mstat

Print a one-line memory snapshot to STDERR. The classic marker-in-a-log tool — sprinkle mstat "Point 5" across a program to see how arena size moves between points.

mstat($marker="Devel::Peek::mstat: "). The marker prefixes the output so you can match lines to call sites when the log gets noisy. Output format is documented under perldebguts/Using $ENV{PERL_DEBUG_MSTATS}.

Only produces real numbers when Perl was built with its bundled malloc. On a standard build the line reads <marker>: perl not compiled with MYMALLOC, which is useful as a pass-through breadcrumb even when the numbers are unavailable.