Basic HighMeM Question

Paraneetharan Chandrasekaran paraneetharanc at
Wed Jun 29 03:34:34 EDT 2011

On 29 June 2011 12:08, Mulyadi Santosa <mulyadi.santosa at> wrote:

> Hi :)
> On Wed, Jun 29, 2011 at 13:30, piyush moghe <pmkernel at> wrote:
> > Thanks Mulyadi and Prabhu for your enlightening description.
> You welcome :)
> > What a plight!!! memory has become soo cheap nowadays that I don't have
> less
> > than 1GB system and difficult to find someone in my knowledge having less
> > than 1 GB memory.
> In embedded world, it's still common scenario.... so it depends on
> which side we see it :) That's the flexibility Linux kernel tries to
> does well on big memory machine...but it can also run in
> small amount of memory... of course, with the right user space
> applications :) (hint: Linux slitaz, puppy, tiny core...)
> > Although does this means that pages in FCOM will never have page fault?
> Everything mapped in kernel space ( I stress the word "mapped") is
> designed to stay all the time in RAM in Linux kernel context. So based
> on that AFAIK, we won't get page fault in kernel space. This is
> strictly design choice IMHO.
> >and
> > if this is true is this the reason why we assign NULL to memory
> descriptor (
> > mm_struct ) for kernel threads?
> because kernel threads don't need to have specific address space owned
> to them. They can simply "borrow" last scheduled process' address
> space. After all, they just operate in kernel space, which is the same
> for all processes, be it kernel threads or normal task.

Thanks Mulyadi for your clarifications!
I am not getting the idea of "borrowing" last run process's address space. A
kernel thread refers only the addresses in kernel's address space (low-mem
area) which is mapped already, isnt it? How does the address space of last
run task comes into picture?

> --
> regards,
> Mulyadi Santosa
> Freelance Linux trainer and consultant
> blog:
> training:
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Paraneetharan C
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