Merge tag 'mm-stable-2022-08-09' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull remaining MM updates from Andrew Morton:
"Three patch series - two that perform cleanups and one feature:

- hugetlb_vmemmap cleanups from Muchun Song

- hardware poisoning support for 1GB hugepages, from Naoya Horiguchi

- highmem documentation fixups from Fabio De Francesco"

* tag 'mm-stable-2022-08-09' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (23 commits)
Documentation/mm: add details about kmap_local_page() and preemption
highmem: delete a sentence from kmap_local_page() kdocs
Documentation/mm: rrefer kmap_local_page() and avoid kmap()
Documentation/mm: avoid invalid use of addresses from kmap_local_page()
Documentation/mm: don't kmap*() pages which can't come from HIGHMEM
highmem: specify that kmap_local_page() is callable from interrupts
highmem: remove unneeded spaces in kmap_local_page() kdocs
mm, hwpoison: enable memory error handling on 1GB hugepage
mm, hwpoison: skip raw hwpoison page in freeing 1GB hugepage
mm, hwpoison: make __page_handle_poison returns int
mm, hwpoison: set PG_hwpoison for busy hugetlb pages
mm, hwpoison: make unpoison aware of raw error info in hwpoisoned hugepage
mm, hwpoison, hugetlb: support saving mechanism of raw error pages
mm/hugetlb: make pud_huge() and follow_huge_pud() aware of non-present pud entry
mm/hugetlb: check gigantic_page_runtime_supported() in return_unused_surplus_pages()
mm: hugetlb_vmemmap: use PTRS_PER_PTE instead of PMD_SIZE / PAGE_SIZE
mm: hugetlb_vmemmap: move code comments to vmemmap_dedup.rst
mm: hugetlb_vmemmap: improve hugetlb_vmemmap code readability
mm: hugetlb_vmemmap: replace early_param() with core_param()
mm: hugetlb_vmemmap: move vmemmap code related to HugeTLB to hugetlb_vmemmap.c
...

Documentation/admin-guide/kernel-parameters.txt

···
 	hugetlb_free_vmemmap=
 			[KNL] Reguires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 			enabled.
+			Control if HugeTLB Vmemmap Optimization (HVO) is enabled.
 			Allows heavy hugetlb users to free up some more
 			memory (7 * PAGE_SIZE for each 2MB hugetlb page).
-			Format: { [oO][Nn]/Y/y/1 | [oO][Ff]/N/n/0 (default) }
+			Format: { on | off (default) }
 
-			[oO][Nn]/Y/y/1: enable the feature
-			[oO][Ff]/N/n/0: disable the feature
+			on: enable HVO
+			off: disable HVO
 
 			Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
 			the default is on.

Documentation/admin-guide/mm/hugetlbpage.rst

···
 	will all result in 256 2M huge pages being allocated.  Valid default
 	huge page size is architecture dependent.
 hugetlb_free_vmemmap
-	When CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is set, this enables optimizing
-	unused vmemmap pages associated with each HugeTLB page.
+	When CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is set, this enables HugeTLB
+	Vmemmap Optimization (HVO).
 
 When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages``
 indicates the current number of pre-allocated huge pages of the default size.

Documentation/admin-guide/mm/memory-hotplug.rst

···
 - Concurrent activity that operates on the same physical memory area, such as
   allocating gigantic pages, can result in temporary offlining failures.
 
-- Out of memory when dissolving huge pages, especially when freeing unused
-  vmemmap pages associated with each hugetlb page is enabled.
+- Out of memory when dissolving huge pages, especially when HugeTLB Vmemmap
+  Optimization (HVO) is enabled.
 
   Offlining code may be able to migrate huge page contents, but may not be able
   to dissolve the source huge page because it fails allocating (unmovable) pages

Documentation/admin-guide/sysctl/vm.rst

···
 in include/linux/mm_types.h) is not power of two (an unusual system config could
 result in this).
 
-Enable (set to 1) or disable (set to 0) the feature of optimizing vmemmap pages
-associated with each HugeTLB page.
+Enable (set to 1) or disable (set to 0) HugeTLB Vmemmap Optimization (HVO).
 
 Once enabled, the vmemmap pages of subsequent allocation of HugeTLB pages from
 buddy allocator will be optimized (7 pages per 2MB HugeTLB page and 4095 pages

Documentation/mm/highmem.rst

···
   This function should be preferred, where feasible, over all the others.
 
   These mappings are thread-local and CPU-local, meaning that the mapping
-  can only be accessed from within this thread and the thread is bound the
-  CPU while the mapping is active. Even if the thread is preempted (since
-  preemption is never disabled by the function) the CPU can not be
-  unplugged from the system via CPU-hotplug until the mapping is disposed.
+  can only be accessed from within this thread and the thread is bound to the
+  CPU while the mapping is active. Although preemption is never disabled by
+  this function, the CPU can not be unplugged from the system via
+  CPU-hotplug until the mapping is disposed.
 
   It's valid to take pagefaults in a local kmap region, unless the context
   in which the local mapping is acquired does not allow it for other reasons.
 
+  As said, pagefaults and preemption are never disabled. There is no need to
+  disable preemption because, when context switches to a different task, the
+  maps of the outgoing task are saved and those of the incoming one are
+  restored.
+
   kmap_local_page() always returns a valid virtual address and it is assumed
   that kunmap_local() will never fail.
+
+  On CONFIG_HIGHMEM=n kernels and for low memory pages this returns the
+  virtual address of the direct mapping. Only real highmem pages are
+  temporarily mapped. Therefore, users may call a plain page_address()
+  for pages which are known to not come from ZONE_HIGHMEM. However, it is
+  always safe to use kmap_local_page() / kunmap_local().
+
+  While it is significantly faster than kmap(), for the higmem case it
+  comes with restrictions about the pointers validity. Contrary to kmap()
+  mappings, the local mappings are only valid in the context of the caller
+  and cannot be handed to other contexts. This implies that users must
+  be absolutely sure to keep the use of the return address local to the
+  thread which mapped it.
+
+  Most code can be designed to use thread local mappings. User should
+  therefore try to design their code to avoid the use of kmap() by mapping
+  pages in the same thread the address will be used and prefer
+  kmap_local_page().
 
   Nesting kmap_local_page() and kmap_atomic() mappings is allowed to a certain
   extent (up to KMAP_TYPE_NR) but their invocations have to be strictly ordered

Documentation/mm/vmemmap_dedup.rst

···
 HugeTLB
 =======
 
-The struct page structures (page structs) are used to describe a physical
-page frame. By default, there is a one-to-one mapping from a page frame to
-it's corresponding page struct.
+This section is to explain how HugeTLB Vmemmap Optimization (HVO) works.
+
+The ``struct page`` structures are used to describe a physical page frame. By
+default, there is a one-to-one mapping from a page frame to it's corresponding
+``struct page``.
 
 HugeTLB pages consist of multiple base page size pages and is supported by many
 architectures. See Documentation/admin-guide/mm/hugetlbpage.rst for more
 details. On the x86-64 architecture, HugeTLB pages of size 2MB and 1GB are
 currently supported. Since the base page size on x86 is 4KB, a 2MB HugeTLB page
 consists of 512 base pages and a 1GB HugeTLB page consists of 4096 base pages.
-For each base page, there is a corresponding page struct.
+For each base page, there is a corresponding ``struct page``.
 
-Within the HugeTLB subsystem, only the first 4 page structs are used to
-contain unique information about a HugeTLB page. __NR_USED_SUBPAGE provides
-this upper limit. The only 'useful' information in the remaining page structs
+Within the HugeTLB subsystem, only the first 4 ``struct page`` are used to
+contain unique information about a HugeTLB page. ``__NR_USED_SUBPAGE`` provides
+this upper limit. The only 'useful' information in the remaining ``struct page``
 is the compound_head field, and this field is the same for all tail pages.
 
-By removing redundant page structs for HugeTLB pages, memory can be returned
+By removing redundant ``struct page`` for HugeTLB pages, memory can be returned
 to the buddy allocator for other uses.
 
 Different architectures support different HugeTLB pages. For example, the
···
 |              |   64KB    |    2MB    |  512MB    |    16GB   |           |
 +--------------+-----------+-----------+-----------+-----------+-----------+
 
-When the system boot up, every HugeTLB page has more than one struct page
+When the system boot up, every HugeTLB page has more than one ``struct page``
 structs which size is (unit: pages)::
 
    struct_size = HugeTLB_Size / PAGE_SIZE * sizeof(struct page) / PAGE_SIZE
···
 n is (PAGE_SIZE / sizeof(pte_t)).
 
 This optimization only supports 64-bit system, so the value of sizeof(pte_t)
-is 8. And this optimization also applicable only when the size of struct page
-is a power of two. In most cases, the size of struct page is 64 bytes (e.g.
+is 8. And this optimization also applicable only when the size of ``struct page``
+is a power of two. In most cases, the size of ``struct page`` is 64 bytes (e.g.
 x86-64 and arm64). So if we use pmd level mapping for a HugeTLB page, the
-size of struct page structs of it is 8 page frames which size depends on the
+size of ``struct page`` structs of it is 8 page frames which size depends on the
 size of the base page.
 
