No matter what allocator Perl uses, valgrind can't detect leaked SVs (e.g. reference cycles, refcount to high) if Perl is always aware of its SVs, and that has to be the case since Perl attempts to free them during global destruction.

$ valgrind perl -e'my $x; $x = \$x; undef $x if $ARGV[0]' 1
==21363== Memcheck, a memory error detector
==21363== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et 
+al.
==21363== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h fo
+r copyright info
==21363== Command: perl -emy\ $x;\ $x\ =\ \\$x;\ undef\ $x\ if\ $ARGV[
+0] 1
==21363== 
==21363== Warning: bad signal number 0 in sigaction()
==21363== 
==21363== HEAP SUMMARY:
==21363==     in use at exit: 80,794 bytes in 609 blocks
==21363==   total heap usage: 786 allocs, 177 frees, 93,378 bytes allo
+cated
==21363== 
==21363== LEAK SUMMARY:
==21363==    definitely lost: 0 bytes in 0 blocks
==21363==    indirectly lost: 0 bytes in 0 blocks
==21363==      possibly lost: 14,538 bytes in 354 blocks
==21363==    still reachable: 66,256 bytes in 255 blocks
==21363==         suppressed: 0 bytes in 0 blocks
==21363== Rerun with --leak-check=full to see details of leaked memory
==21363== 
==21363== For counts of detected and suppressed errors, rerun with: -v
==21363== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 22 from
+ 7)

$ valgrind perl -e'my $x; $x = \$x; undef $x if $ARGV[0]' 0
==21366== Memcheck, a memory error detector
==21366== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et 
+al.
==21366== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h fo
+r copyright info
==21366== Command: perl -emy\ $x;\ $x\ =\ \\$x;\ undef\ $x\ if\ $ARGV[
+0] 0
==21366== 
==21366== Warning: bad signal number 0 in sigaction()
==21366== 
==21366== HEAP SUMMARY:
==21366==     in use at exit: 80,794 bytes in 609 blocks
==21366==   total heap usage: 786 allocs, 177 frees, 93,378 bytes allo
+cated
==21366== 
==21366== LEAK SUMMARY:
==21366==    definitely lost: 0 bytes in 0 blocks
==21366==    indirectly lost: 0 bytes in 0 blocks
==21366==      possibly lost: 14,538 bytes in 354 blocks
==21366==    still reachable: 66,256 bytes in 255 blocks
==21366==         suppressed: 0 bytes in 0 blocks
==21366== Rerun with --leak-check=full to see details of leaked memory
==21366== 
==21366== For counts of detected and suppressed errors, rerun with: -v
==21366== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 22 from
+ 7)
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