linux.git/include/linux/mmzone.h, branch v7.1-rc3

Merge tag 'mm-stable-2026-04-18-02-14' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2026-04-19T15:01:17+00:00

Pull more MM updates from Andrew Morton:

 - "Eliminate Dying Memory Cgroup" (Qi Zheng and Muchun Song)

   Address the longstanding "dying memcg problem". A situation wherein a
   no-longer-used memory control group will hang around for an extended
   period pointlessly consuming memory

 - "fix unexpected type conversions and potential overflows" (Qi Zheng)

   Fix a couple of potential 32-bit/64-bit issues which were identified
   during review of the "Eliminate Dying Memory Cgroup" series

 - "kho: history: track previous kernel version and kexec boot count"
   (Breno Leitao)

   Use Kexec Handover (KHO) to pass the previous kernel's version string
   and the number of kexec reboots since the last cold boot to the next
   kernel, and print it at boot time

 - "liveupdate: prevent double preservation" (Pasha Tatashin)

   Teach LUO to avoid managing the same file across different active
   sessions

 - "liveupdate: Fix module unloading and unregister API" (Pasha
   Tatashin)

   Address an issue with how LUO handles module reference counting and
   unregistration during module unloading

 - "zswap pool per-CPU acomp_ctx simplifications" (Kanchana Sridhar)

   Simplify and clean up the zswap crypto compression handling and
   improve the lifecycle management of zswap pool's per-CPU acomp_ctx
   resources

 - "mm/damon/core: fix damon_call()/damos_walk() vs kdmond exit race"
   (SeongJae Park)

   Address unlikely but possible leaks and deadlocks in damon_call() and
   damon_walk()

 - "mm/damon/core: validate damos_quota_goal->nid" (SeongJae Park)

   Fix a couple of root-only wild pointer dereferences

 - "Docs/admin-guide/mm/damon: warn commit_inputs vs other params race"
   (SeongJae Park)

   Update the DAMON documentation to warn operators about potential
   races which can occur if the commit_inputs parameter is altered at
   the wrong time

 - "Minor hmm_test fixes and cleanups" (Alistair Popple)

   Bugfixes and a cleanup for the HMM kernel selftests

 - "Modify memfd_luo code" (Chenghao Duan)

   Cleanups, simplifications and speedups to the memfd_lou code

 - "mm, kvm: allow uffd support in guest_memfd" (Mike Rapoport)

   Support for userfaultfd in guest_memfd

 - "selftests/mm: skip several tests when thp is not available" (Chunyu
   Hu)

   Fix several issues in the selftests code which were causing breakage
   when the tests were run on CONFIG_THP=n kernels

 - "mm/mprotect: micro-optimization work" (Pedro Falcato)

   A couple of nice speedups for mprotect()

 - "MAINTAINERS: update KHO and LIVE UPDATE entries" (Pratyush Yadav)

   Document upcoming changes in the maintenance of KHO, LUO, memfd_luo,
   kexec, crash, kdump and probably other kexec-based things - they are
   being moved out of mm.git and into a new git tree

* tag 'mm-stable-2026-04-18-02-14' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (121 commits)
  MAINTAINERS: add page cache reviewer
  mm/vmscan: avoid false-positive -Wuninitialized warning
  MAINTAINERS: update Dave's kdump reviewer email address
  MAINTAINERS: drop include/linux/liveupdate from LIVE UPDATE
  MAINTAINERS: drop include/linux/kho/abi/ from KHO
  MAINTAINERS: update KHO and LIVE UPDATE maintainers
  MAINTAINERS: update kexec/kdump maintainers entries
  mm/migrate_device: remove dead migration entry check in migrate_vma_collect_huge_pmd()
  selftests: mm: skip charge_reserved_hugetlb without killall
  userfaultfd: allow registration of ranges below mmap_min_addr
  mm/vmstat: fix vmstat_shepherd double-scheduling vmstat_update
  mm/hugetlb: fix early boot crash on parameters without '=' separator
  zram: reject unrecognized type= values in recompress_store()
  docs: proc: document ProtectionKey in smaps
  mm/mprotect: special-case small folios when applying permissions
  mm/mprotect: move softleaf code out of the main function
  mm: remove '!root_reclaim' checking in should_abort_scan()
  mm/sparse: fix comment for section map alignment
  mm/page_io: use sio->len for PSWPIN accounting in sio_read_complete()
  selftests/mm: transhuge_stress: skip the test when thp not available
  ...

