Consult sv.c about the arenas. This is where everything perl manages is managed. You'll write some C which can be used by the visit() function. That function can find your SV heads where SvANY() == your pointer. I'd guess you'd zero the refcount and call sv_clear on it then. I've included a copy of a simple function that uses visit() just so you can see how short and easy this can be.

    visit(do_report_used, 0, 0);

static void
do_report_used(pTHX_ SV *sv)
{
    if (SvTYPE(sv) != SVTYPEMASK) {
        PerlIO_printf(Perl_debug_log, "****\n");
        sv_dump(sv);
    }
}
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