to/memlog/memlog_s_ld_cmds

so your overall linking command might look something like this:

  mpic++ -O3 -g -o my_program my_obj1.o my_obj2.o @/path/to/memlog/memlog_s_ld_cmds

** RUNNING **

When your application runs, you should find in your current directory files
named 'HOST.PID.memlog', one for each process. These contain the raw tracing
information, and are only somewhat human readable. You can create a ps/pdf
file detailing the memory allocated when each process reached its peak memory
use by running:

  /path/to/memlog/memlog_analyze /path/to/HOST.PID.memlog

this will generate files named HOST.PID.memlog.dot, HOST.PID.memlog.ps and
HOST.PID.memlog.pdf. You'll probably find the pdf file most convenient for
viewing. HOST.PID.memlog.txt is also generated, providing the same information
in textual form.

If you pass the --leaks option to memlog_analyze, it will provide data on
allocations active at the end of the program (leaks) instead of those active
when the peak memory usage is first reached.

You might have many runs of the same application (or output from many ranks of
an MPI job), and you'd like to pick the one for analysis with the highest
memory usage. If you provide a glob pattern to memlog_analyze it will do this
for you. Make sure you quote the glob pattern so that your shell does not
expand it.

  /path/to/memlog/memlog_analyze "/path/to/*.memlog"

When running under common batch systems, the files are named
JOB_ID.HOST.PID.memlog, and when running under the BG/Q CNK, the process's rank
is used instead of the node-local PID.

Note that te peak memory usage is determined by monitoring the processes's
maximum resident set size, not just the total allocated heap memory.

memlog_analyze takes, as a second optional parameter, the name of the output
directory (the current directory is the default). If the directory does not
exist, it will be created.

memlog_analyze depends on dot (from the graphviz package) and ps2pdf (from the
ghostscript package), plus various tools from the binutils package.

** RELATED WORK **

Why was memlog created? There are several other tools that can support this use
case, but none of them would work in our environment properly. They were
either too slow, not runnable under the BG/Q CNK, not thread safe, did not
properly support big-endian PPC64, supported only either static or dynamic
linking, did not collect full backtraces, or just did not produce
sufficiently-informative peak-usage output.

That having been said, some other tools that might interest you:
  Valgrind Massif - http://valgrind.org/docs/manual/ms-manual.html
  Google Performance Tools - http://google-perftools.googlecode.com/svn/trunk/doc/heapprofile.html
  memtrail - https://github.com/jrfonseca/memtrail
  LeakTracer - http://www.andreasen.org/LeakTracer/
  glibc mtrace - http://www.gnu.org/s/hello/manual/libc/Allocation-Debugging.html
  Heaptrack - http://milianw.de/blog/heaptrack-a-heap-memory-profiler-for-linux
  MemProf - http://www.secretlabs.de/projects/memprof/

The dot/pdf output produced by memlog was definitely inspired by that produced
by Google's pprof tool in the aforementioned package.