mm/sparse: fix comment for section map alignment

2026-04-18T07:10:55+00:00

The comment in mmzone.h currently details exhaustive per-architecture
bit-width lists and explains alignment using min(PAGE_SHIFT,
PFN_SECTION_SHIFT).  Such details risk falling out of date over time and
may inadvertently be left un-updated.

We always expect a single section to cover full pages.  Therefore, we can
safely assume that PFN_SECTION_SHIFT is large enough to accommodate
SECTION_MAP_LAST_BIT.  We use BUILD_BUG_ON() to ensure this.

Update the comment to accurately reflect this consensus, making it clear
that we rely on a single section covering full pages.

Link: https://lore.kernel.org/20260402102320.3617578-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song 
Acked-by: David Hildenbrand (Arm) 
Cc: Liam Howlett 
Cc: Lorenzo Stoakes (Oracle) 
Cc: Michal Hocko 
Cc: Mike Rapoport 
Cc: Petr Tesarik 
Cc: Suren Baghdasaryan 
Signed-off-by: Andrew Morton

mm: vmscan: prepare for reparenting MGLRU folios

2026-04-18T07:10:47+00:00

Similar to traditional LRU folios, in order to solve the dying memcg
problem, we also need to reparenting MGLRU folios to the parent memcg when
memcg offline.

However, there are the following challenges:

1. Each lruvec has between MIN_NR_GENS and MAX_NR_GENS generations, the
   number of generations of the parent and child memcg may be different,
   so we cannot simply transfer MGLRU folios in the child memcg to the
   parent memcg as we did for traditional LRU folios.
2. The generation information is stored in folio->flags, but we cannot
   traverse these folios while holding the lru lock, otherwise it may
   cause softlockup.
3. In walk_update_folio(), the gen of folio and corresponding lru size
   may be updated, but the folio is not immediately moved to the
   corresponding lru list. Therefore, there may be folios of different
   generations on an LRU list.
4. In lru_gen_del_folio(), the generation to which the folio belongs is
   found based on the generation information in folio->flags, and the
   corresponding LRU size will be updated. Therefore, we need to update
   the lru size correctly during reparenting, otherwise the lru size may
   be updated incorrectly in lru_gen_del_folio().

Finally, this patch chose a compromise method, which is to splice the lru
list in the child memcg to the lru list of the same generation in the
parent memcg during reparenting.  And in order to ensure that the parent
memcg has the same generation, we need to increase the generations in the
parent memcg to the MAX_NR_GENS before reparenting.

Of course, the same generation has different meanings in the parent and
child memcg, this will cause confusion in the hot and cold information of
folios.  But other than that, this method is simple enough, the lru size
is correct, and there is no need to consider some concurrency issues (such
as lru_gen_del_folio()).

To prepare for the above work, this commit implements the specific
functions, which will be used during reparenting.

