__get_free_pages and page_count

__get_free_pages and page_count

[Olivier Daigle]

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Hi all,
  Simple question regarding __get_free_pages and (struct page*)->count. Why 
does only the first page returned by __get_free_pages have it's count set to 
1 and all other pages have their count set to 0?

  Example:

#define ORDER 2

  unsigned long p, offset=0;
  struct page *page;
    
  if(!(p=__get_free_pages(SLAB_KERNEL, ORDER))) {
    goto err;
  }

  while(offset < PAGE_SIZE<<ORDER) {
    page=virt_to_page(p+offset);
    SC_DEBUG("  offset: %lu, page_count is %d", offset, page_count(page));
    offset+=PAGE_SIZE;
  }


Resulting output is:
Dec 18 15:36:14 meteor kernel: sc:   offset: 0, page_count is 1 
Dec 18 15:36:14 meteor kernel: sc:   offset: 4096, page_count is 0 
Dec 18 15:36:14 meteor kernel: sc:   offset: 8192, page_count is 0 
Dec 18 15:36:14 meteor kernel: sc:   offset: 12288, page_count is 0 

Thanks,

  Olivier

- -- 
Olivier Daigle <odaigle@harfangmicro.com>
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