This is a DTrace script for Ruby 2.0 that profiles object allocations.

allocations.d

#pragma D option dynvarsize=100m

dtrace:::BEGIN
{
	self->depth = 0;
}

ruby*:::method-entry
{
	self->depth++;
	self->classes[self->depth] = copyinstr(arg0);
	self->methods[self->depth] = copyinstr(arg1);
}

ruby*:::method-return
{
	self->depth--;
}

ruby*:::object-create
{
	@allocations[self->classes[self->depth], self->methods[self->depth], copyinstr(arg0)] = count();
}

dtrace:::END
{
	printf("\n\n");
	printf("---------------------------------------- ---------------------------------------- ---------------------------------------- -------\n");
	printf("%-40s %-40s %-40s %s\n", "CALLER CLASS", "CALLER METHOD", "ALLOCATED CLASS", "COUNT");
	printf("---------------------------------------- ---------------------------------------- ---------------------------------------- -------\n");
	printa("%-40s %-40s %-40s %@d\n", @allocations);
	printf("---------------------------------------- ---------------------------------------- ---------------------------------------- -------\n");
}

log.txt

------------------------------ ------------------------------ ------------------------------ -------
CALLER CLASS                   CALLER METHOD                  ALLOCATED CLASS                COUNT
------------------------------ ------------------------------ ------------------------------ -------
                                                              #<Class:0x007f89e18e0720>      1
                                                              ARGF.class                     1
                                                              Foo                            1
                                                              Gem::Version                   1
                                                              IOError                        1
                                                              Mutex                          1
                                                              NoMemoryError                  1
                                                              SystemStackError               1
                                                              ThreadGroup                    1
                                                              Time                           1
Gem::Requirement               parse                          Gem::Version                   1
Gem::Specification             unresolved_deps                Hash                           1
                                                              Hash                           2
                                                              LoadError                      2
                                                              Object                         2
Gem::Requirement               default                        Gem::Requirement               2
Gem::Specification             initialize                     Hash                           8
Gem::Specification             load                           Gem::Specification             8
Gem::Specification             load                           String                         8
Gem::Version                   create                         Gem::Version                   8
Gem::Version                   initialize                     String                         10
Gem::Specification             initialize                     Gem::Requirement               21
Gem::Specification             initialize                     String                         24
Gem::Specification             initialize                     Array                          96
Foo                            initialize                     Bob                            100
Foo                            initialize                     String                         100
                                                              String                         218
------------------------------ ------------------------------ ------------------------------ -------