mmap 2GB allocation limit on Win XP, 32-bits, Python 2.5.4

Slaunger Slaunger at
Fri Jul 24 10:38:37 CEST 2009

OS: Win XP SP3, 32 bit
Python 2.5.4

Hi I have run into some problems with allocating numpy.memmaps
exceeding and accumulated size of about 2 GB. I have found out that
the real problem relates to numpy.memmap using mmap.mmap

I've written a small test program to illustrate it:

import itertools
import mmap
import os

files = []
mmaps = []
file_names= []
bytes_per_mmap = 100 * 1024 ** 2
    for i in itertools.count(1):
        file_name = "d:/%d.tst" % i
        f = open(file_name, "w+b")
        mm = mmap.mmap(f.fileno(), bytes_per_mmap)
        mmap_cap += bytes_per_mmap
        print "Created %d writeable mmaps containing %d MB" % (i,

#Clean up
    print "Removing mmaps..."
    for mm, f, file_name in zip(mmaps, files, file_names):
    print "Done..."

which creates this output

Created 1 writeable mmaps containing 100 MB
Created 2 writeable mmaps containing 200 MB
Created 17 writeable mmaps containing 1700 MB
Created 18 writeable mmaps containing 1800 MB
Removing mmaps...
Traceback (most recent call last):
  File "C:\svn-sandbox\research\scipy\scipy\src\com\terma\kha
\", line 16, in <module>
    mm = mmap.mmap(f.fileno(), bytes_per_mmap)
WindowsError: [Error 8] Not enough storage is available to process
this command

There is more than 25 GB of free space on drive d: at this stage.

Is it a bug or a "feature" of the 32 bit OS?

I am surprised about it as I have not found any notes about these
kinds of limitations in the documentation.

I am in dire need of these large memmaps for my task, and it is not an
option to change OS due to other constraints in the system.

Is there anything I can do about it?

Best wishes,

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