Messages in this thread | | | From | "Albert D. Cahalan" <> | Subject | Re: x86 question: Can a process have > 3GB memory? | Date | Thu, 9 May 2002 19:56:29 -0400 (EDT) |
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Robert Love writes: > On Thu, 2002-05-09 at 14:24, tchiwam wrote:
>> How about other architectures ? like PowerPc. >> Last calculation I did used 11GB of ram (no swap) on a big Number >> Muncher... Would it be nice to use the same code for testing on 32 >> architectures with swap ? > > All 32-bit architectures have a 4GB address space, 64-bit architectures > obviously have a much bigger one (depends on the arch how many bits are > used for the address space). > > PPC obviously does not have the dumb physical memory limitations x86 > has, however.
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. As with x86, the latest chips offer a 36-bit (64 GB) physical address space.
Virtual memory layout:
00000000-7fffffff user 80000000-bfffffff waste (for IO on obscure Amiga "upgrade" junk) c0000000-dfffffff non-paged mapping of 512 MB at phys addr 0 e0000000-ffffffff IO, vmalloc(), etc.
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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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