```{index} single: mstat; Devel::Peek function ``` ```{index} single: Devel::Peek::mstat; Perl function ``` # 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 `: perl not compiled with MYMALLOC`, which is useful as a pass-through breadcrumb even when the numbers are unavailable.