Kernel Memory

[Vijay Chauhan]

Thanks everyone. I think i got enough information for further study.

Thanks,
Vijay

On Thu, Jun 21, 2012 at 7:10 PM, kishore sheik ahamed
<linuxinme at gmail.com> wrote:
> Hey Vijay
>
> I am a newbie too. Just sharing what I could go through.
>
> It is said that Kernel or atleast a part of kernel needs to be non paged for
> fast interrupt access etc as pinned memory
> Wiki says
>
> Pinned/Locked/Fixed pages
>
> Operating systems have memory areas that are pinned (never swapped to
> secondary storage). For example, interrupt mechanisms rely on an array of
> pointers to their handlers, such as I/O completion and page fault. If the
> pages containing these pointers or the code that they invoke were pageable,
> interrupt-handling would become far more complex and time-consuming,
> particularly in the case of page fault interrupts. Hence, some part of the
> page table structures is not pageable.
>
> Some pages may be pinned for short periods of time, others may be pinned for
> long periods of time, and still others may need to be permanently pinned.
> For example:
>
> The paging supervisor code and drivers for secondary storage devices on
> which pages reside must be permanently pinned, as otherwise paging wouldn't
> even work because the necessary code wouldn't be available.
> Timing-dependent components may be pinned to avoid variable paging delays.
> Data buffers that are accessed directly by peripheral devices that use
> direct memory access or I/O channels must reside in pinned pages while the
> I/O operation is in progress because such devices and the buses to which
> they are attached expect to find data buffers located at physical memory
> addresses; regardless of whether the bus has a memory management unit for
> I/O, transfers cannot be stopped if a page fault occurs and then restarted
> when the page fault has been processed.
>
> There are other two discussion thread which say kernel is non-pageable and
> now due to growing kernel Data structures it is allowed
>
> http://kerneltrap.org/node/6404
>
> http://kerneltrap.org/node/8206
>
>
> Regards
>
> Kishore
>
>
>
> On Thu, Jun 21, 2012 at 5:57 PM, Vijay Chauhan <kernel.vijay at gmail.com>
> wrote:
>>
>> Hello,
>>
>> I am newbie.
>> It has been said "kernel memory is not pageable"
>> What does it mean? There is no concept of kernel virtual address?
>>
>> Any simple explanation will help me to udnerstand.
>>
>> Thanks,
>> Vijay
>>
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>
>