 For the HugeTLB page of the pud level mapping, then::
···
                = PAGE_SIZE / 8 * 8 (pages)
                = PAGE_SIZE (pages)
 
-Where the struct_size(pmd) is the size of the struct page structs of a
+Where the struct_size(pmd) is the size of the ``struct page`` structs of a
 HugeTLB page of the pmd level mapping.
 
 E.g.: A 2MB HugeTLB page on x86_64 consists in 8 page frames while 1GB
···
 
 Next, we take the pmd level mapping of the HugeTLB page as an example to
 show the internal implementation of this optimization. There are 8 pages
-struct page structs associated with a HugeTLB page which is pmd mapped.
+``struct page`` structs associated with a HugeTLB page which is pmd mapped.
 
 Here is how things look before optimization::
 
···
  +-----------+
 
 The value of page->compound_head is the same for all tail pages. The first
-page of page structs (page 0) associated with the HugeTLB page contains the 4
-page structs necessary to describe the HugeTLB. The only use of the remaining
-pages of page structs (page 1 to page 7) is to point to page->compound_head.
-Therefore, we can remap pages 1 to 7 to page 0. Only 1 page of page structs
+page of ``struct page`` (page 0) associated with the HugeTLB page contains the 4
+``struct page`` necessary to describe the HugeTLB. The only use of the remaining
+pages of ``struct page`` (page 1 to page 7) is to point to page->compound_head.
+Therefore, we can remap pages 1 to 7 to page 0. Only 1 page of ``struct page``
 will be used for each HugeTLB page. This will allow us to free the remaining
 7 pages to the buddy allocator.
 
···
 
 The contiguous bit is used to increase the mapping size at the pmd and pte
 (last) level. So this type of HugeTLB page can be optimized only when its
-size of the struct page structs is greater than 1 page.
+size of the ``struct page`` structs is greater than **1** page.
 
 Notice: The head vmemmap page is not freed to the buddy allocator and all
 tail vmemmap pages are mapped to the head vmemmap page frame. So we can see
-more than one struct page struct with PG_head (e.g. 8 per 2 MB HugeTLB page)
-associated with each HugeTLB page. The compound_head() can handle this
-correctly (more details refer to the comment above compound_head()).
+more than one ``struct page`` struct with ``PG_head`` (e.g. 8 per 2 MB HugeTLB
+page) associated with each HugeTLB page. The ``compound_head()`` can handle
+this correctly. There is only **one** head ``struct page``, the tail
+``struct page`` with ``PG_head`` are fake head ``struct page``.  We need an
+approach to distinguish between those two different types of ``struct page`` so
+that ``compound_head()`` can return the real head ``struct page`` when the
+parameter is the tail ``struct page`` but with ``PG_head``. The following code
+snippet describes how to distinguish between real and fake head ``struct page``.
+
+.. code-block:: c
+
+	if (test_bit(PG_head, &page->flags)) {
+		unsigned long head = READ_ONCE(page[1].compound_head);
+
+		if (head & 1) {
+			if (head == (unsigned long)page + 1)
+				/* head struct page */
+			else
+				/* tail struct page */
+		} else {
+			/* head struct page */
+		}
+	}
+
+We can safely access the field of the **page[1]** with ``PG_head`` because the
+page is a compound page composed with at least two contiguous pages.
+The implementation refers to ``page_fixed_fake_head()``.
 
 Device DAX
 ==========
···
 
 The differences with HugeTLB are relatively minor.
 
-It only use 3 page structs for storing all information as opposed
+It only use 3 ``struct page`` for storing all information as opposed
 to 4 on HugeTLB pages.
 
 There's no remapping of vmemmap given that device-dax memory is not part of

arch/arm64/mm/flush.c

···
 void flush_dcache_page(struct page *page)
 {
 	/*
-	 * Only the head page's flags of HugeTLB can be cleared since the tail
-	 * vmemmap pages associated with each HugeTLB page are mapped with
-	 * read-only when CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is enabled (more
-	 * details can refer to vmemmap_remap_pte()).  Although
-	 * __sync_icache_dcache() only set PG_dcache_clean flag on the head
-	 * page struct, there is more than one page struct with PG_dcache_clean
-	 * associated with the HugeTLB page since the head vmemmap page frame
-	 * is reused (more details can refer to the comments above
-	 * page_fixed_fake_head()).
+	 * HugeTLB pages are always fully mapped and only head page will be
+	 * set PG_dcache_clean (see comments in __sync_icache_dcache()).
 	 */
-	if (hugetlb_optimize_vmemmap_enabled() && PageHuge(page))
+	if (PageHuge(page))
 		page = compound_head(page);
 
 	if (test_bit(PG_dcache_clean, &page->flags))

arch/x86/mm/hugetlbpage.c

···
 		(pmd_val(pmd) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT;
 }
 
+/*
+ * pud_huge() returns 1 if @pud is hugetlb related entry, that is normal
+ * hugetlb entry or non-present (migration or hwpoisoned) hugetlb entry.
+ * Otherwise, returns 0.
+ */
 int pud_huge(pud_t pud)
 {
-	return !!(pud_val(pud) & _PAGE_PSE);
+	return !pud_none(pud) &&
+		(pud_val(pud) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT;
 }
 
 #ifdef CONFIG_HUGETLB_PAGE

fs/Kconfig

···
 
 #
 # Select this config option from the architecture Kconfig, if it is preferred
-# to enable the feature of minimizing overhead of struct page associated with
-# each HugeTLB page.
+# to enable the feature of HugeTLB Vmemmap Optimization (HVO).
 #
 config ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	bool
···
 	depends on SPARSEMEM_VMEMMAP
 
 config HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON
-	bool "Default optimizing vmemmap pages of HugeTLB to on"
+	bool "HugeTLB Vmemmap Optimization (HVO) defaults to on"
 	default n
 	depends on HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	help
-	  When using HUGETLB_PAGE_OPTIMIZE_VMEMMAP, the optimizing unused vmemmap
-	  pages associated with each HugeTLB page is default off. Say Y here
-	  to enable optimizing vmemmap pages of HugeTLB by default. It can then
-	  be disabled on the command line via hugetlb_free_vmemmap=off.
+	  The HugeTLB VmemmapvOptimization (HVO) defaults to off. Say Y here to
+	  enable HVO by default. It can be disabled via hugetlb_free_vmemmap=off
+	  (boot command line) or hugetlb_optimize_vmemmap (sysctl).
 
 config MEMFD_CREATE
 	def_bool TMPFS || HUGETLBFS

include/linux/highmem.h

···
 
 /**
  * kmap_local_page - Map a page for temporary usage
- * @page:	Pointer to the page to be mapped
+ * @page: Pointer to the page to be mapped
  *
  * Returns: The virtual address of the mapping
  *
- * Can be invoked from any context.
+ * Can be invoked from any context, including interrupts.
  *
  * Requires careful handling when nesting multiple mappings because the map
  * management is stack based. The unmap has to be in the reverse order of
···
  * temporarily mapped.
  *
  * While it is significantly faster than kmap() for the higmem case it
- * comes with restrictions about the pointer validity. Only use when really
- * necessary.
+ * comes with restrictions about the pointer validity.
  *
  * On HIGHMEM enabled systems mapping a highmem page has the side effect of
  * disabling migration in order to keep the virtual address stable across

include/linux/hugetlb.h

···
 	SUBPAGE_INDEX_CGROUP_RSVD,	/* reuse page->private */
 	__MAX_CGROUP_SUBPAGE_INDEX = SUBPAGE_INDEX_CGROUP_RSVD,
 #endif
+#ifdef CONFIG_MEMORY_FAILURE
+	SUBPAGE_INDEX_HWPOISON,
+#endif
 	__NR_USED_SUBPAGE,
 };
 
···
  *	Synchronization:  Initially set after new page allocation with no
  *	locking.  When examined and modified during migration processing
  *	(isolate, migrate, putback) the hugetlb_lock is held.
- * HPG_temporary - - Set on a page that is temporarily allocated from the buddy
+ * HPG_temporary - Set on a page that is temporarily allocated from the buddy
  *	allocator.  Typically used for migration target pages when no pages
  *	are available in the pool.  The hugetlb free page path will
  *	immediately free pages with this flag set to the buddy allocator.
···
  * HPG_freed - Set when page is on the free lists.
  *	Synchronization: hugetlb_lock held for examination and modification.
  * HPG_vmemmap_optimized - Set when the vmemmap pages of the page are freed.
+ * HPG_raw_hwp_unreliable - Set when the hugetlb page has a hwpoison sub-page
+ *     that is not tracked by raw_hwp_page list.
  */
 enum hugetlb_page_flags {
 	HPG_restore_reserve = 0,
···
 	HPG_temporary,
 	HPG_freed,
 	HPG_vmemmap_optimized,
+	HPG_raw_hwp_unreliable,
 	__NR_HPAGEFLAGS,
 };
 
···
 HPAGEFLAG(Temporary, temporary)
 HPAGEFLAG(Freed, freed)
 HPAGEFLAG(VmemmapOptimized, vmemmap_optimized)
+HPAGEFLAG(RawHwpUnreliable, raw_hwp_unreliable)
 
