linux.git/mm/memory_hotplug.c, branch v7.2-rc1

drivers/base/memory: make memory block get/put explicit

2026-06-02T22:22:12+00:00

Rename the memory block lookup helper to make the acquired reference
explicit, add memory_block_put() to wrap put_device(), remove
find_memory_block(), and use memory_block_get() as the single block-id
based lookup interface.

This makes it clearer to callers that a successful lookup holds a
reference that must be dropped, reducing the chance of forgetting the
matching put and leaking the memory block device reference.

Link: https://lore.kernel.org/linux-mm/7887915D-E598-42B3-9AFE-BFFBACE8DE2D@linux.dev/#t
Link: https://lore.kernel.org/20260512072635.3969576-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song 
Acked-by: Oscar Salvador 
Acked-by: David Hildenbrand (Arm) 
Acked-by: Michal Hocko 
Tested-by: Donet Tom 
Reviewed-by: Lorenzo Stoakes 
Tested-by: Sumanth Korikkar  #s390
Cc: Richard Cheng 
Acked-by: Mike Rapoport (Microsoft) 
Cc: Alexander Gordeev 
Cc: Christian Borntraeger 
Cc: Danilo Krummrich 
Cc: Doug Anderson 
Cc: Greg Kroah-Hartman 
Cc: Heiko Carstens 
Cc: Kees Cook 
Cc: Liam R. Howlett 
Cc: Madhavan Srinivasan 
Cc: Michael Ellerman 
Cc: Nicholas Piggin 
Cc: "Rafael J. Wysocki" 
Cc: Suren Baghdasaryan 
Cc: Sven Schnelle 
Cc: Vasily Gorbik 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

mm/memory_hotplug: factor out altmap freeing checks

2026-06-02T22:22:10+00:00

Use a small helper to centralize altmap freeing after verifying that all
vmemmap pages were released.  This keeps the check consistent between the
normal teardown path and the memory hotplug error paths.

Link: https://lore.kernel.org/20260511084307.1827127-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song 
Suggested-by: David Hildenbrand (Arm) 
Acked-by: David Hildenbrand (Arm) 
Acked-by: Oscar Salvador 
Reviewed-by: Donet Tom 
Signed-off-by: Andrew Morton

mm/sparse-vmemmap: pass @pgmap argument to memory deactivation paths

2026-05-29T04:04:54+00:00

Currently, the memory hot-remove call chain -- arch_remove_memory(),
__remove_pages(), sparse_remove_section() and section_deactivate() -- does
not carry the struct dev_pagemap pointer.  This prevents the lower levels
from knowing whether the section was originally populated with vmemmap
optimizations (e.g., DAX with vmemmap optimization enabled).

Without this information, we cannot call vmemmap_can_optimize() to
determine if the vmemmap pages were optimized.  As a result, the vmemmap
page accounting during teardown will mistakenly assume a non-optimized
allocation, leading to incorrect memmap statistics.

To lay the groundwork for fixing the vmemmap page accounting, we need to
pass the @pgmap pointer down to the deactivation location.  Plumb the
@pgmap argument through the APIs of arch_remove_memory(), __remove_pages()
and sparse_remove_section(), mirroring the corresponding *_activate()
paths.

Link: https://lore.kernel.org/20260428081855.1249045-4-songmuchun@bytedance.com
Signed-off-by: Muchun Song 
Acked-by: Mike Rapoport (Microsoft) 
Reviewed-by: Oscar Salvador 
Acked-by: David Hildenbrand (Arm) 
Acked-by: Liam R. Howlett 
Cc: "Aneesh Kumar K.V" 
Cc: Joao Martins 
Cc: Lorenzo Stoakes 
Cc: Madhavan Srinivasan 
Cc: Michael Ellerman 
Cc: Michal Hocko 
Cc: Nicholas Piggin 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

mm/memory_hotplug: fix incorrect altmap passing in error path

2026-05-29T04:04:54+00:00

In create_altmaps_and_memory_blocks(), when arch_add_memory() succeeds
with memmap_on_memory enabled, the vmemmap pages are allocated from
params.altmap.  If create_memory_block_devices() subsequently fails, the
error path calls arch_remove_memory() with a NULL altmap instead of
params.altmap.

