Out of memory here  with a testfile of  662M
Linux 32bit, 4GByte, PAE extension

# time ./read_blocks.lua

real    0m2.458s
user    0m0.372s
sys    0m1.084s
# time ./read_whole_file.lua
not enough memory

real    0m17.125s
user    0m11.737s
sys    0m4.292s

# texlua -v
This is LuaTeX, Version beta-0.70.1-2012052416 (rev 4277)

Indeed not enough mem on my laptop for a 600M+ test.

Windows 8, 32 bit:

-- all      1.082   34176584    120272.328125
-- chunked  0.668   34176584    169908.59667969
-- once     1.065   34176584    111757.03710938

-- all      7.078   136706337   535063.34863281
-- chunked  3.441   136706337   787195.56933594
-- once     6.621   136706337   501559.83691406

the larger values for 'all' and 'once' still puzzle me.