 #ifdef CONFIG_HUGETLB_PAGE
 
···
 	unsigned int nr_huge_pages_node[MAX_NUMNODES];
 	unsigned int free_huge_pages_node[MAX_NUMNODES];
 	unsigned int surplus_huge_pages_node[MAX_NUMNODES];
-#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
-	unsigned int optimize_vmemmap_pages;
-#endif
 #ifdef CONFIG_CGROUP_HUGETLB
 	/* cgroup control files */
 	struct cftype cgroup_files_dfl[8];
···
 	return hstate_file(vma->vm_file);
 }
 
-static inline unsigned long huge_page_size(struct hstate *h)
+static inline unsigned long huge_page_size(const struct hstate *h)
 {
 	return (unsigned long)PAGE_SIZE << h->order;
 }
···
 	return huge_page_order(h) >= MAX_ORDER;
 }
 
-static inline unsigned int pages_per_huge_page(struct hstate *h)
+static inline unsigned int pages_per_huge_page(const struct hstate *h)
 {
 	return 1 << h->order;
 }
···
 extern int dissolve_free_huge_page(struct page *page);
 extern int dissolve_free_huge_pages(unsigned long start_pfn,
 				    unsigned long end_pfn);
+
+#ifdef CONFIG_MEMORY_FAILURE
+extern void hugetlb_clear_page_hwpoison(struct page *hpage);
+#else
+static inline void hugetlb_clear_page_hwpoison(struct page *hpage)
+{
+}
+#endif
 
 #ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
 #ifndef arch_hugetlb_migration_supported

include/linux/mm.h

···
 }
 #endif
 
-#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
-int vmemmap_remap_free(unsigned long start, unsigned long end,
-		       unsigned long reuse);
-int vmemmap_remap_alloc(unsigned long start, unsigned long end,
-			unsigned long reuse, gfp_t gfp_mask);
-#endif
-
 void *sparse_buffer_alloc(unsigned long size);
 struct page * __populate_section_memmap(unsigned long pfn,
 		unsigned long nr_pages, int nid, struct vmem_altmap *altmap,
···
 	MF_SOFT_OFFLINE = 1 << 3,
 	MF_UNPOISON = 1 << 4,
 	MF_SW_SIMULATED = 1 << 5,
+	MF_NO_RETRY = 1 << 6,
 };
 int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
 		      unsigned long count, int mf_flags);
···
 	MF_MSG_DIFFERENT_COMPOUND,
 	MF_MSG_HUGE,
 	MF_MSG_FREE_HUGE,
-	MF_MSG_NON_PMD_HUGE,
 	MF_MSG_UNMAP_FAILED,
 	MF_MSG_DIRTY_SWAPCACHE,
 	MF_MSG_CLEAN_SWAPCACHE,

include/linux/page-flags.h

···
 #ifndef __GENERATING_BOUNDS_H
 
 #ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
-DECLARE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
-			 hugetlb_optimize_vmemmap_key);
-
-static __always_inline bool hugetlb_optimize_vmemmap_enabled(void)
-{
-	return static_branch_maybe(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
-				   &hugetlb_optimize_vmemmap_key);
-}
+DECLARE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key);
 
 /*
- * If the feature of optimizing vmemmap pages associated with each HugeTLB
- * page is enabled, the head vmemmap page frame is reused and all of the tail
- * vmemmap addresses map to the head vmemmap page frame (furture details can
- * refer to the figure at the head of the mm/hugetlb_vmemmap.c).  In other
- * words, there are more than one page struct with PG_head associated with each
- * HugeTLB page.  We __know__ that there is only one head page struct, the tail
- * page structs with PG_head are fake head page structs.  We need an approach
- * to distinguish between those two different types of page structs so that
- * compound_head() can return the real head page struct when the parameter is
- * the tail page struct but with PG_head.
- *
- * The page_fixed_fake_head() returns the real head page struct if the @page is
- * fake page head, otherwise, returns @page which can either be a true page
- * head or tail.
+ * Return the real head page struct iff the @page is a fake head page, otherwise
+ * return the @page itself. See Documentation/mm/vmemmap_dedup.rst.
  */
 static __always_inline const struct page *page_fixed_fake_head(const struct page *page)
 {
-	if (!hugetlb_optimize_vmemmap_enabled())
+	if (!static_branch_unlikely(&hugetlb_optimize_vmemmap_key))
 		return page;
 
 	/*
···
 static inline const struct page *page_fixed_fake_head(const struct page *page)
 {
 	return page;
-}
-
-static inline bool hugetlb_optimize_vmemmap_enabled(void)
-{
-	return false;
 }
 #endif
 

include/linux/swapops.h

···
 	atomic_long_dec(&num_poisoned_pages);
 }
 
+static inline void num_poisoned_pages_sub(long i)
+{
+	atomic_long_sub(i, &num_poisoned_pages);
+}
+
 #else
 
 static inline swp_entry_t make_hwpoison_entry(struct page *page)
···
 }
 
 static inline void num_poisoned_pages_inc(void)
+{
+}
+
+static inline void num_poisoned_pages_sub(long i)
 {
 }
 #endif

include/linux/sysctl.h

···
 	return NULL;
 }
 
+static inline void register_sysctl_init(const char *path, struct ctl_table *table)
+{
+}
+
 static inline struct ctl_table_header *register_sysctl_mount_point(const char *path)
 {
 	return NULL;

include/ras/ras_event.h

···
 	EM ( MF_MSG_DIFFERENT_COMPOUND, "different compound page after locking" ) \
 	EM ( MF_MSG_HUGE, "huge page" )					\
 	EM ( MF_MSG_FREE_HUGE, "free huge page" )			\
-	EM ( MF_MSG_NON_PMD_HUGE, "non-pmd-sized huge page" )		\
 	EM ( MF_MSG_UNMAP_FAILED, "unmapping failed page" )		\
 	EM ( MF_MSG_DIRTY_SWAPCACHE, "dirty swapcache page" )		\
 	EM ( MF_MSG_CLEAN_SWAPCACHE, "clean swapcache page" )		\

mm/hugetlb.c

···
 	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		return;
 
-	if (hugetlb_vmemmap_alloc(h, page)) {
+	/*
+	 * If we don't know which subpages are hwpoisoned, we can't free
+	 * the hugepage, so it's leaked intentionally.
+	 */
+	if (HPageRawHwpUnreliable(page))
+		return;
+
+	if (hugetlb_vmemmap_restore(h, page)) {
 		spin_lock_irq(&hugetlb_lock);
 		/*
 		 * If we cannot allocate vmemmap pages, just refuse to free the
···
 		spin_unlock_irq(&hugetlb_lock);
 		return;
 	}
+
+	/*
+	 * Move PageHWPoison flag from head page to the raw error pages,
+	 * which makes any healthy subpages reusable.
+	 */
+	if (unlikely(PageHWPoison(page)))
+		hugetlb_clear_page_hwpoison(page);
 
 	for (i = 0; i < pages_per_huge_page(h);
 	     i++, subpage = mem_map_next(subpage, page, i)) {
···
 
 static inline void flush_free_hpage_work(struct hstate *h)
 {
-	if (hugetlb_optimize_vmemmap_pages(h))
+	if (hugetlb_vmemmap_optimizable(h))
 		flush_work(&free_hpage_work);
 }
 
···
 
 static void __prep_new_huge_page(struct hstate *h, struct page *page)
 {
-	hugetlb_vmemmap_free(h, page);
+	hugetlb_vmemmap_optimize(h, page);
 	INIT_LIST_HEAD(&page->lru);
 	set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
 	hugetlb_set_page_subpool(page, NULL);
···
 		 * Attempt to allocate vmemmmap here so that we can take
 		 * appropriate action on failure.
 		 */
-		rc = hugetlb_vmemmap_alloc(h, head);
+		rc = hugetlb_vmemmap_restore(h, head);
 		if (!rc) {
-			/*
-			 * Move PageHWPoison flag from head page to the raw
-			 * error page, which makes any subpages rather than
-			 * the error page reusable.
-			 */
-			if (PageHWPoison(head) && page != head) {
-				SetPageHWPoison(page);
-				ClearPageHWPoison(head);
-			}
 			update_and_free_page(h, head, false);
 		} else {
 			spin_lock_irq(&hugetlb_lock);
···
 	/* Uncommit the reservation */
 	h->resv_huge_pages -= unused_resv_pages;
 
-	/* Cannot return gigantic pages currently */
-	if (hstate_is_gigantic(h))
+	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		goto out;
 
 	/*
···
 		char buf[32];
 
 		string_get_size(huge_page_size(h), 1, STRING_UNITS_2, buf, 32);
-		pr_info("HugeTLB registered %s page size, pre-allocated %ld pages\n",
+		pr_info("HugeTLB: registered %s page size, pre-allocated %ld pages\n",
 			buf, h->free_huge_pages);
+		pr_info("HugeTLB: %d KiB vmemmap can be freed for a %s page\n",
+			hugetlb_vmemmap_optimizable_size(h) / SZ_1K, buf);
 	}
 }
 
···
 	remove_hugetlb_page_for_demote(h, page, false);
 	spin_unlock_irq(&hugetlb_lock);
 
