About SECTION_SIZE_BITS for Sparsemem

[KAMEZAWA Hiroyuki]

On Tue, 13 Jul 2010 11:05:26 +0900
Minchan Kim <minchan.kim at gmail.com> wrote:

> On Tue, Jul 13, 2010 at 9:25 AM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu at jp.fujitsu.com> wrote:

> > For example, prepare a page filled with (1 << PG_reserved).
> > and replace it with unnecessary memmap rather than freeing a page for memmap.
> 
> Hmm. I don't got your point.
> The problem is that we access struct page by pfn number not address.
> 
> You mean let's remain memmap on hole with changing PageReseved instead of free?
> 
Like a ZERO_PAGE, preparing RESERVED_PAGE, 
which is filled with (1 << PG_reserved) as

  0x00000400,0x00000400,0x00000400,0x00000400
  .....

And map this pages to every hole. Then, you only waste a page to fill all holes
because "struct page" is aligned to 4bytes.


> I think it's not a good idea to add new flag. If
> Kame. Could you review my RFC patch which makes pfn_valid check more
> tightly on sparsemem?
Sure.

Thanks,
-Kame