Mapping of ZONE_HIGHMEM in kernel address space in 32bit x86

[Paul Davies C]

In a system with 3:1 split, the ZONE_NORMAL with a size of 896MB is
permanently mapped to the kernel address space.This leaves a 128MB free
space in the Kernel address space and according to my understanding, the
ZONE_HIGHMEM pages are mapped temporarily to this 128MB part. If the system
actually had a 4GB physical memory you will be mapping(not smultaneously)
the HIHGMEM part- which is roughly 3.2GB - to this 128MB part. If that was
the case Kernel would have to frequently access HIHGMEM which implicates a
frequent change in temporaty mapping and that in my view is a penalty. So
what was the reason why ZONE_NORMAL fixed at 896MB and not something really
lower?

-- 
*Regards,*
*Paul Davies C*
vivafoss.blogspot.com
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