This is a bug that could lead to memory corruption.  Since altmap is NULL,
vmemmap_free() falls back to freeing the vmemmap pages into the system
buddy allocator via free_pages() instead of the altmap. 
arch_remove_memory() then immediately destroys the physical linear mapping
for this memory.  This injects unowned pages into the buddy allocator,
causing machine checks or memory corruption if the system later attempts
to allocate and use those freed pages.

Fix this by passing params.altmap to arch_remove_memory() in the error
path.

Link: https://lore.kernel.org/20260428081855.1249045-3-songmuchun@bytedance.com
Fixes: 6b8f0798b85a ("mm/memory_hotplug: split memmap_on_memory requests across memblocks")
Signed-off-by: Muchun Song 
Acked-by: David Hildenbrand (Arm) 
Acked-by: Liam R. Howlett 
Reviewed-by: Georgi Djakov 
Cc: "Aneesh Kumar K.V" 
Cc: Joao Martins 
Cc: Lorenzo Stoakes 
Cc: Madhavan Srinivasan 
Cc: Michael Ellerman 
Cc: Michal Hocko 
Cc: Mike Rapoport (Microsoft) 
Cc: Nicholas Piggin 
Cc: Oscar Salvador 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Cc: 
Signed-off-by: Andrew Morton

mm/memory_hotplug: fix memory block reference leak on remove

2026-05-14T00:40:03+00:00

Patch series "mm: Fix memory block leaks and locking", v2.

This series fixes two memory block device reference leaks and one locking
issue around the per-memory_block hwpoison counter.


This patch (of 2):

remove_memory_blocks_and_altmaps() looks up each memory block with
find_memory_block(), which acquires a reference to the memory block
device.

That reference is never dropped on this path, resulting in a leaked device
reference when removing memory blocks and their altmaps.  Drop the
reference after retrieving mem->altmap and clearing mem->altmap, before
removing the memory block device.

Link: https://lore.kernel.org/20260428085219.1316047-1-songmuchun@bytedance.com
Link: https://lore.kernel.org/20260428085219.1316047-2-songmuchun@bytedance.com
Fixes: 6b8f0798b85a ("mm/memory_hotplug: split memmap_on_memory requests across memblocks")
Signed-off-by: Muchun Song 
Acked-by: Oscar Salvador 
Acked-by: David Hildenbrand (Arm) 
Cc: Danilo Krummrich 
Cc: Greg Kroah-Hartman 
Cc: "Huang, Ying" 
Cc: Miaohe Lin 
Cc: Naoya Horiguchi 
Cc: "Rafael J. Wysocki" 
Cc: Vishal Verma 
Cc: 
Signed-off-by: Andrew Morton

Merge tag 'mm-stable-2026-04-13-21-45' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2026-04-15T19:59:16+00:00

Pull MM updates from Andrew Morton:

 - "maple_tree: Replace big node with maple copy" (Liam Howlett)

   Mainly prepararatory work for ongoing development but it does reduce
   stack usage and is an improvement.

 - "mm, swap: swap table phase III: remove swap_map" (Kairui Song)

   Offers memory savings by removing the static swap_map. It also yields
   some CPU savings and implements several cleanups.

 - "mm: memfd_luo: preserve file seals" (Pratyush Yadav)

   File seal preservation to LUO's memfd code

 - "mm: zswap: add per-memcg stat for incompressible pages" (Jiayuan
   Chen)

   Additional userspace stats reportng to zswap

 - "arch, mm: consolidate empty_zero_page" (Mike Rapoport)

   Some cleanups for our handling of ZERO_PAGE() and zero_pfn

 - "mm/kmemleak: Improve scan_should_stop() implementation" (Zhongqiu
   Han)

   A robustness improvement and some cleanups in the kmemleak code

 - "Improve khugepaged scan logic" (Vernon Yang)

   Improve khugepaged scan logic and reduce CPU consumption by
   prioritizing scanning tasks that access memory frequently

 - "Make KHO Stateless" (Jason Miu)

   Simplify Kexec Handover by transitioning KHO from an xarray-based
   metadata tracking system with serialization to a radix tree data
   structure that can be passed directly to the next kernel

 - "mm: vmscan: add PID and cgroup ID to vmscan tracepoints" (Thomas
   Ballasi and Steven Rostedt)

   Enhance vmscan's tracepointing

 - "mm: arch/shstk: Common shadow stack mapping helper and
   VM_NOHUGEPAGE" (Catalin Marinas)