-	rc = hugetlb_vmemmap_alloc(h, page);
+	rc = hugetlb_vmemmap_restore(h, page);
 	if (rc) {
 		/* Allocation of vmemmmap failed, we can not demote page */
 		spin_lock_irq(&hugetlb_lock);
···
 	h->next_nid_to_free = first_memory_node;
 	snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
 					huge_page_size(h)/1024);
-	hugetlb_vmemmap_init(h);
 
 	parsed_hstate = h;
 }
···
 follow_huge_pud(struct mm_struct *mm, unsigned long address,
 		pud_t *pud, int flags)
 {
-	if (flags & (FOLL_GET | FOLL_PIN))
+	struct page *page = NULL;
+	spinlock_t *ptl;
+	pte_t pte;
+
+	if (WARN_ON_ONCE(flags & FOLL_PIN))
 		return NULL;
 
-	return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
+retry:
+	ptl = huge_pte_lock(hstate_sizelog(PUD_SHIFT), mm, (pte_t *)pud);
+	if (!pud_huge(*pud))
+		goto out;
+	pte = huge_ptep_get((pte_t *)pud);
+	if (pte_present(pte)) {
+		page = pud_page(*pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
+		if (WARN_ON_ONCE(!try_grab_page(page, flags))) {
+			page = NULL;
+			goto out;
+		}
+	} else {
+		if (is_hugetlb_entry_migration(pte)) {
+			spin_unlock(ptl);
+			__migration_entry_wait(mm, (pte_t *)pud, ptl);
+			goto retry;
+		}
+		/*
+		 * hwpoisoned entry is treated as no_page_table in
+		 * follow_page_mask().
+		 */
+	}
+out:
+	spin_unlock(ptl);
+	return page;
 }
 
 struct page * __weak

mm/hugetlb_vmemmap.c

···
 // SPDX-License-Identifier: GPL-2.0
 /*
- * Optimize vmemmap pages associated with HugeTLB
+ * HugeTLB Vmemmap Optimization (HVO)
  *
- * Copyright (c) 2020, Bytedance. All rights reserved.
+ * Copyright (c) 2020, ByteDance. All rights reserved.
  *
  *     Author: Muchun Song <[e-mail]>
  *
···
  */
 #define pr_fmt(fmt)	"HugeTLB: " fmt
 
-#include <linux/memory.h>
+#include <linux/pgtable.h>
+#include <linux/bootmem_info.h>
+#include <asm/pgalloc.h>
+#include <asm/tlbflush.h>
 #include "hugetlb_vmemmap.h"
 
-/*
- * There are a lot of struct page structures associated with each HugeTLB page.
- * For tail pages, the value of compound_head is the same. So we can reuse first
- * page of head page structures. We map the virtual addresses of all the pages
- * of tail page structures to the head page struct, and then free these page
- * frames. Therefore, we need to reserve one pages as vmemmap areas.
+/**
+ * struct vmemmap_remap_walk - walk vmemmap page table
+ *
+ * @remap_pte:		called for each lowest-level entry (PTE).
+ * @nr_walked:		the number of walked pte.
+ * @reuse_page:		the page which is reused for the tail vmemmap pages.
+ * @reuse_addr:		the virtual address of the @reuse_page page.
+ * @vmemmap_pages:	the list head of the vmemmap pages that can be freed
+ *			or is mapped from.
  */
-#define RESERVE_VMEMMAP_NR		1U
-#define RESERVE_VMEMMAP_SIZE		(RESERVE_VMEMMAP_NR << PAGE_SHIFT)
-
-enum vmemmap_optimize_mode {
-	VMEMMAP_OPTIMIZE_OFF,
-	VMEMMAP_OPTIMIZE_ON,
+struct vmemmap_remap_walk {
+	void			(*remap_pte)(pte_t *pte, unsigned long addr,
+					     struct vmemmap_remap_walk *walk);
+	unsigned long		nr_walked;
+	struct page		*reuse_page;
+	unsigned long		reuse_addr;
+	struct list_head	*vmemmap_pages;
 };
 
-DEFINE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
-			hugetlb_optimize_vmemmap_key);
-EXPORT_SYMBOL(hugetlb_optimize_vmemmap_key);
-
-static enum vmemmap_optimize_mode vmemmap_optimize_mode =
-	IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON);
-
-static void vmemmap_optimize_mode_switch(enum vmemmap_optimize_mode to)
+static int __split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
 {
-	if (vmemmap_optimize_mode == to)
-		return;
+	pmd_t __pmd;
+	int i;
+	unsigned long addr = start;
+	struct page *page = pmd_page(*pmd);
+	pte_t *pgtable = pte_alloc_one_kernel(&init_mm);
 
-	if (to == VMEMMAP_OPTIMIZE_OFF)
-		static_branch_dec(&hugetlb_optimize_vmemmap_key);
-	else
-		static_branch_inc(&hugetlb_optimize_vmemmap_key);
-	WRITE_ONCE(vmemmap_optimize_mode, to);
-}
+	if (!pgtable)
+		return -ENOMEM;
 
-static int __init hugetlb_vmemmap_early_param(char *buf)
-{
-	bool enable;
-	enum vmemmap_optimize_mode mode;
+	pmd_populate_kernel(&init_mm, &__pmd, pgtable);
 
-	if (kstrtobool(buf, &enable))
-		return -EINVAL;
+	for (i = 0; i < PTRS_PER_PTE; i++, addr += PAGE_SIZE) {
+		pte_t entry, *pte;
+		pgprot_t pgprot = PAGE_KERNEL;
 
-	mode = enable ? VMEMMAP_OPTIMIZE_ON : VMEMMAP_OPTIMIZE_OFF;
-	vmemmap_optimize_mode_switch(mode);
+		entry = mk_pte(page + i, pgprot);
+		pte = pte_offset_kernel(&__pmd, addr);
+		set_pte_at(&init_mm, addr, pte, entry);
+	}
+
+	spin_lock(&init_mm.page_table_lock);
+	if (likely(pmd_leaf(*pmd))) {
+		/*
+		 * Higher order allocations from buddy allocator must be able to
+		 * be treated as indepdenent small pages (as they can be freed
+		 * individually).
+		 */
+		if (!PageReserved(page))
+			split_page(page, get_order(PMD_SIZE));
+
+		/* Make pte visible before pmd. See comment in pmd_install(). */
+		smp_wmb();
+		pmd_populate_kernel(&init_mm, pmd, pgtable);
+		flush_tlb_kernel_range(start, start + PMD_SIZE);
+	} else {
+		pte_free_kernel(&init_mm, pgtable);
+	}
+	spin_unlock(&init_mm.page_table_lock);
 
 	return 0;
 }
-early_param("hugetlb_free_vmemmap", hugetlb_vmemmap_early_param);
+
+static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
+{
+	int leaf;
+
+	spin_lock(&init_mm.page_table_lock);
+	leaf = pmd_leaf(*pmd);
+	spin_unlock(&init_mm.page_table_lock);
+
+	if (!leaf)
+		return 0;
+
+	return __split_vmemmap_huge_pmd(pmd, start);
+}
+
+static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
+			      unsigned long end,
+			      struct vmemmap_remap_walk *walk)
+{
+	pte_t *pte = pte_offset_kernel(pmd, addr);
+
+	/*
+	 * The reuse_page is found 'first' in table walk before we start
+	 * remapping (which is calling @walk->remap_pte).
+	 */
+	if (!walk->reuse_page) {
+		walk->reuse_page = pte_page(*pte);
+		/*
+		 * Because the reuse address is part of the range that we are
+		 * walking, skip the reuse address range.
+		 */
+		addr += PAGE_SIZE;
+		pte++;
+		walk->nr_walked++;
+	}
+
+	for (; addr != end; addr += PAGE_SIZE, pte++) {
+		walk->remap_pte(pte, addr, walk);
+		walk->nr_walked++;
+	}
+}
+
+static int vmemmap_pmd_range(pud_t *pud, unsigned long addr,
+			     unsigned long end,
+			     struct vmemmap_remap_walk *walk)
+{
+	pmd_t *pmd;
+	unsigned long next;
+
+	pmd = pmd_offset(pud, addr);
+	do {
+		int ret;
+
+		ret = split_vmemmap_huge_pmd(pmd, addr & PMD_MASK);
+		if (ret)
+			return ret;
+
+		next = pmd_addr_end(addr, end);
+		vmemmap_pte_range(pmd, addr, next, walk);
+	} while (pmd++, addr = next, addr != end);
+
+	return 0;
+}
+
+static int vmemmap_pud_range(p4d_t *p4d, unsigned long addr,
+			     unsigned long end,
+			     struct vmemmap_remap_walk *walk)
+{
+	pud_t *pud;
+	unsigned long next;
+
+	pud = pud_offset(p4d, addr);
+	do {
+		int ret;
+
+		next = pud_addr_end(addr, end);
+		ret = vmemmap_pmd_range(pud, addr, next, walk);
+		if (ret)
+			return ret;
+	} while (pud++, addr = next, addr != end);
+
+	return 0;
+}
+
+static int vmemmap_p4d_range(pgd_t *pgd, unsigned long addr,
+			     unsigned long end,
+			     struct vmemmap_remap_walk *walk)
+{
+	p4d_t *p4d;
+	unsigned long next;
+
+	p4d = p4d_offset(pgd, addr);
+	do {
+		int ret;
+
+		next = p4d_addr_end(addr, end);
+		ret = vmemmap_pud_range(p4d, addr, next, walk);
+		if (ret)
+			return ret;
+	} while (p4d++, addr = next, addr != end);
+
+	return 0;
+}
+
+static int vmemmap_remap_range(unsigned long start, unsigned long end,
+			       struct vmemmap_remap_walk *walk)
+{
+	unsigned long addr = start;
+	unsigned long next;
+	pgd_t *pgd;
+
+	VM_BUG_ON(!PAGE_ALIGNED(start));
+	VM_BUG_ON(!PAGE_ALIGNED(end));
+
+	pgd = pgd_offset_k(addr);
+	do {
+		int ret;
+
+		next = pgd_addr_end(addr, end);
+		ret = vmemmap_p4d_range(pgd, addr, next, walk);
+		if (ret)
+			return ret;
+	} while (pgd++, addr = next, addr != end);
+
+	/*
+	 * We only change the mapping of the vmemmap virtual address range
+	 * [@start + PAGE_SIZE, end), so we only need to flush the TLB which
+	 * belongs to the range.
+	 */
+	flush_tlb_kernel_range(start + PAGE_SIZE, end);
+
+	return 0;
+}
 
