Linux shared memory segment access problem and x86 Virtual Memory layout.

regmee · 08-22-2008, 05:40 PM

Hi all,

I have been trying to attach a shared memory segment in a 32-bit x86 machine in the virtual address range ( 0xff80 0000 to 0xffff ffff ) with no luck.

Code:

  0xffff ffff+-----------------+  (4096 MB) 4 GB
             |   Problem :(    |
  0xff80 0000+-----------------+  (4088 MB)  
             |                 |
             |                 |
             |                 |
  0x7fff ffff+-----------------+
             |                 |
             |                 |
             |                 |
  0x7f80 0000+-----------------+
             |                 |
             |                 |
             |                 |
  0x0000 0000+-----------------+

This definitely falls in the upper 1 GB address space which belongs to the Kernel.

Is there any way by which I can attach a shared memory segment to one of those addresses in that zone ???

I tried increasing the SHMMAX value to as high as 4 GB. Din't help.

Eventually I will have to attach similarly for an x86_64 architecture. Please let me know if my problem has a solution and the same approach can be applied for a x86_64 architecture that uses canonical form of virtual addresses.

Regards,
Regmee

Valery Reznic · 08-23-2008, 12:11 AM

Could you explain what you are trying to achieve ?