   Cleanup for the shadow stack code: remove per-arch code in favour of
   a generic implementation

 - "Fix KASAN support for KHO restored vmalloc regions" (Pasha Tatashin)

   Fix a WARN() which can be emitted the KHO restores a vmalloc area

 - "mm: Remove stray references to pagevec" (Tal Zussman)

   Several cleanups, mainly udpating references to "struct pagevec",
   which became folio_batch three years ago

 - "mm: Eliminate fake head pages from vmemmap optimization" (Kiryl
   Shutsemau)

   Simplify the HugeTLB vmemmap optimization (HVO) by changing how tail
   pages encode their relationship to the head page

 - "mm/damon/core: improve DAMOS quota efficiency for core layer
   filters" (SeongJae Park)

   Improve two problematic behaviors of DAMOS that makes it less
   efficient when core layer filters are used

 - "mm/damon: strictly respect min_nr_regions" (SeongJae Park)

   Improve DAMON usability by extending the treatment of the
   min_nr_regions user-settable parameter

 - "mm/page_alloc: pcp locking cleanup" (Vlastimil Babka)

   The proper fix for a previously hotfixed SMP=n issue. Code
   simplifications and cleanups ensued

 - "mm: cleanups around unmapping / zapping" (David Hildenbrand)

   A bunch of cleanups around unmapping and zapping. Mostly
   simplifications, code movements, documentation and renaming of
   zapping functions

 - "support batched checking of the young flag for MGLRU" (Baolin Wang)

   Batched checking of the young flag for MGLRU. It's part cleanups; one
   benchmark shows large performance benefits for arm64

 - "memcg: obj stock and slab stat caching cleanups" (Johannes Weiner)

   memcg cleanup and robustness improvements

 - "Allow order zero pages in page reporting" (Yuvraj Sakshith)

   Enhance free page reporting - it is presently and undesirably order-0
   pages when reporting free memory.

 - "mm: vma flag tweaks" (Lorenzo Stoakes)

   Cleanup work following from the recent conversion of the VMA flags to
   a bitmap

 - "mm/damon: add optional debugging-purpose sanity checks" (SeongJae
   Park)

   Add some more developer-facing debug checks into DAMON core

 - "mm/damon: test and document power-of-2 min_region_sz requirement"
   (SeongJae Park)

   An additional DAMON kunit test and makes some adjustments to the
   addr_unit parameter handling

 - "mm/damon/core: make passed_sample_intervals comparisons
   overflow-safe" (SeongJae Park)

   Fix a hard-to-hit time overflow issue in DAMON core

 - "mm/damon: improve/fixup/update ratio calculation, test and
   documentation" (SeongJae Park)

   A batch of misc/minor improvements and fixups for DAMON

 - "mm: move vma_(kernel|mmu)_pagesize() out of hugetlb.c" (David
   Hildenbrand)

   Fix a possible issue with dax-device when CONFIG_HUGETLB=n. Some code
   movement was required.

 - "zram: recompression cleanups and tweaks" (Sergey Senozhatsky)

   A somewhat random mix of fixups, recompression cleanups and
   improvements in the zram code

 - "mm/damon: support multiple goal-based quota tuning algorithms"
   (SeongJae Park)

   Extend DAMOS quotas goal auto-tuning to support multiple tuning
   algorithms that users can select

 - "mm: thp: reduce unnecessary start_stop_khugepaged()" (Breno Leitao)

   Fix the khugpaged sysfs handling so we no longer spam the logs with
   reams of junk when starting/stopping khugepaged

 - "mm: improve map count checks" (Lorenzo Stoakes)

   Provide some cleanups and slight fixes in the mremap, mmap and vma
   code

 - "mm/damon: support addr_unit on default monitoring targets for
   modules" (SeongJae Park)

   Extend the use of DAMON core's addr_unit tunable

 - "mm: khugepaged cleanups and mTHP prerequisites" (Nico Pache)

   Cleanups to khugepaged and is a base for Nico's planned khugepaged
   mTHP support

 - "mm: memory hot(un)plug and SPARSEMEM cleanups" (David Hildenbrand)

   Code movement and cleanups in the memhotplug and sparsemem code

 - "mm: remove CONFIG_ARCH_ENABLE_MEMORY_HOTREMOVE and cleanup
   CONFIG_MIGRATION" (David Hildenbrand)