 /*
- * Previously discarded vmemmap pages will be allocated and remapping
- * after this function returns zero.
+ * Free a vmemmap page. A vmemmap page can be allocated from the memblock
+ * allocator or buddy allocator. If the PG_reserved flag is set, it means
+ * that it allocated from the memblock allocator, just free it via the
+ * free_bootmem_page(). Otherwise, use __free_page().
  */
-int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head)
+static inline void free_vmemmap_page(struct page *page)
+{
+	if (PageReserved(page))
+		free_bootmem_page(page);
+	else
+		__free_page(page);
+}
+
+/* Free a list of the vmemmap pages */
+static void free_vmemmap_page_list(struct list_head *list)
+{
+	struct page *page, *next;
+
+	list_for_each_entry_safe(page, next, list, lru) {
+		list_del(&page->lru);
+		free_vmemmap_page(page);
+	}
+}
+
+static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
+			      struct vmemmap_remap_walk *walk)
+{
+	/*
+	 * Remap the tail pages as read-only to catch illegal write operation
+	 * to the tail pages.
+	 */
+	pgprot_t pgprot = PAGE_KERNEL_RO;
+	pte_t entry = mk_pte(walk->reuse_page, pgprot);
+	struct page *page = pte_page(*pte);
+
+	list_add_tail(&page->lru, walk->vmemmap_pages);
+	set_pte_at(&init_mm, addr, pte, entry);
+}
+
+/*
+ * How many struct page structs need to be reset. When we reuse the head
+ * struct page, the special metadata (e.g. page->flags or page->mapping)
+ * cannot copy to the tail struct page structs. The invalid value will be
+ * checked in the free_tail_pages_check(). In order to avoid the message
+ * of "corrupted mapping in tail page". We need to reset at least 3 (one
+ * head struct page struct and two tail struct page structs) struct page
+ * structs.
+ */
+#define NR_RESET_STRUCT_PAGE		3
+
+static inline void reset_struct_pages(struct page *start)
+{
+	int i;
+	struct page *from = start + NR_RESET_STRUCT_PAGE;
+
+	for (i = 0; i < NR_RESET_STRUCT_PAGE; i++)
+		memcpy(start + i, from, sizeof(*from));
+}
+
+static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
+				struct vmemmap_remap_walk *walk)
+{
+	pgprot_t pgprot = PAGE_KERNEL;
+	struct page *page;
+	void *to;
+
+	BUG_ON(pte_page(*pte) != walk->reuse_page);
+
+	page = list_first_entry(walk->vmemmap_pages, struct page, lru);
+	list_del(&page->lru);
+	to = page_to_virt(page);
+	copy_page(to, (void *)walk->reuse_addr);
+	reset_struct_pages(to);
+
+	set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
+}
+
+/**
+ * vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
+ *			to the page which @reuse is mapped to, then free vmemmap
+ *			which the range are mapped to.
+ * @start:	start address of the vmemmap virtual address range that we want
+ *		to remap.
+ * @end:	end address of the vmemmap virtual address range that we want to
+ *		remap.
+ * @reuse:	reuse address.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+static int vmemmap_remap_free(unsigned long start, unsigned long end,
+			      unsigned long reuse)
 {
 	int ret;
-	unsigned long vmemmap_addr = (unsigned long)head;
-	unsigned long vmemmap_end, vmemmap_reuse, vmemmap_pages;
+	LIST_HEAD(vmemmap_pages);
+	struct vmemmap_remap_walk walk = {
+		.remap_pte	= vmemmap_remap_pte,
+		.reuse_addr	= reuse,
+		.vmemmap_pages	= &vmemmap_pages,
+	};
+
+	/*
+	 * In order to make remapping routine most efficient for the huge pages,
+	 * the routine of vmemmap page table walking has the following rules
+	 * (see more details from the vmemmap_pte_range()):
+	 *
+	 * - The range [@start, @end) and the range [@reuse, @reuse + PAGE_SIZE)
+	 *   should be continuous.
+	 * - The @reuse address is part of the range [@reuse, @end) that we are
+	 *   walking which is passed to vmemmap_remap_range().
+	 * - The @reuse address is the first in the complete range.
+	 *
+	 * So we need to make sure that @start and @reuse meet the above rules.
+	 */
+	BUG_ON(start - reuse != PAGE_SIZE);
+
+	mmap_read_lock(&init_mm);
+	ret = vmemmap_remap_range(reuse, end, &walk);
+	if (ret && walk.nr_walked) {
+		end = reuse + walk.nr_walked * PAGE_SIZE;
+		/*
+		 * vmemmap_pages contains pages from the previous
+		 * vmemmap_remap_range call which failed.  These
+		 * are pages which were removed from the vmemmap.
+		 * They will be restored in the following call.
+		 */
+		walk = (struct vmemmap_remap_walk) {
+			.remap_pte	= vmemmap_restore_pte,
+			.reuse_addr	= reuse,
+			.vmemmap_pages	= &vmemmap_pages,
+		};
+
+		vmemmap_remap_range(reuse, end, &walk);
+	}
+	mmap_read_unlock(&init_mm);
+
+	free_vmemmap_page_list(&vmemmap_pages);
+
+	return ret;
+}
+
+static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
+				   gfp_t gfp_mask, struct list_head *list)
+{
+	unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
+	int nid = page_to_nid((struct page *)start);
+	struct page *page, *next;
+
+	while (nr_pages--) {
+		page = alloc_pages_node(nid, gfp_mask, 0);
+		if (!page)
+			goto out;
+		list_add_tail(&page->lru, list);
+	}
+
+	return 0;
+out:
+	list_for_each_entry_safe(page, next, list, lru)
+		__free_pages(page, 0);
+	return -ENOMEM;
+}
+
+/**
+ * vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
+ *			 to the page which is from the @vmemmap_pages
+ *			 respectively.
+ * @start:	start address of the vmemmap virtual address range that we want
+ *		to remap.
+ * @end:	end address of the vmemmap virtual address range that we want to
+ *		remap.
+ * @reuse:	reuse address.
+ * @gfp_mask:	GFP flag for allocating vmemmap pages.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+static int vmemmap_remap_alloc(unsigned long start, unsigned long end,
+			       unsigned long reuse, gfp_t gfp_mask)
+{
+	LIST_HEAD(vmemmap_pages);
+	struct vmemmap_remap_walk walk = {
+		.remap_pte	= vmemmap_restore_pte,
+		.reuse_addr	= reuse,
+		.vmemmap_pages	= &vmemmap_pages,
+	};
+
+	/* See the comment in the vmemmap_remap_free(). */
+	BUG_ON(start - reuse != PAGE_SIZE);
+
+	if (alloc_vmemmap_page_list(start, end, gfp_mask, &vmemmap_pages))
+		return -ENOMEM;
+
+	mmap_read_lock(&init_mm);
+	vmemmap_remap_range(reuse, end, &walk);
+	mmap_read_unlock(&init_mm);
+
+	return 0;
+}
+
+DEFINE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key);
+EXPORT_SYMBOL(hugetlb_optimize_vmemmap_key);
+
+static bool vmemmap_optimize_enabled = IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON);
+core_param(hugetlb_free_vmemmap, vmemmap_optimize_enabled, bool, 0);
+
+/**
+ * hugetlb_vmemmap_restore - restore previously optimized (by
+ *			     hugetlb_vmemmap_optimize()) vmemmap pages which
+ *			     will be reallocated and remapped.
+ * @h:		struct hstate.
+ * @head:	the head page whose vmemmap pages will be restored.
+ *
+ * Return: %0 if @head's vmemmap pages have been reallocated and remapped,
+ * negative error code otherwise.
+ */
+int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
+{
+	int ret;
+	unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
+	unsigned long vmemmap_reuse;
 
 	if (!HPageVmemmapOptimized(head))
 		return 0;
 
-	vmemmap_addr	+= RESERVE_VMEMMAP_SIZE;
-	vmemmap_pages	= hugetlb_optimize_vmemmap_pages(h);
-	vmemmap_end	= vmemmap_addr + (vmemmap_pages << PAGE_SHIFT);
-	vmemmap_reuse	= vmemmap_addr - PAGE_SIZE;
+	vmemmap_end	= vmemmap_start + hugetlb_vmemmap_size(h);
+	vmemmap_reuse	= vmemmap_start;
+	vmemmap_start	+= HUGETLB_VMEMMAP_RESERVE_SIZE;
 
