On Fri, Aug 17, 2012 at 12:19 AM, Ezequiel Garcia [off-list ref]wrote:

Hey Amar,

On Thu, Aug 16, 2012 at 3:39 PM, Amarnath Revanna
[off-list ref] wrote:

quoted

Just want to add a little more for better understanding:

When I spoke about .init section of the final kernel image, please note

that

quoted

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

quoted

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

quoted

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.

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