   Rationalize some memhotplug Kconfig support

 - "change young flag check functions to return bool" (Baolin Wang)

   Cleanups to change all young flag check functions to return bool

 - "mm/damon/sysfs: fix memory leak and NULL dereference issues" (Josh
   Law and SeongJae Park)

   Fix a few potential DAMON bugs

 - "mm/vma: convert vm_flags_t to vma_flags_t in vma code" (Lorenzo
   Stoakes)

   Convert a lot of the existing use of the legacy vm_flags_t data type
   to the new vma_flags_t type which replaces it. Mainly in the vma
   code.

 - "mm: expand mmap_prepare functionality and usage" (Lorenzo Stoakes)

   Expand the mmap_prepare functionality, which is intended to replace
   the deprecated f_op->mmap hook which has been the source of bugs and
   security issues for some time. Cleanups, documentation, extension of
   mmap_prepare into filesystem drivers

 - "mm/huge_memory: refactor zap_huge_pmd()" (Lorenzo Stoakes)

   Simplify and clean up zap_huge_pmd(). Additional cleanups around
   vm_normal_folio_pmd() and the softleaf functionality are performed.

* tag 'mm-stable-2026-04-13-21-45' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (369 commits)
  mm: fix deferred split queue races during migration
  mm/khugepaged: fix issue with tracking lock
  mm/huge_memory: add and use has_deposited_pgtable()
  mm/huge_memory: add and use normal_or_softleaf_folio_pmd()
  mm: add softleaf_is_valid_pmd_entry(), pmd_to_softleaf_folio()
  mm/huge_memory: separate out the folio part of zap_huge_pmd()
  mm/huge_memory: use mm instead of tlb->mm
  mm/huge_memory: remove unnecessary sanity checks
  mm/huge_memory: deduplicate zap deposited table call
  mm/huge_memory: remove unnecessary VM_BUG_ON_PAGE()
  mm/huge_memory: add a common exit path to zap_huge_pmd()
  mm/huge_memory: handle buggy PMD entry in zap_huge_pmd()
  mm/huge_memory: have zap_huge_pmd return a boolean, add kdoc
  mm/huge: avoid big else branch in zap_huge_pmd()
  mm/huge_memory: simplify vma_is_specal_huge()
  mm: on remap assert that input range within the proposed VMA
  mm: add mmap_action_map_kernel_pages[_full]()
  uio: replace deprecated mmap hook with mmap_prepare in uio_info
  drivers: hv: vmbus: replace deprecated mmap hook with mmap_prepare
  mm: allow handling of stacked mmap_prepare hooks in more drivers
  ...

mm/memory_hotplug: maintain N_NORMAL_MEMORY during hotplug

2026-04-06T18:13:43+00:00

N_NORMAL_MEMORY is initialized from zone population at boot, but memory
hotplug currently only updates N_MEMORY.  As a result, a node that gains
normal memory via hotplug can remain invisible to users iterating over
N_NORMAL_MEMORY, while a node that loses its last normal memory can stay
incorrectly marked as such.

The most visible effect is that
/sys/devices/system/node/has_normal_memory does not report a node even
after that node has gained normal memory via hotplug.

Also, list_lru-based shrinkers can undercount objects on such a node
and may skip reclaim on that node entirely, which can lead to a higher
memory footprint than expected.

Restore N_NORMAL_MEMORY maintenance directly in online_pages() and
offline_pages().  Set the bit when a node that currently lacks normal
memory onlines pages into a zone <= ZONE_NORMAL, and clear it when
offlining removes the last present pages from zones <= ZONE_NORMAL.

This restores the intended semantics without bringing back the old
status_change_nid_normal notifier plumbing which was removed in
8d2882a8edb8.

Current users that benefit include list_lru, zswap, nfsd filecache,
hugetlb_cgroup, and has_normal_memory sysfs reporting.

