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[PATCHv3 21/29] vmscan: split file huge pages before paging them out

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  [PATCHv3 21/29] vmscan: split file huge pages before paging them out "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:00 +0100

#1349362 — [PATCHv3 21/29] vmscan: split file huge pages before paging them out

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@linux.intel.com>
---
 mm/vmscan.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 39e90e24caff..832a00523ffb 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

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