kernel/linux.git/mm/migrate_device.c, branch v7.0-rc7

mm: Fix a hmm_range_fault() livelock / starvation problem

2026-03-02T16:51:51+00:00

If hmm_range_fault() fails a folio_trylock() in do_swap_page, trying to acquire the lock of a device-private folio for migration, to ram, the function will spin until it succeeds grabbing the lock. However, if the process holding the lock is depending on a work item to be completed, which is scheduled on the same CPU as the spinning hmm_range_fault(), that work item might be starved and we end up in a livelock / starvation situation which is never resolved. This can happen, for example if the process holding the device-private folio lock is stuck in migrate_device_unmap()->lru_add_drain_all() sinc lru_add_drain_all() requires a short work-item to be run on all online cpus to complete. A prerequisite for this to happen is: a) Both zone device and system memory folios are considered in migrate_device_unmap(), so that there is a reason to call lru_add_drain_all() for a system memory folio while a folio lock is held on a zone device folio. b) The zone device folio has an initial mapcount > 1 which causes at least one migration PTE entry insertion to be deferred to try_to_migrate(), which can happen after the call to lru_add_drain_all(). c) No or voluntary only preemption. This all seems pretty unlikely to happen, but indeed is hit by the "xe_exec_system_allocator" igt test. Resolve this by waiting for the folio to be unlocked if the folio_trylock() fails in do_swap_page(). Rename migration_entry_wait_on_locked() to softleaf_entry_wait_unlock() and update its documentation to indicate the new use-case. Future code improvements might consider moving the lru_add_drain_all() call in migrate_device_unmap() to be called *after* all pages have migration entries inserted. That would eliminate also b) above. v2: - Instead of a cond_resched() in hmm_range_fault(), eliminate the problem by waiting for the folio to be unlocked in do_swap_page() (Alistair Popple, Andrew Morton) v3: - Add a stub migration_entry_wait_on_locked() for the !CONFIG_MIGRATION case. (Kernel Test Robot) v4: - Rename migrate_entry_wait_on_locked() to softleaf_entry_wait_on_locked() and update docs (Alistair Popple) v5: - Add a WARN_ON_ONCE() for the !CONFIG_MIGRATION version of softleaf_entry_wait_on_locked(). - Modify wording around function names in the commit message (Andrew Morton) Suggested-by: Alistair Popple Fixes: 1afaeb8293c9 ("mm/migrate: Trylock device page in do_swap_page") Cc: Ralph Campbell Cc: Christoph Hellwig Cc: Jason Gunthorpe Cc: Jason Gunthorpe Cc: Leon Romanovsky Cc: Andrew Morton Cc: Matthew Brost Cc: John Hubbard Cc: Alistair Popple Cc: linux-mm@kvack.org Cc: Signed-off-by: Thomas Hellström Cc: # v6.15+ Reviewed-by: John Hubbard #v3 Reviewed-by: Alistair Popple Link: https://patch.msgid.link/20260210115653.92413-1-thomas.hellstrom@linux.intel.com (cherry picked from commit a69d1ab971a624c6f112cea61536569d579c3215) Signed-off-by: Rodrigo Vivi

mm: fix minor spelling mistakes in comments

2026-01-21T03:24:48+00:00

Correct several typos in comments across files in mm/ [akpm@linux-foundation.org: also fix comment grammar, per SeongJae] Link: https://lkml.kernel.org/r/20251218150906.25042-1-klourencodev@gmail.com Signed-off-by: Kevin Lourenco Reviewed-by: SeongJae Park Acked-by: David Hildenbrand (Red Hat) Reviewed-by: Lorenzo Stoakes Signed-off-by: Andrew Morton