Link: https://lkml.kernel.org/r/20260330035941.518186-1-hao.li@linux.dev
Fixes: 8d2882a8edb8 ("mm,memory_hotplug: remove status_change_nid_normal and update documentation")
Signed-off-by: Hao Li 
Reviewed-by: Harry Yoo (Oracle) 
Acked-by: Vlastimil Babka (SUSE) 
Reviewed-by: Joshua Hahn 
Acked-by: David Hildenbrand (Arm) 
Cc: Oscar Salvador 
Cc: Vlastimil Babka 
Cc: 
Signed-off-by: Andrew Morton

mm/memory_hotplug: simplify check_pfn_span()

2026-04-05T20:53:31+00:00

We now always have CONFIG_SPARSEMEM_VMEMMAP, so remove the dead code.

Link: https://lkml.kernel.org/r/20260320-sparsemem_cleanups-v2-5-096addc8800d@kernel.org
Signed-off-by: David Hildenbrand (Arm) 
Reviewed-by: Lorenzo Stoakes (Oracle) 
Reviewed-by: Mike Rapoport (Microsoft) 
Cc: Axel Rasmussen 
Cc: Liam Howlett 
Cc: Michal Hocko 
Cc: Oscar Salvador 
Cc: Sidhartha Kumar 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Cc: Wei Xu 
Cc: Yuanchu Xie 
Signed-off-by: Andrew Morton

mm/memory_hotplug: remove for_each_valid_pfn() usage

2026-04-05T20:53:31+00:00

When offlining memory, we know that the memory range has no holes. 
Checking for valid pfns is not required.

Link: https://lkml.kernel.org/r/20260320-sparsemem_cleanups-v2-2-096addc8800d@kernel.org
Signed-off-by: David Hildenbrand (Arm) 
Reviewed-by: Lorenzo Stoakes (Oracle) 
Reviewed-by: Mike Rapoport (Microsoft) 
Cc: Axel Rasmussen 
Cc: Liam Howlett 
Cc: Michal Hocko 
Cc: Oscar Salvador 
Cc: Sidhartha Kumar 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Cc: Wei Xu 
Cc: Yuanchu Xie 
Signed-off-by: Andrew Morton

mm/memory_hotplug: fix possible race in scan_movable_pages()

2026-04-05T20:53:31+00:00

Patch series "mm: memory hot(un)plug and SPARSEMEM cleanups", v2.

Some cleanups around memory hot(un)plug and SPARSEMEM.  In essence, we can
limit CONFIG_MEMORY_HOTPLUG to CONFIG_SPARSEMEM_VMEMMAP, remove some dead
code, and move all the hotplug bits over to mm/sparse-vmemmap.c.

Some further/related cleanups around other unnecessary code (memory hole
handling and complicated usemap allocation).

I have some further sparse.c cleanups lying around, and I'm planning on
getting rid of bootmem_info.c entirely.


This patch (of 15):

If a hugetlb folio gets freed while we are in scan_movable_pages(),
folio_nr_pages() could return 0, resulting in or'ing "0 - 1 = -1" to the
PFN, resulting in PFN = -1.  We're not holding any locks or references
that would prevent that.

for_each_valid_pfn() would then search for the next valid PFN, and could
return a PFN that is outside of the range of the original requested range.
do_migrate_page() would then try to migrate quite a big range, which is
certainly undesirable.

To fix it, simply test for valid folio_nr_pages() values.  While at it, as
PageHuge() really just does a page_folio() internally, we can just use
folio_test_hugetlb() on the folio directly.

scan_movable_pages() is expected to be fast, and we try to avoid taking
locks or grabbing references.  We cannot use folio_try_get() as that does
not work for free hugetlb folios.  We could grab the hugetlb_lock, but
that just adds complexity.

The race is unlikely to trigger in practice, so we won't be CCing stable.

Link: https://lkml.kernel.org/r/20260320-sparsemem_cleanups-v2-0-096addc8800d@kernel.org
Link: https://lkml.kernel.org/r/20260320-sparsemem_cleanups-v2-1-096addc8800d@kernel.org
Fixes: 16540dae959d ("mm/hugetlb: mm/memory_hotplug: use a folio in scan_movable_pages()")
Signed-off-by: David Hildenbrand (Arm) 
Reviewed-by: Lorenzo Stoakes (Oracle) 
Cc: Axel Rasmussen 
Cc: Liam Howlett 
Cc: Michal Hocko 
Cc: Mike Rapoport 
Cc: Oscar Salvador 
Cc: Sidhartha Kumar 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Cc: Wei Xu 
Cc: Yuanchu Xie 
Signed-off-by: Andrew Morton