Memory Management API: get_user_pages_fast,

Memory Management API: get_user_pages_fast,

Memory Management API: get_user_pages_fast

Int get_user_pages_fast (unsigned long start, int nr_pages, int write, struct page ** pages) and get_user_pages have the same effect. source code analysis: int get_user_pages_fast (unsigned long start, int nr_pages, int write, struct page ** pages) {unsigned long addr, len, end; int nr = 0, ret = 0; # the actual address needs to be mapped. The page size must be aligned with start & = PAGE_MASK; addr = start; # The length of the map len = (unsigned long) nr_pages <PAGE_SHIFT; end = start + len; # If this address cannot be read/written, If (unlikely (! Access_ OK (write? VERIFY_WRITE: VERIFY_READ, (void _ user *) start, len) return 0; if (gup_fast_permitted (start, nr_pages, write) {local_irq_disable (); gup_pgd_range (addr, end, write, pages, & nr); local_irq_enable (); ret = nr;} if (nr <nr_pages) {/* Try to get the remaining pages with get_user_pages */start + = nr <PAGE_SHIFT; pages + = nr; # get_user_pages_unlocked->__ rows->__ get_user_pages_locked to map, Before _ get_user_pages_locked is mapped to this function # ret = get_user_pages_unlocked (start, nr_pages-nr, pages, write? FOLL_WRITE: 0);/* Have to be a bit careful with return values */if (nr> 0) {if (ret <0) ret = nr; elseret + = nr;} return ret ;}