mm: introduce generic lazy_mmu helpers

2026-01-21T03:24:33+00:00

The implementation of the lazy MMU mode is currently entirely arch-specific; core code directly calls arch helpers: arch_{enter,leave}_lazy_mmu_mode(). We are about to introduce support for nested lazy MMU sections. As things stand we'd have to duplicate that logic in every arch implementing lazy_mmu - adding to a fair amount of logic already duplicated across lazy_mmu implementations. This patch therefore introduces a new generic layer that calls the existing arch_* helpers. Two pair of calls are introduced: * lazy_mmu_mode_enable() ... lazy_mmu_mode_disable() This is the standard case where the mode is enabled for a given block of code by surrounding it with enable() and disable() calls. * lazy_mmu_mode_pause() ... lazy_mmu_mode_resume() This is for situations where the mode is temporarily disabled by first calling pause() and then resume() (e.g. to prevent any batching from occurring in a critical section). The documentation in will be updated in a subsequent patch. No functional change should be introduced at this stage. The implementation of enable()/resume() and disable()/pause() is currently identical, but nesting support will change that. Most of the call sites have been updated using the following Coccinelle script: @@ @@ { ... - arch_enter_lazy_mmu_mode(); + lazy_mmu_mode_enable(); ... - arch_leave_lazy_mmu_mode(); + lazy_mmu_mode_disable(); ... } @@ @@ { ... - arch_leave_lazy_mmu_mode(); + lazy_mmu_mode_pause(); ... - arch_enter_lazy_mmu_mode(); + lazy_mmu_mode_resume(); ... } A couple of notes regarding x86: * Xen is currently the only case where explicit handling is required for lazy MMU when context-switching. This is purely an implementation detail and using the generic lazy_mmu_mode_* functions would cause trouble when nesting support is introduced, because the generic functions must be called from the current task. For that reason we still use arch_leave() and arch_enter() there. * x86 calls arch_flush_lazy_mmu_mode() unconditionally in a few places, but only defines it if PARAVIRT_XXL is selected, and we are removing the fallback in . Add a new fallback definition to to keep things building. Link: https://lkml.kernel.org/r/20251215150323.2218608-8-kevin.brodsky@arm.com Signed-off-by: Kevin Brodsky Acked-by: David Hildenbrand Reviewed-by: Anshuman Khandual Reviewed-by: Yeoreum Yun Cc: Alexander Gordeev Cc: Andreas Larsson Cc: Borislav Betkov Cc: Boris Ostrovsky Cc: Catalin Marinas Cc: Christophe Leroy Cc: David Hildenbrand (Red Hat) Cc: David S. Miller Cc: David Woodhouse Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Jann Horn Cc: Juegren Gross Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Madhavan Srinivasan Cc: Michael Ellerman Cc: Michal Hocko Cc: Mike Rapoport Cc: Nicholas Piggin Cc: Peter Zijlstra Cc: Ritesh Harjani (IBM) Cc: Ryan Roberts Cc: Suren Baghdasaryan Cc: Thomas Gleinxer Cc: Venkat Rao Bagalkote Cc: Vlastimil Babka Cc: Will Deacon Signed-off-by: Andrew Morton

mm/huge_memory.c: introduce folio_split_unmapped

2025-11-24T23:08:53+00:00

Unmapped was added as a parameter to __folio_split() and related call sites to support splitting of folios already in the midst of a migration. This special case arose for device private folio migration since during migration there could be a disconnect between source and destination on the folio size. Introduce folio_split_unmapped() to handle this special case. Also refactor code and add __folio_freeze_and_split_unmapped() helper that is common to both __folio_split() and folio_split_unmapped(). This in turn removes the special casing introduced by the unmapped parameter in __folio_split(). [balbirs@nvidia.com: v2] Link: https://lkml.kernel.org/r/20251115084041.3914728-1-balbirs@nvidia.com [balbirs@nvidia.com: fix clang-20 build] Link: https://lkml.kernel.org/r/20251120134232.3588203-1-balbirs@nvidia.com [akpm@linux-foundation.org: add `inline' to shmem_uncharge() stub, per Balbir] Link: https://lkml.kernel.org/r/20251114012228.2634882-1-balbirs@nvidia.com Signed-off-by: Balbir Singh Suggested-by: Zi Yan Acked-by: Zi Yan Cc: David Hildenbrand Cc: Joshua Hahn Cc: Rakie Kim Cc: Byungchul Park Cc: Gregory Price Cc: Ying Huang Cc: Alistair Popple Cc: Oscar Salvador Cc: Lorenzo Stoakes Cc: Baolin Wang Cc: "Liam R. Howlett" Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Barry Song Cc: Lyude Paul Cc: Danilo Krummrich Cc: David Airlie Cc: Simona Vetter Cc: Ralph Campbell Cc: Mika Penttilä Cc: Matthew Brost Cc: Francois Dugast Signed-off-by: Andrew Morton

