Re: Query regarding adding physical memory after uvm_page_physload

[Masao Uebayashi <uebayasi%gmail.com@localhost>]

On Sun, Jun 26, 2011 at 10:13 PM, Bharat Joshi 
<bharat.josh%gmail.com@localhost> wrote:
>>>       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

I don't understand what "which needs to be added in physical memory
later".  Could you elaborate this?

> 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
>