Messages in this thread | | | Date | Fri, 10 May 2002 16:58:36 +1000 | From | Anton Blanchard <> | Subject | Re: x86 question: Can a process have > 3GB memory? |
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> Huh? Unless you mean ppc64, ppc is worse. > On a Mac, you get 2 GB of virtual memory per > process. You get up to 512 MB of physical memory > without highmem support, or usually 4 GB with > highmem support.
This is fixed in recent kernels, you can specify it with a CONFIG option:
# uname -a Linux 2.4.19-pre5 #185 Fri Apr 5 14:36:40 EST 2002 ppc
# cat /proc/self/maps 0fea5000-0ffbb000 r-xp 00000000 03:0c 163581 /lib/libc-2.2.5.so 0ffbb000-0ffc5000 ---p 00116000 03:0c 163581 /lib/libc-2.2.5.so 0ffc5000-0ffeb000 rw-p 00110000 03:0c 163581 /lib/libc-2.2.5.so 0ffeb000-0fff0000 rw-p 00000000 00:00 0 10000000-10003000 r-xp 00000000 03:0c 1554092 /bin/cat 10012000-10013000 rw-p 00002000 03:0c 1554092 /bin/cat 10013000-10015000 rwxp 00000000 00:00 0 48000000-48014000 r-xp 00000000 03:0c 163537 /lib/ld-2.2.5.so 48014000-48015000 rw-p 00000000 00:00 0 48023000-48027000 rw-p 00013000 03:0c 163537 /lib/ld-2.2.5.so bfffe000-c0000000 rwxp fffff000 00:00 0
Of course on ppc64 kernels you have a full 4GB of userspace since the kernel sits at the top of the 64bit address space.
> As with x86, the latest chips > offer a 36-bit (64 GB) physical address space.
Paulus also has a hack that allows up to 15G of memory on POWER3 class machines although that isnt currently in the ppc32 tree.
> That's not all! Linus recently singled out the PowerPC > MMU for a nice long abusive rant. :-) You get hashed > page tables. You get this: > > As with x86, segment registers map a 32-bit virtual > address space onto a larger one. The top 4 bits of > a 32-bit virtual address are used to select a segment, > and the segment provides 24 more address bits to > give you a 52-bit virtual address. Eeeew.
This is all very well and good, put my ppc64 machine still outperforms anything out there on the kernel compile benchmark :)
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