memory

pfn_to_page and page_to_pfn

###summary
page_to_pfn and pfn_to_page are often used in kernel.

for PP81, kernel uses CONFIG_DISCONTIGMEM + NUMA.
Every node has node_mem_map and node_start_pfnto help the page/pfn covertion.
node_start_pfn is the first page’s pfn of this node.
node_mem_map stores all the struct page of this node.

so thete is a map between them:

`node_start_pfn + i` <===> `node_mem_map[i]`

The key is how to get node id by pfn or page.
the corresponding function is pfn_to_nid and page_to_nid

page_to_nid is simpile.
the node id is store in struct page ->flags
while pfn_to_nid(for pp81), it convert to pageaddress and then turn to pa_to_nid.

感觉这个实现有点罗嗦！
直接在include/asm-generic/memory_model.h 把pa_to_nid 定义一个 arch_pfn_to_nid宏。
省得pfn转为pa以后，又转为pfn。

pfn_to_page

funtion defination:
include/asm-generic/memory_model.h

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73 #define pfn_to_page __pfn_to_page
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33 #elif defined(CONFIG_DISCONTIGMEM)
34    
35 #define __pfn_to_page(pfn)                      \
36 ({      unsigned long __pfn = (pfn);            \
37         unsigned long __nid = arch_pfn_to_nid(__pfn);  \
38         NODE_DATA(__nid)->node_mem_map + arch_local_page_offset(__pfn, __nid);\
39 })

arch_local_page_offset

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18 #ifndef arch_local_page_offset
19 #define arch_local_page_offset(pfn, nid)        \
20         ((pfn) - NODE_DATA(nid)->node_start_pfn)
21 #endif

arch_pfn_to_nid

call trace:

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arch_pfn_to_nid 
  --> pfn_to_nid
    -->pa_to_nid((pfn) << PAGE_SHIFT)
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14 #ifndef arch_pfn_to_nid
15 #define arch_pfn_to_nid(pfn)    pfn_to_nid(pfn)
16 #endif

arch/mips/include/asm/mmzone.h

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11 #ifdef CONFIG_DISCONTIGMEM
12 
13 #define pfn_to_nid(pfn)         pa_to_nid((pfn) << PAGE_SHIFT)

arch/mips/include/asm/mach-netlogic/mmzone.h

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 52 static inline unsigned int pa_to_nid(unsigned long addr)
 53 {
 54         unsigned int  i;
 55         unsigned long pfn = addr >> PAGE_SHIFT;
 56
 57         /* TODO: Implement this using NODE_DATA */
 58         for (i = 0; i < NLM_MAX_CPU_NODE; i++) {
 59
 60                 if ((!node_online(i)) || ((NODE_MEM_DATA(i)->low_pfn == 0) && (NODE_MEM_DATA(i)->high_pfn == 0)))
 61                         continue;
 62
 63                 if (pfn >= NODE_MEM_DATA(i)->low_pfn && pfn <= NODE_MEM_DATA(i)->high_pfn)
 64                         return i;
 65         }
....

page_to_pfn

include/asm-generic/memory_model.h

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72 #define page_to_pfn __page_to_pfn
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41 #define __page_to_pfn(pg)                                               \
42 ({      struct page *__pg = (pg);                                       \
43         struct pglist_data *__pgdat = NODE_DATA(page_to_nid(__pg));     \
44         (unsigned long)(__pg - __pgdat->node_mem_map) +                 \
45          __pgdat->node_start_pfn;                                       \
46 })

page_to_nid

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538 #ifdef NODE_NOT_IN_PAGE_FLAGS
539 extern int page_to_nid(struct page *page);
540 #else
541 static inline int page_to_nid(struct page *page)
542 {
543         return (page->flags >> NODES_PGSHIFT) & NODES_MASK;
544 }
545 #endif