[PATCH 1/2] mm: gup: Re-pin pages in case of trying several times to migrate

[Baolin Wang <baolin.wang@linux.alibaba.com>]

The migrate_pages() will return the number of {normal page, THP, hugetlb}
that were not migrated, or an error code. That means it can still return
the number of failure count, though the pages have been migrated
successfully with several times re-try.

So we should not use the return value of migrate_pages() to determin
if there are pages are failed to migrate. Instead we can validate the
'movable_page_list' to see if there are pages remained in the list,
which are failed to migrate. That can mitigate the failure of longterm
pinning.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 mm/gup.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 5182aba..bd8cfcd 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1914,9 +1914,10 @@ static int migrate_longterm_unpinnable_pages(
 			.gfp_mask = GFP_USER | __GFP_NOWARN,
 		};
 
-		if (migrate_pages(movable_page_list, alloc_migration_target,
-				  NULL, (unsigned long)&mtc, MIGRATE_SYNC,
-				  MR_LONGTERM_PIN, NULL)) {
+		ret = migrate_pages(movable_page_list, alloc_migration_target,
+				    NULL, (unsigned long)&mtc, MIGRATE_SYNC,
+				    MR_LONGTERM_PIN, NULL);
+		if (ret < 0 || !list_empty(movable_page_list)) {
 			ret = -ENOMEM;
 			goto err;
 		}
-- 
1.8.3.1