内核提供了一个底层的机制来获得内存，
很多函数都被定已在<linux/gfp.h>中
比如300行到304行
程序代码：300static inline struct page *
301alloc_pages(gfp_t gfp_mask, unsigned int order)
302{
303 return alloc_pages_current(gfp_mask, order);
304}
301alloc_pages(gfp_t gfp_mask, unsigned int order)
302{
303 return alloc_pages_current(gfp_mask, order);
304}
这个函数分配2^order个连续physical pages，返回值当然是指向第一个page的指针
如果想把page转换成它的虚拟地址的话用函数用下面的函数，定义在<mm/highmem.c>中
程序代码：325/**
326 * page_address - get the mapped virtual address of a page
327 * @page: &struct page to get the virtual address of
328 *
329 * Returns the page's virtual address.
330 */
331void *page_address(struct page *page)
332{
333 unsigned long flags;
334 void *ret;
335 struct page_address_slot *pas;
336
337 if (!PageHighMem(page))
338 return lowmem_page_address(page);
339
340 pas = page_slot(page);
341 ret = NULL;
342 spin_lock_irqsave(&pas->lock, flags);
343 if (!list_empty(&pas->lh)) {
344 struct page_address_map *pam;
345
346 list_for_each_entry(pam, &pas->lh, list) {
347 if (pam->page == page) {
348 ret = pam->virtual;
349 goto done;
350 }
351 }
352 }
353done:
354 spin_unlock_irqrestore(&pas->lock, flags);
355 return ret;
356}
326 * page_address - get the mapped virtual address of a page
327 * @page: &struct page to get the virtual address of
328 *
329 * Returns the page's virtual address.
330 */
331void *page_address(struct page *page)
332{
333 unsigned long flags;
334 void *ret;
335 struct page_address_slot *pas;
336
337 if (!PageHighMem(page))
338 return lowmem_page_address(page);
339
340 pas = page_slot(page);
341 ret = NULL;
342 spin_lock_irqsave(&pas->lock, flags);
343 if (!list_empty(&pas->lh)) {
344 struct page_address_map *pam;
345
346 list_for_each_entry(pam, &pas->lh, list) {
347 if (pam->page == page) {
348 ret = pam->virtual;
349 goto done;
350 }
351 }
352 }
353done:
354 spin_unlock_irqrestore(&pas->lock, flags);
355 return ret;
356}
它返回一个指向logical address的指针
如果你不需要一个实际的 struct page，
(if you have no need for the actual struct page，这句话到底是怎么一回事，不明白)
则可以用下面的函数__get_free_pages()
在mm/page_alloc.c文件中
程序代码：1969/*
1970 * Common helper functions.
1971 */
1972unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order)
1973{
1974 struct page *page;
1975
1976 /*
1977 * __get_free_pages() returns a 32-bit address, which cannot represent
1978 * a highmem page
1979 */
1980 VM_BUG_ON((gfp_mask & __GFP_HIGHMEM) != 0);
1981
1982 page = alloc_pages(gfp_mask, order);
1983 if (!page)
1984 return 0;
1985 return (unsigned long) page_address(page);
1986}
1970 * Common helper functions.
1971 */
1972unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order)
1973{
1974 struct page *page;
1975
1976 /*
1977 * __get_free_pages() returns a 32-bit address, which cannot represent
1978 * a highmem page
1979 */
1980 VM_BUG_ON((gfp_mask & __GFP_HIGHMEM) != 0);
1981
1982 page = alloc_pages(gfp_mask, order);
1983 if (!page)
1984 return 0;
1985 return (unsigned long) page_address(page);
1986}
如果只需要一个页的话
则是struct page * alloc_page(gfp_t gfp_mask)
unsigned long __get_free_page(gfp_t gfp_mask)
[ 本帖最后由 madfrogme 于 2012-8-1 02:45 编辑 ]