kernel/linux.git/include/linux/huge_mm.h, branch v7.2-rc1

mm/truncate: use folio_split() in truncate_inode_partial_folio()

2026-06-21T18:37:16+00:00

After READ_ONLY_THP_FOR_FS is removed, FS either supports large folio or not. folio_split() can be used on a FS with large folio support without worrying about getting a THP on a FS without large folio support. When READ_ONLY_THP_FOR_FS was present, a PMD large pagecache folio can appear in a FS without large folio support after khugepaged or madvise(MADV_COLLAPSE) creates it. During truncate_inode_partial_folio(), such a PMD large pagecache folio is split and if the FS does not support large folio, it needs to be split to order-0 ones and could not be split non uniformly to ones with various orders. try_folio_split_to_order() was added to handle this situation by checking folio_check_splittable(..., SPLIT_TYPE_NON_UNIFORM) to detect if the large folio is created due to READ_ONLY_THP_FOR_FS and the FS does not support large folio. Now READ_ONLY_THP_FOR_FS is removed, all large pagecache folios are created with FSes supporting large folio, this function is no longer needed and all large pagecache folios can be split non uniformly. Link: https://lore.kernel.org/20260517135416.1434539-10-ziy@nvidia.com Signed-off-by: Zi Yan Reviewed-by: Lance Yang Acked-by: David Hildenbrand (Arm) Cc: Al Viro Cc: Baolin Wang Cc: Barry Song Cc: Chris Mason Cc: Christian Brauner Cc: David Sterba Cc: Dev Jain Cc: Jan Kara Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Mike Rapoport Cc: Nico Pache Cc: Ryan Roberts Cc: Shuah Khan Cc: Song Liu Cc: Suren Baghdasaryan Cc: Vlastimil Babka Signed-off-by: Andrew Morton

mm/khugepaged: add per-order mTHP collapse failure statistics

2026-06-21T18:31:31+00:00

Add three new mTHP statistics to track collapse failures for different orders when encountering swap PTEs, excessive none PTEs, and shared PTEs: - collapse_exceed_swap_pte: Increment when mTHP collapse fails due to encountering a swap PTE. - collapse_exceed_none_pte: Counts when mTHP collapse fails due to exceeding the none PTE threshold for the given order - collapse_exceed_shared_pte: Counts when mTHP collapse fails due to encountering a shared PTE. These statistics complement the existing THP_SCAN_EXCEED_* events by providing per-order granularity for mTHP collapse attempts. The stats are exposed via sysfs under `/sys/kernel/mm/transparent_hugepage/hugepages-*/stats/` for each supported hugepage size. As we currently do not support collapsing mTHPs that contain a swap or shared entry, those statistics keep track of how often we are encountering failed mTHP collapses due to these restrictions. We will add support for mTHP collapse for anonymous pages next; lets also track when this happens at the PMD level within the per-mTHP stats. Link: https://lore.kernel.org/20260605161422.213817-9-npache@redhat.com Signed-off-by: Nico Pache Reviewed-by: Lorenzo Stoakes Acked-by: David Hildenbrand (Arm) Reviewed-by: Lance Yang Cc: Alistair Popple Cc: Andrea Arcangeli Cc: Anshuman Khandual Cc: Bagas Sanjaya Cc: Baolin Wang Cc: Barry Song Cc: Brendan Jackman Cc: Byungchul Park Cc: Catalin Marinas Cc: David Rientjes Cc: Dev Jain Cc: Gregory Price Cc: "Huang, Ying" Cc: Hugh Dickins Cc: Jan Kara Cc: Jann Horn Cc: Johannes Weiner Cc: Jonathan Corbet Cc: Joshua Hahn Cc: Kefeng Wang Cc: Liam R. Howlett Cc: "Masami Hiramatsu (Google)" Cc: Mathieu Desnoyers Cc: Matthew Brost Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Mike Rapoport Cc: Nanyong Sun Cc: Pedro Falcato Cc: Peter Xu Cc: Rafael Aquini Cc: Rakie Kim Cc: Randy Dunlap Cc: Ryan Roberts Cc: Shivank Garg Cc: Steven Rostedt Cc: Suren Baghdasaryan Cc: Takashi Iwai (SUSE) Cc: Thomas Hellström Cc: Usama Arif Cc: Usama Arif Cc: Vishal Moola (Oracle) Cc: Vlastimil Babka Cc: Wei Yang Cc: Will Deacon Cc: Yang Shi Cc: Zach O'Keefe Cc: Zi Yan Signed-off-by: Andrew Morton

mm/khugepaged: generalize alloc_charge_folio()

