[PATCHv1, RFC 12/33] truncate: make sure invalidate_mapping_pages() can discard huge pages

[Kirill A. Shutemov]

invalidate_inode_page() has expectation about page_count() of the page
-- if it's not 2 (one to caller, one to radix-tree), it will not be
dropped. That condition almost never met for THPs -- tail pages are
pinned to the pagevec.

Let's drop them, before calling invalidate_inode_page().

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 mm/truncate.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/truncate.c b/mm/truncate.c
index a01cce450a26..ce904e4b1708 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -504,10 +504,21 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
 				/* 'end' is in the middle of THP */
 				if (index ==  round_down(end, HPAGE_PMD_NR))
 					continue;
+				/*
+				 * invalidate_inode_page() expects
+				 * page_count(page) == 2 to drop page from page
+				 * cache -- drop tail pages references.
+				 */
+				get_page(page);
+				pagevec_release(&pvec);
 			}
 
 			ret = invalidate_inode_page(page);
 			unlock_page(page);
+
+			if (PageTransHuge(page))
+				put_page(page);
+
 			/*
 			 * Invalidation is a hint that the page is no longer
 			 * of interest and try to speed up its reclaim.
-- 
2.8.1