 	/*
-	 * The pages which the vmemmap virtual address range [@vmemmap_addr,
+	 * The pages which the vmemmap virtual address range [@vmemmap_start,
 	 * @vmemmap_end) are mapped to are freed to the buddy allocator, and
 	 * the range is mapped to the page which @vmemmap_reuse is mapped to.
 	 * When a HugeTLB page is freed to the buddy allocator, previously
 	 * discarded vmemmap pages must be allocated and remapping.
 	 */
-	ret = vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse,
+	ret = vmemmap_remap_alloc(vmemmap_start, vmemmap_end, vmemmap_reuse,
 				  GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE);
 	if (!ret) {
 		ClearHPageVmemmapOptimized(head);
···
 	return ret;
 }
 
-static unsigned int vmemmap_optimizable_pages(struct hstate *h,
-					      struct page *head)
+/* Return true iff a HugeTLB whose vmemmap should and can be optimized. */
+static bool vmemmap_should_optimize(const struct hstate *h, const struct page *head)
 {
-	if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
-		return 0;
+	if (!READ_ONCE(vmemmap_optimize_enabled))
+		return false;
+
+	if (!hugetlb_vmemmap_optimizable(h))
+		return false;
 
 	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
 		pmd_t *pmdp, pmd;
···
 		 *          +-------------------------------------------+
 		 */
 		if (PageVmemmapSelfHosted(vmemmap_page))
-			return 0;
+			return false;
 	}
 
-	return hugetlb_optimize_vmemmap_pages(h);
+	return true;
 }
 
-void hugetlb_vmemmap_free(struct hstate *h, struct page *head)
+/**
+ * hugetlb_vmemmap_optimize - optimize @head page's vmemmap pages.
+ * @h:		struct hstate.
+ * @head:	the head page whose vmemmap pages will be optimized.
+ *
+ * This function only tries to optimize @head's vmemmap pages and does not
+ * guarantee that the optimization will succeed after it returns. The caller
+ * can use HPageVmemmapOptimized(@head) to detect if @head's vmemmap pages
+ * have been optimized.
+ */
+void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
 {
-	unsigned long vmemmap_addr = (unsigned long)head;
-	unsigned long vmemmap_end, vmemmap_reuse, vmemmap_pages;
+	unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
+	unsigned long vmemmap_reuse;
 
-	vmemmap_pages = vmemmap_optimizable_pages(h, head);
-	if (!vmemmap_pages)
+	if (!vmemmap_should_optimize(h, head))
 		return;
 
 	static_branch_inc(&hugetlb_optimize_vmemmap_key);
 
-	vmemmap_addr	+= RESERVE_VMEMMAP_SIZE;
-	vmemmap_end	= vmemmap_addr + (vmemmap_pages << PAGE_SHIFT);
-	vmemmap_reuse	= vmemmap_addr - PAGE_SIZE;
+	vmemmap_end	= vmemmap_start + hugetlb_vmemmap_size(h);
+	vmemmap_reuse	= vmemmap_start;
+	vmemmap_start	+= HUGETLB_VMEMMAP_RESERVE_SIZE;
 
 	/*
-	 * Remap the vmemmap virtual address range [@vmemmap_addr, @vmemmap_end)
+	 * Remap the vmemmap virtual address range [@vmemmap_start, @vmemmap_end)
 	 * to the page which @vmemmap_reuse is mapped to, then free the pages
-	 * which the range [@vmemmap_addr, @vmemmap_end] is mapped to.
+	 * which the range [@vmemmap_start, @vmemmap_end] is mapped to.
 	 */
-	if (vmemmap_remap_free(vmemmap_addr, vmemmap_end, vmemmap_reuse))
+	if (vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse))
 		static_branch_dec(&hugetlb_optimize_vmemmap_key);
 	else
 		SetHPageVmemmapOptimized(head);
 }
 
-void __init hugetlb_vmemmap_init(struct hstate *h)
-{
-	unsigned int nr_pages = pages_per_huge_page(h);
-	unsigned int vmemmap_pages;
-
-	/*
-	 * There are only (RESERVE_VMEMMAP_SIZE / sizeof(struct page)) struct
-	 * page structs that can be used when CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP,
-	 * so add a BUILD_BUG_ON to catch invalid usage of the tail struct page.
-	 */
-	BUILD_BUG_ON(__NR_USED_SUBPAGE >=
-		     RESERVE_VMEMMAP_SIZE / sizeof(struct page));
-
-	if (!is_power_of_2(sizeof(struct page))) {
-		pr_warn_once("cannot optimize vmemmap pages because \"struct page\" crosses page boundaries\n");
-		static_branch_disable(&hugetlb_optimize_vmemmap_key);
-		return;
-	}
-
-	vmemmap_pages = (nr_pages * sizeof(struct page)) >> PAGE_SHIFT;
-	/*
-	 * The head page is not to be freed to buddy allocator, the other tail
-	 * pages will map to the head page, so they can be freed.
-	 *
-	 * Could RESERVE_VMEMMAP_NR be greater than @vmemmap_pages? It is true
-	 * on some architectures (e.g. aarch64). See Documentation/arm64/
-	 * hugetlbpage.rst for more details.
-	 */
-	if (likely(vmemmap_pages > RESERVE_VMEMMAP_NR))
-		h->optimize_vmemmap_pages = vmemmap_pages - RESERVE_VMEMMAP_NR;
-
-	pr_info("can optimize %d vmemmap pages for %s\n",
-		h->optimize_vmemmap_pages, h->name);
-}
-
-#ifdef CONFIG_PROC_SYSCTL
-static int hugetlb_optimize_vmemmap_handler(struct ctl_table *table, int write,
-					    void *buffer, size_t *length,
-					    loff_t *ppos)
-{
-	int ret;
-	enum vmemmap_optimize_mode mode;
-	static DEFINE_MUTEX(sysctl_mutex);
-
-	if (write && !capable(CAP_SYS_ADMIN))
-		return -EPERM;
-
-	mutex_lock(&sysctl_mutex);
-	mode = vmemmap_optimize_mode;
-	table->data = &mode;
-	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
-	if (write && !ret)
-		vmemmap_optimize_mode_switch(mode);
-	mutex_unlock(&sysctl_mutex);
-
-	return ret;
-}
-
 static struct ctl_table hugetlb_vmemmap_sysctls[] = {
 	{
 		.procname	= "hugetlb_optimize_vmemmap",
-		.maxlen		= sizeof(enum vmemmap_optimize_mode),
+		.data		= &vmemmap_optimize_enabled,
+		.maxlen		= sizeof(int),
 		.mode		= 0644,
-		.proc_handler	= hugetlb_optimize_vmemmap_handler,
-		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_ONE,
+		.proc_handler	= proc_dobool,
 	},
 	{ }
 };
 
-static __init int hugetlb_vmemmap_sysctls_init(void)
+static int __init hugetlb_vmemmap_init(void)
 {
-	/*
-	 * If "struct page" crosses page boundaries, the vmemmap pages cannot
-	 * be optimized.
-	 */
-	if (is_power_of_2(sizeof(struct page)))
-		register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
+	/* HUGETLB_VMEMMAP_RESERVE_SIZE should cover all used struct pages */
+	BUILD_BUG_ON(__NR_USED_SUBPAGE * sizeof(struct page) > HUGETLB_VMEMMAP_RESERVE_SIZE);
 
+	if (IS_ENABLED(CONFIG_PROC_SYSCTL)) {
+		const struct hstate *h;
+
+		for_each_hstate(h) {
+			if (hugetlb_vmemmap_optimizable(h)) {
+				register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
+				break;
+			}
+		}
+	}
 	return 0;
 }
-late_initcall(hugetlb_vmemmap_sysctls_init);
-#endif /* CONFIG_PROC_SYSCTL */
+late_initcall(hugetlb_vmemmap_init);

mm/hugetlb_vmemmap.h

···
 // SPDX-License-Identifier: GPL-2.0
 /*
- * Optimize vmemmap pages associated with HugeTLB
+ * HugeTLB Vmemmap Optimization (HVO)
  *
- * Copyright (c) 2020, Bytedance. All rights reserved.
+ * Copyright (c) 2020, ByteDance. All rights reserved.
  *
  *     Author: Muchun Song <[e-mail]>
  */
···
 #include <linux/hugetlb.h>
 
 #ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
-int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head);
-void hugetlb_vmemmap_free(struct hstate *h, struct page *head);
-void hugetlb_vmemmap_init(struct hstate *h);
+int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head);
+void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head);
 
 /*
- * How many vmemmap pages associated with a HugeTLB page that can be
- * optimized and freed to the buddy allocator.
+ * Reserve one vmemmap page, all vmemmap addresses are mapped to it. See
+ * Documentation/vm/vmemmap_dedup.rst.
  */
-static inline unsigned int hugetlb_optimize_vmemmap_pages(struct hstate *h)
+#define HUGETLB_VMEMMAP_RESERVE_SIZE	PAGE_SIZE
+
+static inline unsigned int hugetlb_vmemmap_size(const struct hstate *h)
 {
-	return h->optimize_vmemmap_pages;
+	return pages_per_huge_page(h) * sizeof(struct page);
+}
+
+/*
+ * Return how many vmemmap size associated with a HugeTLB page that can be
+ * optimized and can be freed to the buddy allocator.
+ */
+static inline unsigned int hugetlb_vmemmap_optimizable_size(const struct hstate *h)
+{
+	int size = hugetlb_vmemmap_size(h) - HUGETLB_VMEMMAP_RESERVE_SIZE;
+
+	if (!is_power_of_2(sizeof(struct page)))
+		return 0;
+	return size > 0 ? size : 0;
 }
 #else
-static inline int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head)
+static inline int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
 {
 	return 0;
 }
 
