[PATCH v1 1/3] mm/gup: Export check_and_migrate_movable_pages()

[Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>]

For drivers that would like to migrate pages out of the movable
zone (or CMA) in order to pin them (longterm) for DMA, using
check_and_migrate_movable_pages() directly provides a convenient
option instead of duplicating similar checks (e.g, checking
the folios for zone, hugetlb, etc) and calling migrate_pages()
directly.

Ideally, a driver is expected to call pin_user_pages(FOLL_LONGTERM)
to migrate and pin the pages for longterm DMA but there are
situations where the GUP APIs cannot be used directly for
various reasons (e.g, when the VMA or start addr cannot be
easily determined but the relevant pages are available).

Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx>
Cc: Dongwon Kim <dongwon.kim@xxxxxxxxx>
Cc: Junxiao Chang <junxiao.chang@xxxxxxxxx>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
---
 include/linux/mm.h | 2 ++
 mm/gup.c           | 9 +++++----
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 406ab9ea818f..81871ffd3ff9 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1547,6 +1547,8 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
 void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
 				      bool make_dirty);
 void unpin_user_pages(struct page **pages, unsigned long npages);
+long check_and_migrate_movable_pages(unsigned long nr_pages,
+				     struct page **pages);
 
 static inline bool is_cow_mapping(vm_flags_t flags)
 {
diff --git a/mm/gup.c b/mm/gup.c
index 76d222ccc3ff..18beda89fcf3 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2141,8 +2141,8 @@ static int migrate_longterm_unpinnable_pages(
  * If everything is OK and all pages in the range are allowed to be pinned, then
  * this routine leaves all pages pinned and returns zero for success.
  */
-static long check_and_migrate_movable_pages(unsigned long nr_pages,
-					    struct page **pages)
+long check_and_migrate_movable_pages(unsigned long nr_pages,
+				     struct page **pages)
 {
 	unsigned long collected;
 	LIST_HEAD(movable_page_list);
@@ -2156,12 +2156,13 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
 						pages);
 }
 #else
-static long check_and_migrate_movable_pages(unsigned long nr_pages,
-					    struct page **pages)
+long check_and_migrate_movable_pages(unsigned long nr_pages,
+				     struct page **pages)
 {
 	return 0;
 }
 #endif /* CONFIG_MIGRATION */
+EXPORT_SYMBOL(check_and_migrate_movable_pages);
 
 /*
  * __gup_longterm_locked() is a wrapper for __get_user_pages_locked which
-- 
2.39.2