The patch titled
Subject: mm: migrate: Fix return value if all subpages of THPs are migrated successfully
has been added to the -mm mm-unstable branch. Its filename is
mm-migrate-fix-return-value-if-all-subpages-of-thps-are-migrated-successfully.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate-fix-return-value-if-all-subpages-of-thps-are-migrated-successfully.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Subject: mm: migrate: Fix return value if all subpages of THPs are migrated successfully
Date: Fri, 21 Oct 2022 18:16:23 +0800
During THP migration, if THPs are not migrated but they are split and all
subpages are migrated successfully, migrate_pages() will still return the
number of THP pages that were not migrated. This will confuse the callers
of migrate_pages(). For example, the longterm pinning will failed though
all pages are migrated successfully.
Thus we should return 0 to indicate that all pages are migrated in this
case.
Link: https://lkml.kernel.org/r/fca6bb0bd48a0292a0ace2fadd0f44579a060cbb.1666335603.git.baolin.wang@xxxxxxxxxxxxxxxxx
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/migrate.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/mm/migrate.c~mm-migrate-fix-return-value-if-all-subpages-of-thps-are-migrated-successfully
+++ a/mm/migrate.c
@@ -1582,6 +1582,13 @@ out:
*/
list_splice(&ret_pages, from);
+ /*
+ * Return 0 in case all subpages of fail-to-migrate THPs are
+ * migrated successfully.
+ */
+ if (nr_thp_split && list_empty(from))
+ rc = 0;
+
count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
count_vm_events(PGMIGRATE_FAIL, nr_failed_pages);
count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded);
_
Patches currently in -mm which might be from baolin.wang@xxxxxxxxxxxxxxxxx are
mm-migrate-fix-return-value-if-all-subpages-of-thps-are-migrated-successfully.patch
mm-migrate-try-again-if-thp-split-is-failed-due-to-page-refcnt.patch
