Is this is a question that popped up to your mind arbitrarily or do you have a specific system at hand which triggered you to ponder over the design of the kernel ? I felt the answer to this question is not straight forward but is multi faceted and to be discussed in a specific context.
On Sat, May 11, 2013 at 9:02 AM, Paul Davies C <pauldaviesc@xxxxxxxxx> wrote:
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 Cvivafoss.blogspot.com
--
Regards,
Prabhunath G
Linux Trainer
Bangalore
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