mm: eliminate further swapops predicates

2025-11-24T23:08:52+00:00

Having converted so much of the code base to software leaf entries, we can mop up some remaining cases. We replace is_pfn_swap_entry(), pfn_swap_entry_to_page(), is_writable_device_private_entry(), is_device_exclusive_entry(), is_migration_entry(), is_writable_migration_entry(), is_readable_migration_entry(), swp_offset_pfn() and pfn_swap_entry_folio() with softleaf equivalents. No functional change intended. Link: https://lkml.kernel.org/r/956bc9c031604811c0070d2f4bf2f1373f230213.1762812360.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes Cc: Alexander Gordeev Cc: Alistair Popple Cc: Al Viro Cc: Arnd Bergmann Cc: Axel Rasmussen Cc: Baolin Wang Cc: Baoquan He Cc: Barry Song Cc: Byungchul Park Cc: Chengming Zhou Cc: Chris Li Cc: Christian Borntraeger Cc: Christian Brauner Cc: Claudio Imbrenda Cc: David Hildenbrand Cc: Dev Jain Cc: Gerald Schaefer Cc: Gregory Price Cc: Heiko Carstens Cc: "Huang, Ying" Cc: Hugh Dickins Cc: Jan Kara Cc: Jann Horn Cc: Janosch Frank Cc: Jason Gunthorpe Cc: Joshua Hahn Cc: Kairui Song Cc: Kemeng Shi Cc: Lance Yang Cc: Leon Romanovsky Cc: Liam Howlett Cc: Mathew Brost Cc: Matthew Wilcox (Oracle) Cc: Miaohe Lin Cc: Michal Hocko Cc: Mike Rapoport Cc: Muchun Song Cc: Naoya Horiguchi Cc: Nhat Pham Cc: Nico Pache Cc: Oscar Salvador Cc: Pasha Tatashin Cc: Peter Xu Cc: Rakie Kim Cc: Rik van Riel Cc: Ryan Roberts Cc: SeongJae Park Cc: Suren Baghdasaryan Cc: Sven Schnelle Cc: Vasily Gorbik Cc: Vlastimil Babka Cc: Wei Xu Cc: xu xin Cc: Yuanchu Xie Cc: Zi Yan Signed-off-by: Andrew Morton

mm: replace pmd_to_swp_entry() with softleaf_from_pmd()

