Linux MM : virtual memory address space

[pramod gurav]

On Mon, Mar 3, 2014 at 11:52 PM, priyaranjan <priyaranjan45678 at gmail.com>wrote:

> I was going through http://linux-mm.org/HighMemory
>
> "Currently the 32 bit x86 architecture is the most popular type of
> computer. In this architecture, traditionally the Linux kernel has split
> the 4GB of virtual memory address space into 3GB for user programs and 1GB
> for the kernel"
>
> What about 64-bit system? Where does the code lie in linux kernel for the
> check?
> Is there any latest and updated memory management documentation for Linux
> kernel?
>
> Regards,
> Priyaranjan
>
>
Priyaranjan,

As below link suggests:
http://users.nccs.gov/~fwang2/linux/lk_addressing.txt

Also read this blog written in chinese:

http://adam8157.info/blog/2012/07/linux-x86-64-vm/

on 64 bit arch the virtual address space is huge (2 to thr power of 64). So
the overhead of translating the virtual addresses will be high. TO avoid
this only lower 48 bits are used to form virtual addresses. This virtual
space will still be very large (256 TB) and hence the user/kernel split is
1:1 (128TB:128TB). And as suggested in link it is very unlikely that you
will have such a huge RAM(more than 128TB) installed on any machine there
is no concept of HIGHMEM.

Hope this clears the air a bit.

>
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-- 
Thanks and Regards
Pramod
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