On Tue, Oct 11, 2016 at 05:58:15PM +0200, Jan Kara wrote:

On Thu 15-09-16 14:54:55, Kirill A. Shutemov wrote:

quoted

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 <redacted>
---
 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);

I'm not quite sure why this is needed. When you have multiorder entry in
the radix tree for your huge page, then you should not get more entries in
the pagevec for your huge page. What do I miss?

For compatibility reason find_get_entries() (which is called by
pagevec_lookup_entries()) collects all subpages of huge page in the range
(head/tails). See patch [07/41]

So huge page, which is fully in the range it will be pinned up to
PAGEVEC_SIZE times.

-- 
 Kirill A. Shutemov