Note that because you don't use "my" here, all these variables will stay in memory even after the loop has finished.

That happens when using my too. Neither the SV nor the string buffer are freed. They are simply cleared.

Update: The following isn't proof, but it does let you see the effect of what I described. 

use Devel::Peek qw( Dump );

sub foo {
   my ($x) = @_;
   undef($x) if !@_;
   Dump($x);
}


foo("abc");
foo("defghijkl");
foo("mno");
foo(undef);  # $x = undef
foo();       # undef $x
foo("pqr");

[download]

Pay particular attention to LEN, the allocated length of the string buffer associated with the variable. 

SV = PV(0x22612c) at 0x22606c
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,POK,pPOK)
  PV = 0x22f4d4 "abc"\0
  CUR = 3
  LEN = 4
SV = PV(0x22612c) at 0x22606c       Could be coincidence, but isn't.
  REFCNT = 1                          The SV wasn't freed.
  FLAGS = (PADBUSY,PADMY,POK,pPOK)
  PV = 0x182cadc "defghijkl"\0      New larger (LEN=12) str buf.
  CUR = 9
  LEN = 12
SV = PV(0x22612c) at 0x22606c
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,POK,pPOK)
  PV = 0x182cadc "mno"\0            Same "large" (LEN=12) buf reused.
  CUR = 3
  LEN = 12
SV = PV(0x22612c) at 0x22606c
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY)           Undefined
  PV = 0x182cadc "mno"\0            Str buf untouched.
  CUR = 3
  LEN = 12
SV = PV(0x22612c) at 0x22606c
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY)           Undefined
  PV = 0                            Str buf freed.
SV = PV(0x22612c) at 0x22606c
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,POK,pPOK)
  PV = 0x22f4d4 "pqr"\0             New small (LEN=4) str buf.
  CUR = 3                             Same address as earlier
  LEN = 4                             is a coincidence.

[download]

In reply to Re^2: out of memory problem by ikegami
in thread out of memory problem by lightoverhead

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