首先摘录如下URL对pagemap的描述。
https://www.kernel.org/doc/Documentation/vm/pagemap.txt
* /proc/pid/pagemap. This file lets a userspace process find out which
physical frame each virtual page is mapped to. It contains one 64-bit
value for each virtual page, containing the following data (from
fs/proc/task_mmu.c, above pagemap_read):
* Bits 0-54 page frame number (PFN) if present
* Bits 0-4 swap type if swapped
* Bits 5-54 swap offset if swapped
* Bit 55 pte is soft-dirty (see Documentation/vm/soft-dirty.txt)
* Bits 56-60 zero
* Bit 61 page is file-page or shared-anon
* Bit 62 page swapped
* Bit 63 page present
If the page is not present but in swap, then the PFN contains an
encoding of the swap file number and the page‘s offset into the
swap. Unmapped pages return a null PFN. This allows determining
precisely which pages are mapped (or in swap) and comparing mapped
pages between processes.
接下来，我们根据上述描述，给出获取虚拟地址对应的物理地址的代码
#define page_map_file "/proc/self/pagemap"
#define PFN_MASK ((((uint64_t)1)<<55)-1)
#define PFN_PRESENT_FLAG (((uint64_t)1)<<63)
int mem_addr_vir2phy(unsigned long vir, unsigned long *phy)
{
int fd;
int page_size=getpagesize();
unsigned long vir_page_idx = vir/page_size;
unsigned long pfn_item_offset = vir_page_idx*sizeof(uint64_t);
uint64_t pfn_item;
fd = open(page_map_file, O_RDONLY);
if (fd<0)
{
printf("open %s failed", page_map_file);
return -1;
}
if ((off_t)-1 == lseek(fd, pfn_item_offset, SEEK_SET))
{
printf("lseek %s failed", page_map_file);
return -1;
}
if (sizeof(uint64_t) != read(fd, &pfn_item, sizeof(uint64_t)))
{
printf("read %s failed", page_map_file);
return -1;
}
if (0==(pfn_item & PFN_PRESENT_FLAG))
{
printf("page is not present");
return -1;
}
*phy = (pfn_item & PFN_MASK)*page_size + vir % page_size;
return 0;
}
原文：http://blog.csdn.net/crazycoder8848/article/details/38958075