Devel::Leak has two functions 'NoteSV' and 'CheckSV'.

'NoteSV' walks the perl internal table of allocated SVs (scalar values) -
(which actually contains arrays and hashes too), and records their
addresses in a table. It returns a count of these "things", and stores a
pointer to the table (which is obtained from the heap using malloc()) in
its argument.

'CheckSV' is passed argument which holds a pointer to a table created by
'NoteSV'. It re-walks the perl-internals and calls sv_dump() for any
"things" which did not exist when 'NoteSV' was called. It returns a count
of the number of "things" now allocated.