Subject: Re: [PATCH 10/16] mm: rename CONFIG_HAVE_GENERIC_GUP to CONFIG_HAVE_FAST_GUP

From: Jason Gunthorpe <[email-masked]>
Date: Fri, 21 Jun 2019 11:28:24 -0300

On Tue, Jun 11, 2019 at 04:40:56PM +0200, Christoph Hellwig wrote:
> We only support the generic GUP now, so rename the config option to
> be more clear, and always use the mm/Kconfig definition of the
> symbol and select it from the arch Kconfigs.

Looks OK to me

Reviewed-by: Jason Gunthorpe <[email-masked]>

But could you also roll something like this in to the series? There is
no longer any reason for the special __weak stuff that I can see -
just follow the normal pattern for stubbing config controlled
functions through the header file.

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0e8834ac32b76c..13b1cb573383d5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1561,8 +1561,17 @@ long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
 long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
 		    struct page **pages, unsigned int gup_flags);
 
+#ifdef CONFIG_HAVE_FAST_GUP
 int get_user_pages_fast(unsigned long start, int nr_pages,
 			unsigned int gup_flags, struct page **pages);
+#else
+static inline int get_user_pages_fast(unsigned long start, int nr_pages,
+				      unsigned int gup_flags,
+				      struct page **pages)
+{
+	return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);
+}
+#endif
 
 /* Container for pinned pfns / pages */
 struct frame_vector {
@@ -1668,8 +1677,17 @@ extern int mprotect_fixup(struct vm_area_struct *vma,
 /*
  * doesn't attempt to fault and will return short.
  */
+#ifdef CONFIG_HAVE_FAST_GUP
 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 			  struct page **pages);
+#else
+static inline int __get_user_pages_fast(unsigned long start, int nr_pages,
+					int write, struct page **pages)
+{
+	return 0;
+}
+#endif
+
 /*
  * per-process(per-mm_struct) statistics.
  */
diff --git a/mm/util.c b/mm/util.c
index 9834c4ab7d8e86..68575a315dc5ad 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -300,53 +300,6 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 }
 #endif
 
-/*
- * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
- * back to the regular GUP.
- * Note a difference with get_user_pages_fast: this always returns the
- * number of pages pinned, 0 if no pages were pinned.
- * If the architecture does not support this function, simply return with no
- * pages pinned.
- */
-int __weak __get_user_pages_fast(unsigned long start,
-				 int nr_pages, int write, struct page **pages)
-{
-	return 0;
-}
-EXPORT_SYMBOL_GPL(__get_user_pages_fast);
-
-/**
- * get_user_pages_fast() - pin user pages in memory
- * @start:	starting user address
- * @nr_pages:	number of pages from start to pin
- * @gup_flags:	flags modifying pin behaviour
- * @pages:	array that receives pointers to the pages pinned.
- *		Should be at least nr_pages long.
- *
- * get_user_pages_fast provides equivalent functionality to get_user_pages,
- * operating on current and current->mm, with force=0 and vma=NULL. However
- * unlike get_user_pages, it must be called without mmap_sem held.
- *
- * get_user_pages_fast may take mmap_sem and page table locks, so no
- * assumptions can be made about lack of 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 so
- * callers need to carefully consider what to use. On many architectures,
- * get_user_pages_fast simply falls back to get_user_pages.
- *
- * Return: number of pages pinned. This may be fewer than the number
- * requested. If nr_pages is 0 or negative, returns 0. If no pages
- * were pinned, returns -errno.
- */
-int __weak get_user_pages_fast(unsigned long start,
-				int nr_pages, unsigned int gup_flags,
-				struct page **pages)
-{
-	return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);
-}
-EXPORT_SYMBOL_GPL(get_user_pages_fast);
-
 unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
 	unsigned long len, unsigned long prot,
 	unsigned long flag, unsigned long pgoff)