Regarding high mem

[Rik van Riel]

On 10/17/2012 04:52 AM, Kshemendra KP wrote:

> One thing not clear to me is, during boot,  kernel is copied to 1st MB
> of the RAM in x86 architecture as this  architecture
> has ISA mem map hole (640k -to 1MB). From 1st BM till 896MB is occupied
> by the kernel. Then user space will be
> made available beyond 896 MB.  With this reasoning, it is not clear to
> me, whether user space which is present
> beyond 896 MB is in high memory.

You appear to be confusing virtual and physical memory.

Physical addresses 0 through 896MB are mapped at
virtual addresses 3GB through 3GB+896MB.

The 128MB above that are used for vmalloc, and a
few other miscellaneous things.  This 1GB of
kernel virtual memory is the same in every process.

Virtual addresses 0-3GB are used for userspace,
which each process getting its own private 3GB
sized virtual memory area.

Ranges of process virtual memory can be used,
or unused. The used ranges could be backed by
any physical memory in the system (highmem, normal &
dma zones), or not by any memory at all (backed by
swap, or on-disk file pages).

Does that make sense?