2025-11-24T23:08:51+00:00

Introduce softleaf_from_pmd() to do the equivalent operation for PMDs that softleaf_from_pte() fulfils, and cascade changes through code base accordingly, introducing helpers as necessary. We are then able to eliminate pmd_to_swp_entry(), is_pmd_migration_entry(), is_pmd_device_private_entry() and is_pmd_non_present_folio_entry(). This further establishes the use of leaf operations throughout the code base and further establishes the foundations for eliminating is_swap_pmd(). No functional change intended. [lorenzo.stoakes@oracle.com: check writable, not readable/writable, per Vlastimil] Link: https://lkml.kernel.org/r/cd97b6ec-00f9-45a4-9ae0-8f009c212a94@lucifer.local Link: https://lkml.kernel.org/r/3fb431699639ded8fdc63d2210aa77a38c8891f1.1762812360.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes Reviewed-by: SeongJae Park \ Reviewed-by: Vlastimil Babka Cc: Alexander Gordeev Cc: Alistair Popple Cc: Al Viro Cc: Arnd Bergmann Cc: Axel Rasmussen Cc: Baolin Wang Cc: Baoquan He Cc: Barry Song Cc: Byungchul Park Cc: Chengming Zhou Cc: Chris Li Cc: Christian Borntraeger Cc: Christian Brauner Cc: Claudio Imbrenda Cc: David Hildenbrand Cc: Dev Jain Cc: Gerald Schaefer Cc: Gregory Price Cc: Heiko Carstens Cc: "Huang, Ying" Cc: Hugh Dickins Cc: Jan Kara Cc: Jann Horn Cc: Janosch Frank Cc: Jason Gunthorpe Cc: Joshua Hahn Cc: Kairui Song Cc: Kemeng Shi Cc: Lance Yang Cc: Leon Romanovsky Cc: Liam Howlett Cc: Mathew Brost Cc: Matthew Wilcox (Oracle) Cc: Miaohe Lin Cc: Michal Hocko Cc: Mike Rapoport Cc: Muchun Song Cc: Naoya Horiguchi Cc: Nhat Pham Cc: Nico Pache Cc: Oscar Salvador Cc: Pasha Tatashin Cc: Peter Xu Cc: Rakie Kim Cc: Rik van Riel Cc: Ryan Roberts Cc: Suren Baghdasaryan Cc: Sven Schnelle Cc: Vasily Gorbik Cc: Wei Xu Cc: xu xin Cc: Yuanchu Xie Cc: Zi Yan Signed-off-by: Andrew Morton

mm/migrate_device: add THP splitting during migration

2025-11-24T23:08:48+00:00

Implement migrate_vma_split_pages() to handle THP splitting during the migration process when destination cannot allocate compound pages. This addresses the common scenario where migrate_vma_setup() succeeds with MIGRATE_PFN_COMPOUND pages, but the destination device cannot allocate large pages during the migration phase. Key changes: - migrate_vma_split_pages(): Split already-isolated pages during migration - Enhanced folio_split() and __split_unmapped_folio() with isolated parameter to avoid redundant unmap/remap operations This provides a fallback mechansim to ensure migration succeeds even when large page allocation fails at the destination. [matthew.brost@intel.com: add THP splitting during migration] Link: https://lkml.kernel.org/r/20251120230825.181072-2-matthew.brost@intel.com Link: https://lkml.kernel.org/r/20251001065707.920170-12-balbirs@nvidia.com Signed-off-by: Balbir Singh Signed-off-by: Matthew Brost Cc: David Hildenbrand Cc: Zi Yan Cc: Joshua Hahn Cc: Rakie Kim Cc: Byungchul Park Cc: Gregory Price Cc: Ying Huang Cc: Alistair Popple Cc: Oscar Salvador Cc: Lorenzo Stoakes Cc: Baolin Wang Cc: "Liam R. Howlett" Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Barry Song Cc: Lyude Paul Cc: Danilo Krummrich Cc: David Airlie Cc: Simona Vetter Cc: Ralph Campbell Cc: Mika Penttilä Cc: Francois Dugast Signed-off-by: Andrew Morton

