[PATCH] mm, thp: fix migration of PTE-mapped transparent huge pages

[PATCH] mm, thp: fix migration of PTE-mapped transparent huge pages

[Kirill A. Shutemov]

We don't have native support of THP migration, so we have to split huge
page into small pages in order to migrate it to different node.
This includes PTE-mapped huge pages.

I made mistake in refcounting patchset: we don't actually split
PTE-mapped huge page in queue_pages_pte_range(), if we step on head
page.

The result is that the head page is queued for migration, but none of
tail pages: putting head page on queue takes pin on the page and any
subsequent attempts of split_huge_pages() would fail and we skip queuing
tail pages.

unmap_and_move_huge_page() will eventually split the huge pages, but
only one of 512 pages would get migrated.

Let's fix the situation.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Fixes: b57a81e3e29c ("migrate_pages: try to split pages on queuing")
---
 mm/mempolicy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 8c5fd08c253c..8cbc74387df3 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -532,7 +532,7 @@ retry:
 		nid = page_to_nid(page);
 		if (node_isset(nid, *qp->nmask) == !!(flags & MPOL_MF_INVERT))
 			continue;
-		if (PageTail(page) && PageAnon(page)) {
+		if (PageTransCompound(page) && PageAnon(page)) {
 			get_page(page);
 			pte_unmap_unlock(pte, ptl);
 			lock_page(page);
-- 
2.7.0

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