diff options
| author | Dev Jain <dev.jain@arm.com> | 2025-07-04 09:34:17 +0530 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-07-13 16:38:33 -0700 |
| commit | 7f810385fde490a831fdba36978a52a927b23922 (patch) | |
| tree | db09408331d6f25ceaa468b74baa009657d0b490 /mm/khugepaged.c | |
| parent | ee58e38489772f356c1ac79e0724183497e43249 (diff) | |
khugepaged: reduce race probability between migration and khugepaged
Suppose a folio is under migration, and khugepaged is also trying to
collapse it. collapse_pte_mapped_thp() will retrieve the folio from the
page cache via filemap_lock_folio(), thus taking a reference on the folio
and sleeping on the folio lock, since the lock is held by the migration
path. Migration will then fail in __folio_migrate_mapping ->
folio_ref_freeze. Reduce the probability of such a race happening
(leading to migration failure) by bailing out if we detect a PMD is marked
with a migration entry.
This fixes the migration-shared-anon-thp testcase failure on Apple M3.
Note that, this is not a "fix" since it only reduces the chance of
interference of khugepaged with migration, wherein both the kernel
functionalities are deemed "best-effort".
Link: https://lkml.kernel.org/r/20250704040417.63826-1-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/khugepaged.c')
| -rw-r--r-- | mm/khugepaged.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 1aa7ca67c756..a55fb1dcd224 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -941,6 +941,14 @@ static inline int check_pmd_state(pmd_t *pmd) if (pmd_none(pmde)) return SCAN_PMD_NONE; + + /* + * The folio may be under migration when khugepaged is trying to + * collapse it. Migration success or failure will eventually end + * up with a present PMD mapping a folio again. + */ + if (is_pmd_migration_entry(pmde)) + return SCAN_PMD_MAPPED; if (!pmd_present(pmde)) return SCAN_PMD_NULL; if (pmd_trans_huge(pmde)) |