+ mm-migrate-fix-return-value-if-all-subpages-of-thps-are-migrated-successfully.patch added to mm-hotfixes-unstable branch

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The patch titled
     Subject: mm: migrate: fix return value if all subpages of THPs are migrated successfully
has been added to the -mm mm-hotfixes-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-hotfixes-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: Mon, 24 Oct 2022 16:34:21 +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/de386aa864be9158d2f3b344091419ea7c38b2f7.1666599848.git.baolin.wang@xxxxxxxxxxxxxxxxx
Fixes: b5bade978e9b ("mm: migrate: fix the return value of migrate_pages()")
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Reviewed-by: Alistair Popple <apopple@xxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
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 (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




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