Re: Query regarding adding physical memory after uvm_page_physload

[Bharat Joshi <bharat.josh%gmail.com@localhost>]

>>       I am currently uing NetBSD 2.0 (plan to move to new one in some
>> time). I need to add more physical memory after it has already been
>> initialized once using uvm_page_physload.
>>
>>       When I tried to call uvm_page_physload again with this new RAM
>> area, it paniced. I then found out that a flag 'VM_PHYSSEG_NOADD' in
>> vmparam.h for mips needs to be disabled. I removed this flag and then
>> things seems to have worked as expected.
>>
>>       I want expert's opinion on whether this method of adding new
>> physical memory in UVM is the right (may be the only) way in NetBSD
>> 2.0. Please do let me know.
>
> That would work to some extent.  Limitations:
>
> - Data structures are not protected with locks.
>
> - Metadata (vm_page array) is allocated in somewhere by malloc(), not
> in the newly added physseg.
>
> So, if it works for you on NetBSD 2.0, I'd say it's OK for you. ;)
>

Thanks for your response. It worked for me as all my applications are
working fine. I have not stressed this yet so we will know more about
it in coming days.

Let me tell my exact requirement. I have some memory after kernel that
is being used for some purpose. I want to free it back to physical
memory once that purpose has completed. So I disabled that flag and
allow uvm_page_physload to be called again.

I was not sure so asked this on the list. Now I have another question.
"Is there any other better way of doing this?"

Can we do something like as follows:

1. Pass avail_start in uvm_page_physload with an offset (start -
avail_start ) of the memory which needs to be added in physical memory
later. This will make sure that we have pages created for the whole
memory but only the ones available after avail_start is added as free
pages.
2. Later find the pages for this memory (start to avail_start) and
call vm_page_free for each pages.

I was thinking that such an API be available in uvm-page layer but
could not find one so not sure if something like the above can/should
be done.

So it would be great if someone can tell me ways in which this can be
achieved in a better way.

Regards,
Bharat