[PATCHv4 17/25] vmscan: split file huge pages before paging them out

[Kirill A. Shutemov]

This is preparation of vmscan for file huge pages. We cannot write out
huge pages, so we need to split them on the way out.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 mm/vmscan.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index c72032dbe8db..9fa9e15594e9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -473,12 +473,14 @@ void drop_slab(void)
 
 static inline int is_page_cache_freeable(struct page *page)
 {
+	int radix_tree_pins = PageTransHuge(page) ? HPAGE_PMD_NR : 1;
+
 	/*
 	 * A freeable page cache page is referenced only by the caller
 	 * that isolated the page, the page cache radix tree and
 	 * optional buffer heads at page->private.
 	 */
-	return page_count(page) - page_has_private(page) == 2;
+	return page_count(page) - page_has_private(page) == 1 + radix_tree_pins;
 }
 
 static int may_write_to_inode(struct inode *inode, struct scan_control *sc)
@@ -548,8 +550,6 @@ static pageout_t pageout(struct page *page, struct address_space *mapping,
 	 * swap_backing_dev_info is bust: it doesn't reflect the
 	 * congestion state of the swapdevs.  Easy to fix, if needed.
 	 */
-	if (!is_page_cache_freeable(page))
-		return PAGE_KEEP;
 	if (!mapping) {
 		/*
 		 * Some data journaling orphaned pages can have
@@ -1112,6 +1112,15 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			 * starts and then write it out here.
 			 */
 			try_to_unmap_flush_dirty();
+
+			if (!is_page_cache_freeable(page))
+				goto keep_locked;
+
+			if (unlikely(PageTransHuge(page))) {
+				if (split_huge_page_to_list(page, page_list))
+					goto keep_locked;
+			}
+
 			switch (pageout(page, mapping, sc)) {
 			case PAGE_KEEP:
 				goto keep_locked;
-- 
2.7.0