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SubjectRe: [PATCH 1/2] Export get_user_pages_fast
On Thu, 31 Jul 2008 09:43:59 +0300 Avi Kivity <avi@qumranet.com> wrote:

> > #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.

Excellent question!


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