Re: [RFC] Tight check of pfn_valid on sparsemem

[Minchan Kim]

Hi, Kame.

On Wed, Jul 14, 2010 at 9:23 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> On Wed, 14 Jul 2010 01:44:23 +0900
> Minchan Kim <minchan.kim@xxxxxxxxx> wrote:
>
>> > If you _really_ can't make the section size smaller, and the vast
>> > majority of the sections are fully populated, you could hack something
>> > in.  We could, for instance, have a global list that's mostly readonly
>> > which tells you which sections need to be have their sizes closely
>> > inspected.  That would work OK if, for instance, you only needed to
>> > check a couple of memory sections in the system.  It'll start to suck if
>> > you made the lists very long.
>>
>> Thanks for advise. As I say, I hope Russell accept 16M section.
>>
>
> It seems what I needed was good sleep....
> How about this if 16M section is not acceptable ?
>
> == NOT TESTED AT ALL, EVEN NOT COMPILED ==
>
> register address of mem_section to memmap itself's page struct's pg->private field.
> This means the page is used for memmap of the section.
> Otherwise, the page is used for other purpose and memmap has a hole.

It's a very good idea. :)
But can this handle case that a page on memmap pages have struct page
descriptor of hole?
I mean one page can include 128 page descriptor(4096 / 32).
In there, 64 page descriptor is valid but remain 64 page descriptor is on hole.
In this case, free_memmap doesn't free the page.

I think most of system will have aligned memory of 512K(4K * 128).
But I am not sure.
-- 
Kind regards,
Minchan Kim
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