mm/migrate_device: implement THP migration of zone device pages

2025-11-24T23:08:48+00:00

MIGRATE_VMA_SELECT_COMPOUND will be used to select THP pages during migrate_vma_setup() and MIGRATE_PFN_COMPOUND will make migrating device pages as compound pages during device pfn migration. migrate_device code paths go through the collect, setup and finalize phases of migration. The entries in src and dst arrays passed to these functions still remain at a PAGE_SIZE granularity. When a compound page is passed, the first entry has the PFN along with MIGRATE_PFN_COMPOUND and other flags set (MIGRATE_PFN_MIGRATE, MIGRATE_PFN_VALID), the remaining entries (HPAGE_PMD_NR - 1) are filled with 0's. This representation allows for the compound page to be split into smaller page sizes. migrate_vma_collect_hole(), migrate_vma_collect_pmd() are now THP page aware. Two new helper functions migrate_vma_collect_huge_pmd() and migrate_vma_insert_huge_pmd_page() have been added. migrate_vma_collect_huge_pmd() can collect THP pages, but if for some reason this fails, there is fallback support to split the folio and migrate it. migrate_vma_insert_huge_pmd_page() closely follows the logic of migrate_vma_insert_page() Support for splitting pages as needed for migration will follow in later patches in this series. Link: https://lkml.kernel.org/r/20251001065707.920170-8-balbirs@nvidia.com Signed-off-by: Balbir Singh Cc: David Hildenbrand Cc: Zi Yan Cc: Joshua Hahn Cc: Rakie Kim Cc: Byungchul Park Cc: Gregory Price Cc: Ying Huang Cc: Alistair Popple Cc: Oscar Salvador Cc: Lorenzo Stoakes Cc: Baolin Wang Cc: "Liam R. Howlett" Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Barry Song Cc: Lyude Paul Cc: Danilo Krummrich Cc: David Airlie Cc: Simona Vetter Cc: Ralph Campbell Cc: Mika Penttilä Cc: Matthew Brost Cc: Francois Dugast Signed-off-by: Andrew Morton

mm/migrate_device: handle partially mapped folios during collection

2025-11-24T23:08:48+00:00

Extend migrate_vma_collect_pmd() to handle partially mapped large folios that require splitting before migration can proceed. During PTE walk in the collection phase, if a large folio is only partially mapped in the migration range, it must be split to ensure the folio is correctly migrated. [matthew.brost@intel.com: handle partially mapped folios during split] Link: https://lkml.kernel.org/r/20251120230825.181072-1-matthew.brost@intel.com Link: https://lkml.kernel.org/r/20251001065707.920170-7-balbirs@nvidia.com Signed-off-by: Balbir Singh Signed-off-by: Matthew Brost Cc: David Hildenbrand Cc: Zi Yan Cc: Joshua Hahn Cc: Rakie Kim Cc: Byungchul Park Cc: Gregory Price Cc: Ying Huang Cc: Alistair Popple Cc: Oscar Salvador Cc: Lorenzo Stoakes Cc: Baolin Wang Cc: "Liam R. Howlett" Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Barry Song Cc: Lyude Paul Cc: Danilo Krummrich Cc: David Airlie Cc: Simona Vetter Cc: Ralph Campbell Cc: Mika Penttilä Cc: Francois Dugast Signed-off-by: Andrew Morton

treewide: remove MIGRATEPAGE_SUCCESS

2025-09-13T23:54:50+00:00

At this point MIGRATEPAGE_SUCCESS is misnamed for all folio users, and now that we remove MIGRATEPAGE_UNMAP, it's really the only "success" return value that the code uses and expects. Let's just get rid of MIGRATEPAGE_SUCCESS completely and just use "0" for success. Link: https://lkml.kernel.org/r/20250811143949.1117439-3-david@redhat.com Signed-off-by: David Hildenbrand Reviewed-by: Zi Yan [mm] Acked-by: Dave Kleikamp [jfs] Acked-by: David Sterba [btrfs] Acked-by: Greg Kroah-Hartman Reviewed-by: Byungchul Park Cc: Alistair Popple Cc: Al Viro Cc: Arnd Bergmann Cc: Benjamin LaHaise Cc: Chris Mason Cc: Christian Brauner Cc: Christophe Leroy Cc: Dave Kleikamp Cc: Eugenio Pé rez Cc: Gregory Price Cc: "Huang, Ying" Cc: Jan Kara Cc: Jason Wang Cc: Jerrin Shaji George Cc: Josef Bacik Cc: Joshua Hahn Cc: Madhavan Srinivasan Cc: Mathew Brost Cc: Michael Ellerman Cc: "Michael S. Tsirkin" Cc: Minchan Kim Cc: Muchun Song Cc: Nicholas Piggin Cc: Oscar Salvador Cc: Rakie Kim Cc: Sergey Senozhatsky Cc: Xuan Zhuo Cc: Lance Yang Signed-off-by: Andrew Morton