[zhengqi.arch@bytedance.com: use list_splice_tail_init() to reparent child folios]
  Link: https://lore.kernel.org/20260324114937.28569-1-qi.zheng@linux.dev
Link: https://lore.kernel.org/e75050354cdbc42221a04f7cf133292b61105548.1772711148.git.zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng 
Suggested-by: Harry Yoo 
Suggested-by: Imran Khan 
Acked-by: Harry Yoo 
Cc: Allen Pais 
Cc: Axel Rasmussen 
Cc: Baoquan He 
Cc: Chengming Zhou 
Cc: Chen Ridong 
Cc: David Hildenbrand 
Cc: Hamza Mahfooz 
Cc: Hugh Dickins 
Cc: Johannes Weiner 
Cc: Kamalesh Babulal 
Cc: Lance Yang 
Cc: Liam Howlett 
Cc: Lorenzo Stoakes (Oracle) 
Cc: Michal Hocko 
Cc: Michal Koutný 
Cc: Mike Rapoport 
Cc: Muchun Song 
Cc: Muchun Song 
Cc: Nhat Pham 
Cc: Roman Gushchin 
Cc: Shakeel Butt 
Cc: Suren Baghdasaryan 
Cc: Usama Arif 
Cc: Vlastimil Babka 
Cc: Wei Xu 
Cc: Yosry Ahmed 
Cc: Yuanchu Xie 
Cc: Zi Yan 
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: add gpu active/reclaim per-node stat counters (v2)

2026-04-07T20:52:47+00:00

While discussing memcg intergration with gpu memory allocations,
it was pointed out that there was no numa/system counters for
GPU memory allocations.

With more integrated memory GPU server systems turning up, and
more requirements for memory tracking it seems we should start
closing the gap.

Add two counters to track GPU per-node system memory allocations.

The first is currently allocated to GPU objects, and the second
is for memory that is stored in GPU page pools that can be reclaimed,
by the shrinker.

Cc: Christian Koenig 
Cc: Matthew Brost 
Cc: Johannes Weiner 
Cc: linux-mm@kvack.org
Cc: Andrew Morton 
Acked-by: Zi Yan 
Acked-by: Shakeel Butt 
Acked-by: Andrew Morton 
Acked-by: Christian König 
Signed-off-by: Dave Airlie

mm/sparse: move memory hotplug bits to sparse-vmemmap.c

2026-04-05T20:53:33+00:00

Let's move all memory hoptplug related code to sparse-vmemmap.c.

We only have to expose sparse_index_init().  While at it, drop the
definition of sparse_index_init() for !CONFIG_SPARSEMEM, which is unused,
and place the declaration in internal.h.

Link: https://lkml.kernel.org/r/20260320-sparsemem_cleanups-v2-15-096addc8800d@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/sparse: move sparse_init_one_section() to internal.h

2026-04-05T20:53:33+00:00

While at it, convert the BUG_ON to a VM_WARN_ON_ONCE, avoid long lines,
and merge sparse_encode_mem_map() into its only caller
sparse_init_one_section().

Clarify the comment a bit, pointing at page_to_pfn().

[david@kernel.org: s/VM_WARN_ON/VM_WARN_ON_ONCE/]
  Link: https://lkml.kernel.org/r/6b04c1a1-74e7-42e8-8523-a40802e5dacc@kernel.org
Link: https://lkml.kernel.org/r/20260320-sparsemem_cleanups-v2-13-096addc8800d@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: prepare to move subsection_map_init() to mm/sparse-vmemmap.c

2026-04-05T20:53:32+00:00

We want to move subsection_map_init() to mm/sparse-vmemmap.c.

To prepare for getting rid of subsection_map_init() in mm/sparse.c
completely, use a static inline function for !CONFIG_SPARSEMEM_VMEMMAP.

While at it, move the declaration to internal.h and rename it to
"sparse_init_subsection_map()".

Link: https://lkml.kernel.org/r/20260320-sparsemem_cleanups-v2-11-096addc8800d@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: support batched checking of the young flag for MGLRU

2026-04-05T20:53:16+00:00

Use the batched helper test_and_clear_young_ptes_notify() to check and
clear the young flag to improve the performance during large folio
reclamation when MGLRU is enabled.

Meanwhile, we can also support batched checking the young and dirty flag
when MGLRU walks the mm's pagetable to update the folios' generation
counter.  Since MGLRU also checks the PTE dirty bit, use
folio_pte_batch_flags() with FPB_MERGE_YOUNG_DIRTY set to detect batches
of PTEs for a large folio.

Then we can remove the ptep_test_and_clear_young_notify() since it has no
users now.

