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help with highmem

I was wondering why if CONFIG_HIGHMEM is NOT turned on, the vmalloc area

goes almost to the end of the 4GB boundary:

VMALLOC_END = FIXADDR_START - 2*PAGE_SIZE
- or -
VMALLOC_END = (FIXADDR_TOP - FIXADDR_SIZE) - 2*PAGE_SIZE
- or - (on my particular setup)
VMALLOC_END = (FFFFE000h - 4*PAGE_SIZE) - 2*PAGE_SIZE

In any case it is pretty close to the 4GB boundary

BUT when you have CONFIG_HIGHMEM turned on:

VMALLOC_END = PKMAP_BASE - 2*PAGE_SIZE

I realize you need room for the pkmap_count array but the array only
allows for 1024 pages.
If PKMAP_BASE = FE000000h then this fills the address space upto
FE400000.  What is being used in the remaining section of the address
space?

Couldn't PKMAP_BASE be moved up (allow for a larger vmalloc area) or
enlarge the pkmap_count array up to the point of VMALLOC_END as when
CONFIG_HIGHMEM is turned off?

Thanks for any help.

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