2GB address space limit on 32-bit PowerPC Macintosh

John Reiser jreiser at BitWagon.com
Mon May 16 08:36:54 EST 2005

The 2GB limit on TASK_SIZE for user address space on 32-bit PowerPC
Apple Macintosh is getting in the way of database, filesystem
maintenance, and scientific applications.  In user mode, most
i686 desktops can address 3GB.  While 64-bit systems are becoming
available, the vast majority of existing systems are still 32-bit.
What can be done to get a larger address space for existing Macs?

According to arch/ppc/syslib/prom_init.c, the first problem is
that CONFIG_BOOTX_TEXT restricts CONFIG_TASK_SIZE to only 0x80000000.
Is this an initialization-only restriction that just happens
to persist beyond initialization?  What would it take to remove
this collision from affecting life after boot?  How much of booting
does CONFIG_BOOTX_TEXT affect?


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