Note that we also update the 'young' counter and 'mm_stats[MM_LEAF_YOUNG]'
counter with the batched count in the lru_gen_look_around() and
walk_pte_range().  However, the batched operations may inflate these two
counters, because in a large folio not all PTEs may have been accessed. 
(Additionally, tracking how many PTEs have been accessed within a large
folio is not very meaningful, since the mm core actually tracks
access/dirty on a per-folio basis, not per page).  The impact analysis is
as follows:

1. The 'mm_stats[MM_LEAF_YOUNG]' counter has no functional impact and
   is mainly for debugging.

2. The 'young' counter is used to decide whether to place the current
   PMD entry into the bloom filters by suitable_to_scan() (so that next
   time we can check whether it has been accessed again), which may set
   the hash bit in the bloom filters for a PMD entry that hasn't seen much
   access.  However, bloom filters inherently allow some error, so this
   effect appears negligible.

Link: https://lkml.kernel.org/r/378f4acf7d07410aa7c2e4b49d56bb165918eb34.1772778858.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang 
Reviewed-by: Rik van Riel 
Acked-by: David Hildenbrand (Arm) 
Cc: Alistair Popple 
Cc: Axel Rasmussen 
Cc: Barry Song 
Cc: Catalin Marinas 
Cc: Dev Jain 
Cc: Jann Horn 
Cc: Johannes Weiner 
Cc: Liam Howlett 
Cc: Lorenzo Stoakes (Oracle) 
Cc: Matthew Wilcox (Oracle) 
Cc: Michal Hocko 
Cc: Mike Rapoport 
Cc: Qi Zheng 
Cc: Ryan Roberts 
Cc: Shakeel Butt 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Cc: Wei Xu 
Cc: Will Deacon 
Cc: Yuanchu Xie 
Signed-off-by: Andrew Morton

mm/hugetlb: remove fake head pages

2026-04-05T20:53:09+00:00

HugeTLB Vmemmap Optimization (HVO) reduces memory usage by freeing most
vmemmap pages for huge pages and remapping the freed range to a single
page containing the struct page metadata.

With the new mask-based compound_info encoding (for power-of-2 struct page
sizes), all tail pages of the same order are now identical regardless of
which compound page they belong to.  This means the tail pages can be
truly shared without fake heads.

Allocate a single page of initialized tail struct pages per zone per order
in the vmemmap_tails[] array in struct zone.  All huge pages of that order
in the zone share this tail page, mapped read-only into their vmemmap. 
The head page remains unique per huge page.

Redefine MAX_FOLIO_ORDER using ilog2().  The define has to produce a
compile-constant as it is used to specify vmemmap_tail array size.  For
some reason, compiler is not able to solve get_order() at compile-time,
but ilog2() works.

Avoid PUD_ORDER to define MAX_FOLIO_ORDER as it adds dependency to
 which generates hard-to-break include loop.

This eliminates fake heads while maintaining the same memory savings, and
simplifies compound_head() by removing fake head detection.

Link: https://lkml.kernel.org/r/20260227194302.274384-13-kas@kernel.org
Signed-off-by: Kiryl Shutsemau 
Reviewed-by: Vlastimil Babka (SUSE) 
Acked-by: David Hildenbrand (Arm) 
Cc: Albert Ou 
Cc: Alexandre Ghiti 
Cc: Baoquan He 
Cc: Christoph Lameter 
Cc: David Rientjes 
Cc: Frank van der Linden 
Cc: Harry Yoo 
Cc: Huacai Chen 
Cc: Johannes Weiner 
Cc: Jonathan Corbet 
Cc: Lorenzo Stoakes 
Cc: Matthew Wilcox (Oracle) 
Cc: Michal Hocko 
Cc: Mike Rapoport 
Cc: Muchun Song 
Cc: Oscar Salvador 
Cc: Palmer Dabbelt 
Cc: Paul Walmsley 
Cc: Roman Gushchin 
Cc: Usama Arif 
Cc: WANG Xuerui 
Cc: Zi Yan 
Signed-off-by: Andrew Morton