-static inline void hugetlb_vmemmap_free(struct hstate *h, struct page *head)
+static inline void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
 {
 }
 
-static inline void hugetlb_vmemmap_init(struct hstate *h)
-{
-}
-
-static inline unsigned int hugetlb_optimize_vmemmap_pages(struct hstate *h)
+static inline unsigned int hugetlb_vmemmap_optimizable_size(const struct hstate *h)
 {
 	return 0;
 }
 #endif /* CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP */
+
+static inline bool hugetlb_vmemmap_optimizable(const struct hstate *h)
+{
+	return hugetlb_vmemmap_optimizable_size(h) != 0;
+}
 #endif /* _LINUX_HUGETLB_VMEMMAP_H */

mm/memory-failure.c

···
 
 static bool hw_memory_failure __read_mostly = false;
 
-static bool __page_handle_poison(struct page *page)
+/*
+ * Return values:
+ *   1:   the page is dissolved (if needed) and taken off from buddy,
+ *   0:   the page is dissolved (if needed) and not taken off from buddy,
+ *   < 0: failed to dissolve.
+ */
+static int __page_handle_poison(struct page *page)
 {
 	int ret;
 
···
 		ret = take_page_off_buddy(page);
 	zone_pcp_enable(page_zone(page));
 
-	return ret > 0;
+	return ret;
 }
 
 static bool page_handle_poison(struct page *page, bool hugepage_or_freepage, bool release)
···
 		 * Doing this check for free pages is also fine since dissolve_free_huge_page
 		 * returns 0 for non-hugetlb pages as well.
 		 */
-		if (!__page_handle_poison(page))
+		if (__page_handle_poison(page) <= 0)
 			/*
 			 * We could fail to take off the target page from buddy
 			 * for example due to racy page allocation, but that's
···
 	[MF_MSG_DIFFERENT_COMPOUND]	= "different compound page after locking",
 	[MF_MSG_HUGE]			= "huge page",
 	[MF_MSG_FREE_HUGE]		= "free huge page",
-	[MF_MSG_NON_PMD_HUGE]		= "non-pmd-sized huge page",
 	[MF_MSG_UNMAP_FAILED]		= "unmapping failed page",
 	[MF_MSG_DIRTY_SWAPCACHE]	= "dirty swapcache page",
 	[MF_MSG_CLEAN_SWAPCACHE]	= "clean swapcache page",
···
 		res = truncate_error_page(hpage, page_to_pfn(p), mapping);
 		unlock_page(hpage);
 	} else {
-		res = MF_FAILED;
 		unlock_page(hpage);
 		/*
 		 * migration entry prevents later access on error hugepage,
···
 		 * subpages.
 		 */
 		put_page(hpage);
-		if (__page_handle_poison(p)) {
+		if (__page_handle_poison(p) >= 0) {
 			page_ref_inc(p);
 			res = MF_RECOVERED;
+		} else {
+			res = MF_FAILED;
 		}
 	}
 
···
 EXPORT_SYMBOL_GPL(mf_dax_kill_procs);
 #endif /* CONFIG_FS_DAX */
 
+#ifdef CONFIG_HUGETLB_PAGE
+/*
+ * Struct raw_hwp_page represents information about "raw error page",
+ * constructing singly linked list originated from ->private field of
+ * SUBPAGE_INDEX_HWPOISON-th tail page.
+ */
+struct raw_hwp_page {
+	struct llist_node node;
+	struct page *page;
+};
+
+static inline struct llist_head *raw_hwp_list_head(struct page *hpage)
+{
+	return (struct llist_head *)&page_private(hpage + SUBPAGE_INDEX_HWPOISON);
+}
+
+static unsigned long __free_raw_hwp_pages(struct page *hpage, bool move_flag)
+{
+	struct llist_head *head;
+	struct llist_node *t, *tnode;
+	unsigned long count = 0;
+
+	head = raw_hwp_list_head(hpage);
+	llist_for_each_safe(tnode, t, head->first) {
+		struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
+
+		if (move_flag)
+			SetPageHWPoison(p->page);
+		kfree(p);
+		count++;
+	}
+	llist_del_all(head);
+	return count;
+}
+
+static int hugetlb_set_page_hwpoison(struct page *hpage, struct page *page)
+{
+	struct llist_head *head;
+	struct raw_hwp_page *raw_hwp;
+	struct llist_node *t, *tnode;
+	int ret = TestSetPageHWPoison(hpage) ? -EHWPOISON : 0;
+
+	/*
+	 * Once the hwpoison hugepage has lost reliable raw error info,
+	 * there is little meaning to keep additional error info precisely,
+	 * so skip to add additional raw error info.
+	 */
+	if (HPageRawHwpUnreliable(hpage))
+		return -EHWPOISON;
+	head = raw_hwp_list_head(hpage);
+	llist_for_each_safe(tnode, t, head->first) {
+		struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
+
+		if (p->page == page)
+			return -EHWPOISON;
+	}
+
+	raw_hwp = kmalloc(sizeof(struct raw_hwp_page), GFP_ATOMIC);
+	if (raw_hwp) {
+		raw_hwp->page = page;
+		llist_add(&raw_hwp->node, head);
+		/* the first error event will be counted in action_result(). */
+		if (ret)
+			num_poisoned_pages_inc();
+	} else {
+		/*
+		 * Failed to save raw error info.  We no longer trace all
+		 * hwpoisoned subpages, and we need refuse to free/dissolve
+		 * this hwpoisoned hugepage.
+		 */
+		SetHPageRawHwpUnreliable(hpage);
+		/*
+		 * Once HPageRawHwpUnreliable is set, raw_hwp_page is not
+		 * used any more, so free it.
+		 */
+		__free_raw_hwp_pages(hpage, false);
+	}
+	return ret;
+}
+
+static unsigned long free_raw_hwp_pages(struct page *hpage, bool move_flag)
+{
+	/*
+	 * HPageVmemmapOptimized hugepages can't be freed because struct
+	 * pages for tail pages are required but they don't exist.
+	 */
+	if (move_flag && HPageVmemmapOptimized(hpage))
+		return 0;
+
+	/*
+	 * HPageRawHwpUnreliable hugepages shouldn't be unpoisoned by
+	 * definition.
+	 */
+	if (HPageRawHwpUnreliable(hpage))
+		return 0;
+
+	return __free_raw_hwp_pages(hpage, move_flag);
+}
+
+void hugetlb_clear_page_hwpoison(struct page *hpage)
+{
+	if (HPageRawHwpUnreliable(hpage))
+		return;
+	ClearPageHWPoison(hpage);
+	free_raw_hwp_pages(hpage, true);
+}
+
 /*
  * Called from hugetlb code with hugetlb_lock held.
  *
···
 			count_increased = true;
 	} else {
 		ret = -EBUSY;
-		goto out;
+		if (!(flags & MF_NO_RETRY))
+			goto out;
 	}
 
-	if (TestSetPageHWPoison(head)) {
+	if (hugetlb_set_page_hwpoison(head, page)) {
 		ret = -EHWPOISON;
 		goto out;
 	}
···
 	return ret;
 }
 
-#ifdef CONFIG_HUGETLB_PAGE
 /*
  * Taking refcount of hugetlb pages needs extra care about race conditions
  * with basic operations like hugepage allocation/free/demotion.
···
 	struct page *p = pfn_to_page(pfn);
 	struct page *head;
 	unsigned long page_flags;
-	bool retry = true;
 
 	*hugetlb = 1;
 retry:
···
 		}
 		return res;
 	} else if (res == -EBUSY) {
-		if (retry) {
-			retry = false;
+		if (!(flags & MF_NO_RETRY)) {
+			flags |= MF_NO_RETRY;
 			goto retry;
 		}
 		action_result(pfn, MF_MSG_UNKNOWN, MF_IGNORED);
···
 	lock_page(head);
 
 	if (hwpoison_filter(p)) {
-		ClearPageHWPoison(head);
+		hugetlb_clear_page_hwpoison(head);
 		res = -EOPNOTSUPP;
 		goto out;
 	}
···
 	 */
 	if (res == 0) {
 		unlock_page(head);
-		res = MF_FAILED;
-		if (__page_handle_poison(p)) {
+		if (__page_handle_poison(p) >= 0) {
 			page_ref_inc(p);
 			res = MF_RECOVERED;
+		} else {
+			res = MF_FAILED;
 		}
 		action_result(pfn, MF_MSG_FREE_HUGE, res);
 		return res == MF_RECOVERED ? 0 : -EBUSY;
 	}
 
 	page_flags = head->flags;
-
-	/*
-	 * TODO: hwpoison for pud-sized hugetlb doesn't work right now, so
-	 * simply disable it. In order to make it work properly, we need
-	 * make sure that:
-	 *  - conversion of a pud that maps an error hugetlb into hwpoison
-	 *    entry properly works, and
-	 *  - other mm code walking over page table is aware of pud-aligned
-	 *    hwpoison entries.
-	 */
-	if (huge_page_size(page_hstate(head)) > PMD_SIZE) {
-		action_result(pfn, MF_MSG_NON_PMD_HUGE, MF_IGNORED);
-		res = -EBUSY;
-		goto out;
-	}
 
 	if (!hwpoison_user_mappings(p, pfn, flags, head)) {
 		action_result(pfn, MF_MSG_UNMAP_FAILED, MF_IGNORED);
···
 	return 0;
 }
 
