The problem comes when you need to build a list of indexes as with the OPs code:

sub checkMem{ `tasklist /nh /fi "pid eq $_[0]"`; };;

print checkMem( $$ );;
 perl.exe                      3040 Console                    1      
+9,544 K

$#a = 1e6;;
print checkMem( $$ );;
 perl.exe                      3040 Console                    1     1
+7,428 K

map{ $_ } 0 .. $#a;;
print checkMem( $$ );;
 perl.exe                      1224 Console                    1     7
+3,272 K           ### 56MB to build the list of 1e6 indices ###
[download]