On Fri, Aug 17, 2012 at 12:19 AM, Ezequiel Garcia <elezegarcia@gmail.com>wrote:
Hey Amar,
On Thu, Aug 16, 2012 at 3:39 PM, Amarnath Revanna <amarnath.revanna@gmail.com> wrote:
Just want to add a little more for better understanding:
When I spoke about .init section of the final kernel image, please note that this section is going to contain all the __init data (and functions) coming from _All_ the drivers and modules that were included as part of the kernel image. Hence, after initialization when we look at the print:
" [1.011596] Freeing unused kernel memory: 664k freed "
we see 664k bytes being freed.
This is a significant amount of contiguous physical memory that we can see being released by the kernel.
The same cannot be held true for a single loadable module which may be releasing just a few, virtually contiguous memory.
It's crystal clear ;-) Nice explanation. It's important to add something to clearify a bit your explanation (please correct me if I'm wrong):
When Amar is talking about "virtually contiguous" kernel memory he implies that this memory is physically *dis*contiguous, i.e. based on page-entries. This is the kind of memory used for loadable modules, for instance, modules that get loaded with modprobe.
On the other hand, built-in modules are compiled *inside* the kernel image (bzImage). The memory used for this image is physically contiguous: it's a big contiguous block of memory pages. Contiguous memory is important for kernel, and therefore is *very* important to spend some effort minimizing it.
Ezequiel, Thanks for adding the clarification here :-) Regards, -Amar
Regards, Ezequiel.