2026-06-21T18:31:29+00:00

Pass order to alloc_charge_folio() and update mTHP statistics. Link: https://lore.kernel.org/20260605161422.213817-3-npache@redhat.com Signed-off-by: Dev Jain Co-developed-by: Nico Pache Signed-off-by: Nico Pache Reviewed-by: Wei Yang Reviewed-by: Lance Yang Reviewed-by: Baolin Wang Reviewed-by: Lorenzo Stoakes Reviewed-by: Zi Yan Acked-by: Usama Arif Acked-by: David Hildenbrand (Arm) Cc: Alistair Popple Cc: Andrea Arcangeli Cc: Anshuman Khandual Cc: Bagas Sanjaya Cc: Barry Song Cc: Brendan Jackman Cc: Byungchul Park Cc: Catalin Marinas Cc: David Rientjes Cc: Gregory Price Cc: "Huang, Ying" Cc: Hugh Dickins Cc: Jan Kara Cc: Jann Horn Cc: Johannes Weiner Cc: Jonathan Corbet Cc: Joshua Hahn Cc: Kefeng Wang Cc: Liam R. Howlett Cc: "Masami Hiramatsu (Google)" Cc: Mathieu Desnoyers Cc: Matthew Brost Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Mike Rapoport Cc: Nanyong Sun Cc: Pedro Falcato Cc: Peter Xu Cc: Rafael Aquini Cc: Rakie Kim Cc: Randy Dunlap Cc: Ryan Roberts Cc: Shivank Garg Cc: Steven Rostedt Cc: Suren Baghdasaryan Cc: Takashi Iwai (SUSE) Cc: Thomas Hellström Cc: Usama Arif Cc: Vishal Moola (Oracle) Cc: Vlastimil Babka Cc: Will Deacon Cc: Yang Shi Cc: Zach O'Keefe Signed-off-by: Andrew Morton

mm: switch deferred split shrinker to list_lru

2026-06-09T01:21:25+00:00

The deferred split queue handles cgroups in a suboptimal fashion. The queue is per-NUMA node or per-cgroup, not the intersection. That means on a cgrouped system, a node-restricted allocation entering reclaim can end up splitting large pages on other nodes: alloc/unmap deferred_split_folio() list_add_tail(memcg->split_queue) set_shrinker_bit(memcg, node, deferred_shrinker_id) for_each_zone_zonelist_nodemask(restricted_nodes) mem_cgroup_iter() shrink_slab(node, memcg) shrink_slab_memcg(node, memcg) if test_shrinker_bit(memcg, node, deferred_shrinker_id) deferred_split_scan() walks memcg->split_queue The shrinker bit adds an imperfect guard rail. As soon as the cgroup has a single large page on the node of interest, all large pages owned by that memcg, including those on other nodes, will be split. list_lru properly sets up per-node, per-cgroup lists. As a bonus, it streamlines a lot of the list operations and reclaim walks. It's used widely by other major shrinkers already. Convert the deferred split queue as well. The list_lru per-memcg heads are instantiated on demand when the first object of interest is allocated for a cgroup, by calling folio_memcg_alloc_deferred(). Add calls to where splittable pages are created: anon faults, swapin faults, khugepaged collapse. These calls create all possible node heads for the cgroup at once, so the migration code (between nodes) doesn't need any special care. [akpm@linux-foundation.org: fix build with CONFIG_TRANSPARENT_HUGEPAGE=n] Link: https://lore.kernel.org/202605281620.lc3rtkBm-lkp@intel.com [hannes@cmpxchg.org: fix cgroup.memory=nokmem handling] Link: https://lore.kernel.org/ah9PGv12mqai84ES@cmpxchg.org Link: https://lore.kernel.org/20260527204757.2544958-10-hannes@cmpxchg.org Signed-off-by: Johannes Weiner Reported-by: Mikhail Zaslonko Tested-by: Mikhail Zaslonko Acked-by: Shakeel Butt Reviewed-by: Lorenzo Stoakes (Oracle) Acked-by: Usama Arif Reviewed-by: Kairui Song Cc: Baolin Wang Cc: Barry Song Cc: Dave Chinner Cc: David Hildenbrand (Arm) Cc: Dev Jain Cc: Lance Yang Cc: Liam R. Howlett Cc: Michal Hocko Cc: Muchun Song Cc: Nico Pache Cc: Roman Gushchin Cc: Ryan Roberts Cc: Vasily Gorbik Cc: Vlastimil Babka Cc: Zi Yan Cc: kernel test robot Signed-off-by: Andrew Morton

