Hi
I am reading linux kernel development (Robert love, third edition), I hit upon a line which states "kernel memory is not pageable"

My understanding is that physical memory (RAM) is divided into pages (size of 4KB etc, based on configuration).

Can someone help in with the meaning of the statement "kernel memory is not pageable" ... RAM is divided into pages right? or it means that those pages which are allocated for kernel are not swapable?

I googled (http://www.google.co.in/search?q=ker...-a&safe=active) but I couldnt get satisfactory answer.

I am a newbie in kernel and any pointers/link will help me..

thanks

Hello vrs,

I am not linux kernel developer but the following google search may be more useful to you.

also, you may want to check this http://comments.gmane.org/gmane.linu...lnewbies/41877

HTH

thanks...
in simple layman terms, it means those pages are not swappable. they *will* be in RAM for ever.

you mixed the verb paging and the noun page. The memory is divided into pages (noun), or blocks. The memory can be swapped or paged (verb).
The kernel memory is always part of the main physical memory, it cannot be swapped.

Memory is divided into pages, so when we say "The memory is paged", it means that portion of memory is "pinned" at physical (main) memory.
Please correct me if wrong...

Thanks again

see here: http://en.wikipedia.org/wiki/Paging. The paged memory is currently not available, because it is now located in the swap area (a bit similar to a book and the pages, it is "another" page, not the one what you currently reading). The kernel memory cannot be paged, it means it is pinned.

1 members found this post helpful.

Got it, thanks...

Since the kernel is the portion of the system that is responsible for the implementation of virtual-memory paging, there must always be an "always resident" portion of the kernel which can never experience page-faults itself.

If the microprocessor, in handling a page-fault interrupt, determines that the page-fault handler itself is not resident in memory, the processor itself will halt ... quicker than a tennis match ... with a so-called "double fault."

This does not mean that code within the kernel cannot experience a page-fault. In fact, that's one of the reasons for the "kernel thread" architecture, which also allows kernel-code to start I/O operations and to wait for those operations to be completed. But all of the code that is directly or indirectly responsible for handling CPU and/or hardware interrupts must at all times be permanently resident.

The kernel accomplishes this by setting up segment and page-table entries which map these areas of memory as what we old IBMers would call "virtual = real." And these pages are locked so that no part of the virtual-memory system will ever, ever consider them eligible for swap ... "no way, no how, no matter how drunk you are." Now, the processor can be put into virtual-memory mode by the so-called "trampoline," and it can (and does...) stay that way forever.