I've found the following to be true on my system and feel these details
could usefully be added to the Changing Cygwin's Maximum Memory page in
the User's Guide. My system is a Dell Inspiron 1520 laptop with 4GB of
physical RAM running Windows XP Home Edition with SP3. Uname -v reports
the Cygwin Kernel version as 2010-04-07 11:02 Some of these comments
are specific to XP; I gather Vista does not use a boot.ini file, for
example. Perhaps others running other operating systems could flesh it
out to provide complete documentation across operating systems.
1) When changing the maximum memory available to Cygwin using "regtool
-i set /HKLM/Software/Cygwin/heap_chunk_in_mb MMMM" the maximum useful
value of MMMM is 4095. Values of 4096 and above result in the heap size
reverting to its unset value (about 1000 on my system).
2) With this change in place processes are still limited to 2GB of
memory on 32-bit Windows systems, unless you set the /3GB switch in your
boot.ini file. This switch allows each process to grow to 3GB.
However, used alone it may have undesirable consequences (such as your
system hanging) which the /Userva=MMMM flag may prevent. MMMM from 2900
to 3030 is recommended. This switch caps user processes at MMMM MB.
The change might be from a boot.ini file of
[boot loader]
;timeout=30
default=multi(0)disk(0)rdisk(0)partition(2)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Home
Edition" /noexecute=optin /fastdetect
to
[boot loader]
;timeout=30
default=multi(0)disk(0)rdisk(0)partition(2)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Home
Edition" /noexecute=optin /fastdetect
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Home
Edition 2.83GB" /3GB /Userva=2900 /noexecute=optin /fastdetect
You should then get a choice between OS configurations at boot. If you
use a 3rd party boot loader you may have to make the configuration
changes there instead of directly to the boot.ini file.
3) With both these changes in place your process will STILL be limited
to 2GB process size, unless you compile it with the /LARGEADDRESSAWARE
linker flag in place. Under gcc this flag is specified thus : gcc
-Wl,--large-address-aware -o program.x program.c That's W ell, not W one.
With all these changes in place I can now run gcc compiled Cygwin
processes up to 2.83GB in size :)
/rob
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