[PATCH v2 2/7] mm/migrate: correct failure handling if !hugepage_migration_support()

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

We should remove the page from the list if we fail without ENOSYS,
since migrate_pages() consider error cases except -ENOMEM and -EAGAIN
as permanent failure and it assumes that the page would be removed from
the list. Without this patch, we could overcount number of failure.

In addition, we should put back the new hugepage if
!hugepage_migration_support(). If not, we would leak hugepage memory.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

diff --git a/mm/migrate.c b/mm/migrate.c
index c6ac87a..b1cfd01 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1011,7 +1011,7 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 {
 	int rc = 0;
 	int *result = NULL;
-	struct page *new_hpage = get_new_page(hpage, private, &result);
+	struct page *new_hpage;
 	struct anon_vma *anon_vma = NULL;
 
 	/*
@@ -1021,9 +1021,12 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 	 * tables or check whether the hugepage is pmd-based or not before
 	 * kicking migration.
 	 */
-	if (!hugepage_migration_support(page_hstate(hpage)))
+	if (!hugepage_migration_support(page_hstate(hpage))) {
+		putback_active_hugepage(hpage);
 		return -ENOSYS;
+	}
 
+	new_hpage = get_new_page(hpage, private, &result);
 	if (!new_hpage)
 		return -ENOMEM;
 
-- 
1.7.9.5

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