mm/huge_memory: move THP gfp limit helper into header

2026-06-02T22:22:21+00:00

Shmem has some special requirements for THP GFP and has to limit it in certain zones or provide a more lenient fallback. We'll use this helper for generic swap THP allocation, which needs to support shmem. For a typical GFP_HIGHUSER_MOVABLE swap-in, this helper is basically a no-op. But it's necessary for certain shmem users, mostly drivers. No feature change. Link: https://lore.kernel.org/20260517-swap-table-p4-v5-3-88ae43e064c7@tencent.com Signed-off-by: Kairui Song Acked-by: Chris Li Reviewed-by: Zi Yan Cc: Baolin Wang Cc: Baoquan He Cc: Barry Song Cc: Chengming Zhou Cc: David Hildenbrand Cc: Hugh Dickins Cc: Johannes Weiner Cc: Kemeng Shi Cc: Lorenzo Stoakes Cc: Muchun Song Cc: Nhat Pham Cc: Roman Gushchin Cc: Shakeel Butt Cc: Youngjun Park Signed-off-by: Andrew Morton

mm/huge_memory: have zap_huge_pmd return a boolean, add kdoc

2026-04-05T20:53:45+00:00

There's no need to use the ancient approach of returning an integer here, just return a boolean. Also update flush_needed to be a boolean, similarly. Also add a kdoc comment describing the function. No functional change intended. Link: https://lkml.kernel.org/r/132274566cd49d2960a2294c36dd2450593dfc55.1774029655.git.ljs@kernel.org Signed-off-by: Lorenzo Stoakes (Oracle) Reviewed-by: Baolin Wang Acked-by: Qi Zheng Reviewed-by: Suren Baghdasaryan Cc: Barry Song Cc: David Hildenbrand Cc: Dev Jain Cc: Lance Yang Cc: Liam Howlett Cc: Michal Hocko Cc: Mike Rapoport Cc: Nico Pache Cc: Ryan Roberts Cc: Zi Yan Signed-off-by: Andrew Morton

mm/huge_memory: simplify vma_is_specal_huge()

2026-04-05T20:53:45+00:00

Patch series "mm/huge_memory: refactor zap_huge_pmd()", v3. zap_huge_pmd() is overly complicated, clean it up and also add an assert in the case that we encounter a buggy PMD entry that doesn't match expectations. This is motivated by a bug discovered [0] where the PMD entry was none of: * A non-DAX, PFN or mixed map. * The huge zero folio * A present PMD entry * A softleaf entry In zap_huge_pmd(), but due to the bug we manged to reach this code. It is useful to explicitly call this out rather than have an arbitrary NULL pointer dereference happen, which also improves understanding of what's going on. The series goes further to make use of vm_normal_folio_pmd() rather than implementing custom logic for retrieving the folio, and extends softleaf functionality to provide and use an equivalent softleaf function. This patch (of 13): This function is confused - it overloads the term 'special' yet again, checks for DAX but in many cases the code explicitly excludes DAX before invoking the predicate. It also unnecessarily checks for vma->vm_file - this has to be present for a driver to have set VMA_MIXEDMAP_BIT or VMA_PFNMAP_BIT. In fact, a far simpler form of this is to reverse the DAX predicate and return false if DAX is set. This makes sense from the point of view of 'special' as in vm_normal_page(), as DAX actually does potentially have retrievable folios. Also there's no need to have this in mm.h so move it to huge_memory.c. No functional change intended. Link: https://lkml.kernel.org/r/cover.1774029655.git.ljs@kernel.org Link: https://lkml.kernel.org/r/d2b65883dc4895f197c4b4a69fbf27a063463412.1774029655.git.ljs@kernel.org Link: https://lore.kernel.org/all/6b3d7ad7-49e1-407a-903d-3103704160d8@lucifer.local/ [0] Signed-off-by: Lorenzo Stoakes (Oracle) Reviewed-by: Suren Baghdasaryan Cc: Baolin Wang Cc: Barry Song Cc: David Hildenbrand Cc: Dev Jain Cc: Lance Yang Cc: Liam Howlett Cc: Michal Hocko Cc: Mike Rapoport Cc: Nico Pache Cc: Ryan Roberts Cc: Zi Yan Cc: Qi Zheng Signed-off-by: Andrew Morton

