[Lguest] [PATCH 1/2] Export get_user_pages_fast
Avi Kivity
avi at qumranet.com
Thu Jul 31 16:43:59 EST 2008
Andrew Morton wrote:
> That is how it is presently implemented.
>
>
Cool.
> #ifdef CONFIG_HAVE_GET_USER_PAGES_FAST
> /*
> * get_user_pages_fast provides equivalent functionality to get_user_pages,
> * operating on current and current->mm (force=0 and doesn't return any vmas).
> *
> * get_user_pages_fast may take mmap_sem and page tables, so no assumptions
> * can be made about locking. get_user_pages_fast is to be implemented in a
> * way that is advantageous (vs get_user_pages()) when the user memory area is
> * already faulted in and present in ptes. However if the pages have to be
> * faulted in, it may turn out to be slightly slower).
> */
> int get_user_pages_fast(unsigned long start, int nr_pages, int write,
> struct page **pages);
>
> #else
> /*
> * Should probably be moved to asm-generic, and architectures can include it if
> * they don't implement their own get_user_pages_fast.
> */
> #define get_user_pages_fast(start, nr_pages, write, pages) \
> ({ \
> struct mm_struct *mm = current->mm; \
> int ret; \
> \
> down_read(&mm->mmap_sem); \
> ret = get_user_pages(current, mm, start, nr_pages, \
> write, 0, pages, NULL); \
> up_read(&mm->mmap_sem); \
> \
> ret; \
> })
> #endif
>
>
Surprised. Why not an out-of-line function? Would eliminate the
present discussion as well.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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