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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Apr 2025 10:02:55.6599 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d27bc3a0-bdb4-4a60-dc4e-08dd87ce2dce X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF00002320.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR12MB5936 This patch addresses a warning that occurs during memory compaction due to JFS's missing migrate_folio operation. The warning was introduced by commit 7ee3647243e5 ("migrate: Remove call to ->writepage") which added explicit warnings when filesystem don't implement migrate_folio. The syzbot reported following [1]: jfs_metapage_aops does not implement migrate_folio WARNING: CPU: 1 PID: 5861 at mm/migrate.c:955 fallback_migrate_folio mm/migrate.c:953 [inline] WARNING: CPU: 1 PID: 5861 at mm/migrate.c:955 move_to_new_folio+0x70e/0x840 mm/migrate.c:1007 Modules linked in: CPU: 1 UID: 0 PID: 5861 Comm: syz-executor280 Not tainted 6.15.0-rc1-next-20250411-syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025 RIP: 0010:fallback_migrate_folio mm/migrate.c:953 [inline] RIP: 0010:move_to_new_folio+0x70e/0x840 mm/migrate.c:1007 To fix this issue, this series implement metapage_migrate_folio() for JFS which handles both single and multiple metapages per page configurations. While most filesystems leverage existing migration implementations like filemap_migrate_folio(), buffer_migrate_folio_norefs() or buffer_migrate_folio() (which internally used folio_expected_refs()), JFS's metapage architecture requires special handling of its private data during migration. To support this, this series introduce the folio_expected_ref_count(), which calculates external references to a folio from page/swap cache, private data, and page table mappings. This standardized implementation replaces the previous ad-hoc folio_expected_refs() function and enables JFS to accurately determine whether a folio has unexpected references before attempting migration. [1]: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299 Changelogs: V5 (current): - Add folio_expected_ref_count() for refcount calculation - Add details about need of folio_expected_ref_count() for JFS V4: - https://lore.kernel.org/all/20250422114000.15003-1-shivankg@amd.com - Make folio_expected_refs() inline and rename to folio_migration_expected_refs() V3: - https://lore.kernel.org/all/20250417060630.197278-1-shivankg@amd.com - Fix typos V1/V2: - https://lore.kernel.org/all/20250413172356.561544-1-shivankg@amd.com - Implement metapage_migrate_folio() similar to buffer_migrate_folio() but specialized to move JFS metapage data #syz test: https://github.com/shivankgarg98/linux.git 69a58d5260 Shivank Garg (2): mm: Add folio_expected_ref_count() for reference count calculation jfs: implement migrate_folio for jfs_metapage_aops fs/jfs/jfs_metapage.c | 94 +++++++++++++++++++++++++++++++++++++++++++ include/linux/mm.h | 55 +++++++++++++++++++++++++ mm/migrate.c | 22 ++-------- 3 files changed, 153 insertions(+), 18 deletions(-) -- 2.34.1