+ mm-migrate-putback-split-folios-when-numa-hint-migration-fails.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/migrate: putback split folios when numa hint migration fails
has been added to the -mm mm-unstable branch.  Its filename is
     mm-migrate-putback-split-folios-when-numa-hint-migration-fails.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate-putback-split-folios-when-numa-hint-migration-fails.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: Peter Xu <peterx@redhat.com>
Subject: mm/migrate: putback split folios when numa hint migration fails
Date: Mon, 8 Jul 2024 17:55:37 -0400

This issue is not from any report yet, but by code observation only.

This is yet another fix besides Hugh's patch [1] but on relevant code
path, where eager split of folio can happen if the folio is already on
deferred list during a folio migration.

Here the issue is NUMA path (migrate_misplaced_folio()) may start to
encounter such folio split now even with MR_NUMA_MISPLACED hint applied. 
Then when migrate_pages() didn't migrate all the folios, it's possible the
split small folios be put onto the list instead of the original folio. 
Then putting back only the head page won't be enough.

Fix it by putting back all the folios on the list.

[1] https://lore.kernel.org/all/46c948b4-4dd8-6e03-4c7b-ce4e81cfa536@google.com/

Link: https://lkml.kernel.org/r/20240708215537.2630610-1-peterx@redhat.com
Fixes: 7262f208ca68 ("mm/migrate: split source folio if it is on deferred split list")
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/migrate.c |   10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

--- a/mm/migrate.c~mm-migrate-putback-split-folios-when-numa-hint-migration-fails
+++ a/mm/migrate.c
@@ -2627,14 +2627,8 @@ int migrate_misplaced_folio(struct folio
 	nr_remaining = migrate_pages(&migratepages, alloc_misplaced_dst_folio,
 				     NULL, node, MIGRATE_ASYNC,
 				     MR_NUMA_MISPLACED, &nr_succeeded);
-	if (nr_remaining) {
-		if (!list_empty(&migratepages)) {
-			list_del(&folio->lru);
-			node_stat_mod_folio(folio, NR_ISOLATED_ANON +
-					folio_is_file_lru(folio), -nr_pages);
-			folio_putback_lru(folio);
-		}
-	}
+	if (nr_remaining && !list_empty(&migratepages))
+		putback_movable_pages(&migratepages);
 	if (nr_succeeded) {
 		count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_succeeded);
 		if (!node_is_toptier(folio_nid(folio)) && node_is_toptier(node))
_

Patches currently in -mm which might be from peterx@redhat.com are

mm-migrate-putback-split-folios-when-numa-hint-migration-fails.patch