Re: why choose 896MB to the start point of ZONE_HIGHMEM

From: H. Peter Anvin
Date: Tue Apr 06 2010 - 15:53:58 EST

On 04/06/2010 12:20 PM, Frank Hu wrote:
>> The ELF ABI specifies that user space has 3 GB available to it. That
>> leaves 1 GB for the kernel. The kernel, by default, uses 128 MB for I/O
>> mapping, vmalloc, and kmap support, which leaves 896 MB for LOWMEM.
>> All of these boundaries are configurable; with PAE enabled the user
>> space boundary has to be on a 1 GB boundary.
> the VM split is also configurable when building the kernel (for 32-bit
> processors).

I did say "all these boundaries are configurable". Rather explicitly.

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