ubifs: fix page_count in ->ubifs_migrate_page()

From: zhangjun
Date: Wed Dec 12 2018 - 09:14:30 EST

Because the PagePrivate() in UBIFS is different meanings,
alloc_cma() will fail when one dirty page cache located in
the type of MIGRATE_CMA

If not adjust the 'extra_count' for dirty page,
ubifs_migrate_page() -> migrate_page_move_mapping() will
always return -EAGAIN for:
expected_count += page_has_private(page)
This causes the migration to fail until the page cache is cleaned

In general, PagePrivate() indicates that buff_head is already bound
to this page, and at the same time page_count() will also increase.
But UBIFS set private flag when the cache is dirty, and page_count()
not increase.
Therefore, the expected_count of UBIFS is different from the general

Signed-off-by: zhangjun <openzhangj@xxxxxxxxx>
fs/ubifs/file.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index 1b78f2e..2136a5c 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -1480,8 +1480,15 @@ static int ubifs_migrate_page(struct address_space *mapping,
struct page *newpage, struct page *page, enum migrate_mode mode)
int rc;
+ int extra_count;

- rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
+ /*
+ * UBIFS is using PagePrivate() which can have different meanings across
+ * filesystems. So here adjusting the 'extra_count' make it work.
+ */
+ extra_count = 0 - page_has_private(page);
+ rc = migrate_page_move_mapping(mapping, newpage,
+ page, NULL, mode, extra_count);
return rc;