The three x expressions are constant folded at compile time

Nice theory... but if the size to allocate isn't known before run-time, you still do get the same behavior.  Even in slightly modified cases like these, where the $y should definitely go out of scope (and thus the memory behind it be available for reuse): 

$ strace -e mmap,munmap perl -e '$n=2**20; $x="x" x $n; {my $y=$x}{my 
+$y=$x}{my $y=$x}'
...
mmap(NULL, 1052672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -
+1, 0) = 0x7fa5d43d3000
mmap(NULL, 1052672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -
+1, 0) = 0x7fa5d2ecd000
mmap(NULL, 1052672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -
+1, 0) = 0x7fa5d2dcc000
mmap(NULL, 1052672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -
+1, 0) = 0x7fa5d2ccb000
mmap(NULL, 1052672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -
+1, 0) = 0x7fa5d2bca000
munmap(0x7fa5d2bca000, 1052672)         = 0
munmap(0x7fa5d2ccb000, 1052672)         = 0
munmap(0x7fa5d2dcc000, 1052672)         = 0
munmap(0x7fa5d43d3000, 1052672)         = 0

[download]

Personally, I'd consider this a bug.

Note that if you write for (1..3) {my $y = $x} instead of spelling out {my $y = $x} three times, the memory is being reused just fine: 

$ strace -e mmap,munmap perl -e '$n=2**20; $x="x" x $n; for (1..3) {my
+ $y=$x}'
...
mmap(NULL, 1052672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -
+1, 0) = 0x7f9d9bdfd000
mmap(NULL, 1052672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -
+1, 0) = 0x7f9d9a8f7000
mmap(NULL, 1052672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -
+1, 0) = 0x7f9d9a7f6000
munmap(0x7f9d9a7f6000, 1052672)         = 0
munmap(0x7f9d9bdfd000, 1052672)         = 0

[download]

In reply to Re^2: Freeing memory, revisited (Linux) by Eliya
in thread Freeing memory, revisited (Linux) by lkundrak

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