mwrap - LD_PRELOAD malloc wrapper + line stats for Ruby

mwrap is designed to answer the question:

Which lines of Ruby are hitting malloc the most?

mwrap wraps all malloc, calloc, and realloc calls to trace the Ruby source location of such calls and bytes allocated at each callsite. This functionality may be expanded in the future.

It does not track allocation lifetimes, or frees, however. It works best for allocations under GVL, but tries to track numeric caller addresses for allocations made without GVL so you can get an idea of how much memory usage certain extensions and native libraries use.

It requires the concurrent lock-free hash table from the Userspace RCU project: liburcu.org/

It does not require recompiling or rebuilding Ruby, but only supports Ruby trunk (2.6.0dev+) on a few platforms:

  • GNU/Linux

  • FreeBSD (tested 11.1)

It may work on NetBSD, OpenBSD and DragonFly BSD.

Install

# FreeBSD: pkg install liburcu

# Debian-based systems: apt-get liburcu-dev

# Install mwrap via RubyGems.org gem install mwrap

Usage

mwrap works as an LD_PRELOAD and supplies a mwrap RubyGem executable to improve ease-of-use. You can set dump_fd: in the MWRAP environment variable to dump the results to a certain file descriptor at exit:

# Dump results to stderr at exit: MWRAP=dump_fd:2 mwrap RUBY_COMMAND

You may also set dump_path to append to a log file:

MWRAP=dump_path:/path/to/log mwrap RUBY_COMMAND

You may also ‘require ’mwrap” in your Ruby code and use Mwrap.dump, Mwrap.clear, Mwrap.reset, Mwrap.each, etc.

However, mwrap MUST be loaded via LD_PRELOAD to have any effect in tracking malloc use.

The output of the mwrap dump is a text file with 3 columns:

total_bytes call_count location

Where location is a Ruby source location (if made under GVL) or an address retrieved by backtrace_symbols(3)

Known problems

  • 32-bit machines are prone to overflow (WONTFIX)

Mail archives and list:

80x24.org/mwrap-public/ nntp://80x24.org/inbox.comp.lang.ruby.mwrap

No subscription will ever be required to post, but HTML mail will be rejected:

[email protected]

Hacking

git clone 80x24.org/mwrap.git

Send all patches and pull requests (use “git request-pull” to format) to the mailing list. We do not use centralized or proprietary messaging systems.

License

GPL-2.0+ <www.gnu.org/licenses/gpl-2.0.txt>