mm: introduce is_pmd_order helper

2026-04-05T20:53:29+00:00

In order to add mTHP support to khugepaged, we will often be checking if a given order is (or is not) a PMD order. Some places in the kernel already use this check, so lets create a simple helper function to keep the code clean and readable. Link: https://lkml.kernel.org/r/20260325114022.444081-3-npache@redhat.com Signed-off-by: Nico Pache Acked-by: David Hildenbrand (Arm) Reviewed-by: Baolin Wang Reviewed-by: Dev Jain Reviewed-by: Wei Yang Reviewed-by: Lance Yang Reviewed-by: Barry Song Reviewed-by: Zi Yan Reviewed-by: Pedro Falcato Reviewed-by: Lorenzo Stoakes Suggested-by: Lorenzo Stoakes Cc: Alistair Popple Cc: Andrea Arcangeli Cc: Anshuman Khandual Cc: Brendan Jackman Cc: Byungchul Park Cc: Catalin Marinas Cc: David Rientjes Cc: Gregory Price Cc: "Huang, Ying" Cc: Hugh Dickins Cc: Jan Kara Cc: Jann Horn Cc: Johannes Weiner Cc: Jonathan Corbet Cc: Joshua Hahn Cc: Kefeng Wang Cc: Liam Howlett Cc: Lorenzo Stoakes (Oracle) Cc: "Masami Hiramatsu (Google)" Cc: Mathieu Desnoyers Cc: Matthew Brost Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Mike Rapoport Cc: Nanyong Sun Cc: Peter Xu Cc: Rafael Aquini Cc: Rakie Kim Cc: Randy Dunlap Cc: Ryan Roberts Cc: Shivank Garg Cc: Steven Rostedt Cc: Suren Baghdasaryan Cc: Takashi Iwai (SUSE) Cc: Thomas Hellström Cc: Usama Arif Cc: Vishal Moola (Oracle) Cc: Vlastimil Babka Cc: Will Deacon Cc: Yang Shi Cc: Zach O'Keefe Signed-off-by: Andrew Morton

Merge tag 'mm-stable-2025-12-11-11-39' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2025-12-13T08:35:41+00:00

Pull more MM updates from Andrew Morton: - "powerpc/pseries/cmm: two smaller fixes" (David Hildenbrand) fixes a couple of minor things in ppc land - "Improve folio split related functions" (Zi Yan) some cleanups and minorish fixes in the folio splitting code * tag 'mm-stable-2025-12-11-11-39' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: mm/damon/tests/core-kunit: avoid damos_test_commit stack warning mm: vmscan: correct nr_requested tracing in scan_folios MAINTAINERS: add idr core-api doc file to XARRAY mm/hugetlb: fix incorrect error return from hugetlb_reserve_pages() mm: fix CONFIG_STACK_GROWSUP typo in mm.h mm/huge_memory: fix folio split stats counting mm/huge_memory: make min_order_for_split() always return an order mm/huge_memory: replace can_split_folio() with direct refcount calculation mm/huge_memory: change folio_split_supported() to folio_check_splittable() mm/sparse: fix sparse_vmemmap_init_nid_early definition without CONFIG_SPARSEMEM powerpc/pseries/cmm: adjust BALLOON_MIGRATE when migrating pages powerpc/pseries/cmm: call balloon_devinfo_init() also without CONFIG_BALLOON_COMPACTION

mm/huge_memory: make min_order_for_split() always return an order

2025-12-09T19:25:33+00:00

min_order_for_split() returns -EBUSY when the folio is truncated and cannot be split. In commit 77008e1b2ef7 ("mm/huge_memory: do not change split_huge_page*() target order silently"), memory_failure() does not handle it and pass -EBUSY to try_to_split_thp_page() directly. try_to_split_thp_page() returns -EINVAL since -EBUSY becomes 0xfffffff0 as new_order is unsigned int in __folio_split() and this large new_order is rejected as an invalid input. The code does not cause a bug. soft_offline_in_use_page() also uses min_order_for_split() but it always passes 0 as new_order for split. Fix it by making min_order_for_split() always return an order. When the given folio is truncated, namely folio->mapping == NULL, return 0 and let a subsequent split function handle the situation and return -EBUSY. Add kernel-doc to min_order_for_split() to clarify its use. Link: https://lkml.kernel.org/r/20251126210618.1971206-4-ziy@nvidia.com Signed-off-by: Zi Yan Reviewed-by: Wei Yang Acked-by: David Hildenbrand (Red Hat) Reviewed-by: Lorenzo Stoakes Cc: Balbir Singh Cc: Baolin Wang Cc: Barry Song Cc: Dev Jain Cc: Lance Yang Cc: Liam Howlett Cc: Miaohe Lin Cc: Naoya Horiguchi Cc: Nico Pache Cc: Ryan Roberts Signed-off-by: Andrew Morton