Messages in this thread | | | Date | Tue, 6 Apr 2010 13:15:49 -0700 | Subject | Re: why choose 896MB to the start point of ZONE_HIGHMEM | From | Frank Hu <> |
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On Tue, Apr 6, 2010 at 12:44 PM, H. Peter Anvin <hpa@zytor.com> wrote: > 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. > > -hpa >
thought that you can only configure how to split the VM like 1G/3G or 2G/2G. But the DMA zone size, the 128MB space for I/O is not configurable. The NORMAL zone size will be deducted based on the VM Split and some hard coded DMA zone and 128 MB space size.
I am not a guru in this space... so I might be wrong. -- 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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