+static inline unsigned long free_raw_hwp_pages(struct page *hpage, bool flag)
+{
+	return 0;
+}
 #endif	/* CONFIG_HUGETLB_PAGE */
 
 static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
···
 	struct page *p;
 	int ret = -EBUSY;
 	int freeit = 0;
+	unsigned long count = 1;
 	static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
 					DEFAULT_RATELIMIT_BURST);
 
···
 
 	ret = get_hwpoison_page(p, MF_UNPOISON);
 	if (!ret) {
+		if (PageHuge(p)) {
+			count = free_raw_hwp_pages(page, false);
+			if (count == 0) {
+				ret = -EBUSY;
+				goto unlock_mutex;
+			}
+		}
 		ret = TestClearPageHWPoison(page) ? 0 : -EBUSY;
 	} else if (ret < 0) {
 		if (ret == -EHWPOISON) {
···
 			unpoison_pr_info("Unpoison: failed to grab page %#lx\n",
 					 pfn, &unpoison_rs);
 	} else {
+		if (PageHuge(p)) {
+			count = free_raw_hwp_pages(page, false);
+			if (count == 0) {
+				ret = -EBUSY;
+				goto unlock_mutex;
+			}
+		}
 		freeit = !!TestClearPageHWPoison(p);
 
 		put_page(page);
···
 unlock_mutex:
 	mutex_unlock(&mf_mutex);
 	if (!ret || freeit) {
-		num_poisoned_pages_dec();
+		num_poisoned_pages_sub(count);
 		unpoison_pr_info("Unpoison: Software-unpoisoned page %#lx\n",
 				 page_to_pfn(p), &unpoison_rs);
 	}

mm/sparse-vmemmap.c

···
 #include <linux/spinlock.h>
 #include <linux/vmalloc.h>
 #include <linux/sched.h>
-#include <linux/pgtable.h>
-#include <linux/bootmem_info.h>
 
 #include <asm/dma.h>
 #include <asm/pgalloc.h>
-#include <asm/tlbflush.h>
-
-#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
-/**
- * struct vmemmap_remap_walk - walk vmemmap page table
- *
- * @remap_pte:		called for each lowest-level entry (PTE).
- * @nr_walked:		the number of walked pte.
- * @reuse_page:		the page which is reused for the tail vmemmap pages.
- * @reuse_addr:		the virtual address of the @reuse_page page.
- * @vmemmap_pages:	the list head of the vmemmap pages that can be freed
- *			or is mapped from.
- */
-struct vmemmap_remap_walk {
-	void (*remap_pte)(pte_t *pte, unsigned long addr,
-			  struct vmemmap_remap_walk *walk);
-	unsigned long nr_walked;
-	struct page *reuse_page;
-	unsigned long reuse_addr;
-	struct list_head *vmemmap_pages;
-};
-
-static int __split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
-{
-	pmd_t __pmd;
-	int i;
-	unsigned long addr = start;
-	struct page *page = pmd_page(*pmd);
-	pte_t *pgtable = pte_alloc_one_kernel(&init_mm);
-
-	if (!pgtable)
-		return -ENOMEM;
-
-	pmd_populate_kernel(&init_mm, &__pmd, pgtable);
-
-	for (i = 0; i < PMD_SIZE / PAGE_SIZE; i++, addr += PAGE_SIZE) {
-		pte_t entry, *pte;
-		pgprot_t pgprot = PAGE_KERNEL;
-
-		entry = mk_pte(page + i, pgprot);
-		pte = pte_offset_kernel(&__pmd, addr);
-		set_pte_at(&init_mm, addr, pte, entry);
-	}
-
-	spin_lock(&init_mm.page_table_lock);
-	if (likely(pmd_leaf(*pmd))) {
-		/*
-		 * Higher order allocations from buddy allocator must be able to
-		 * be treated as indepdenent small pages (as they can be freed
-		 * individually).
-		 */
-		if (!PageReserved(page))
-			split_page(page, get_order(PMD_SIZE));
-
-		/* Make pte visible before pmd. See comment in pmd_install(). */
-		smp_wmb();
-		pmd_populate_kernel(&init_mm, pmd, pgtable);
-		flush_tlb_kernel_range(start, start + PMD_SIZE);
-	} else {
-		pte_free_kernel(&init_mm, pgtable);
-	}
-	spin_unlock(&init_mm.page_table_lock);
-
-	return 0;
-}
-
-static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
-{
-	int leaf;
-
-	spin_lock(&init_mm.page_table_lock);
-	leaf = pmd_leaf(*pmd);
-	spin_unlock(&init_mm.page_table_lock);
-
-	if (!leaf)
-		return 0;
-
-	return __split_vmemmap_huge_pmd(pmd, start);
-}
-
-static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
-			      unsigned long end,
-			      struct vmemmap_remap_walk *walk)
-{
-	pte_t *pte = pte_offset_kernel(pmd, addr);
-
-	/*
-	 * The reuse_page is found 'first' in table walk before we start
-	 * remapping (which is calling @walk->remap_pte).
-	 */
-	if (!walk->reuse_page) {
-		walk->reuse_page = pte_page(*pte);
-		/*
-		 * Because the reuse address is part of the range that we are
-		 * walking, skip the reuse address range.
-		 */
-		addr += PAGE_SIZE;
-		pte++;
-		walk->nr_walked++;
-	}
-
-	for (; addr != end; addr += PAGE_SIZE, pte++) {
-		walk->remap_pte(pte, addr, walk);
-		walk->nr_walked++;
-	}
-}
-
-static int vmemmap_pmd_range(pud_t *pud, unsigned long addr,
-			     unsigned long end,
-			     struct vmemmap_remap_walk *walk)
-{
-	pmd_t *pmd;
-	unsigned long next;
-
-	pmd = pmd_offset(pud, addr);
-	do {
-		int ret;
-
-		ret = split_vmemmap_huge_pmd(pmd, addr & PMD_MASK);
-		if (ret)
-			return ret;
-
-		next = pmd_addr_end(addr, end);
-		vmemmap_pte_range(pmd, addr, next, walk);
-	} while (pmd++, addr = next, addr != end);
-
-	return 0;
-}
-
-static int vmemmap_pud_range(p4d_t *p4d, unsigned long addr,
-			     unsigned long end,
-			     struct vmemmap_remap_walk *walk)
-{
-	pud_t *pud;
-	unsigned long next;
-
-	pud = pud_offset(p4d, addr);
-	do {
-		int ret;
-
-		next = pud_addr_end(addr, end);
-		ret = vmemmap_pmd_range(pud, addr, next, walk);
-		if (ret)
-			return ret;
-	} while (pud++, addr = next, addr != end);
-
-	return 0;
-}
-
-static int vmemmap_p4d_range(pgd_t *pgd, unsigned long addr,
-			     unsigned long end,
-			     struct vmemmap_remap_walk *walk)
-{
-	p4d_t *p4d;
-	unsigned long next;
-
-	p4d = p4d_offset(pgd, addr);
-	do {
-		int ret;
-
-		next = p4d_addr_end(addr, end);
-		ret = vmemmap_pud_range(p4d, addr, next, walk);
-		if (ret)
-			return ret;
-	} while (p4d++, addr = next, addr != end);
-
-	return 0;
-}
-
-static int vmemmap_remap_range(unsigned long start, unsigned long end,
-			       struct vmemmap_remap_walk *walk)
-{
-	unsigned long addr = start;
-	unsigned long next;
-	pgd_t *pgd;
-
-	VM_BUG_ON(!PAGE_ALIGNED(start));
-	VM_BUG_ON(!PAGE_ALIGNED(end));
-
-	pgd = pgd_offset_k(addr);
-	do {
-		int ret;
-
-		next = pgd_addr_end(addr, end);
-		ret = vmemmap_p4d_range(pgd, addr, next, walk);
-		if (ret)
-			return ret;
-	} while (pgd++, addr = next, addr != end);
-
-	/*
-	 * We only change the mapping of the vmemmap virtual address range
-	 * [@start + PAGE_SIZE, end), so we only need to flush the TLB which
-	 * belongs to the range.
-	 */
-	flush_tlb_kernel_range(start + PAGE_SIZE, end);
-
-	return 0;
-}
-
-/*
- * Free a vmemmap page. A vmemmap page can be allocated from the memblock
- * allocator or buddy allocator. If the PG_reserved flag is set, it means
- * that it allocated from the memblock allocator, just free it via the
- * free_bootmem_page(). Otherwise, use __free_page().
- */
-static inline void free_vmemmap_page(struct page *page)
-{
-	if (PageReserved(page))
-		free_bootmem_page(page);
-	else
-		__free_page(page);
-}
-
-/* Free a list of the vmemmap pages */
-static void free_vmemmap_page_list(struct list_head *list)
-{
-	struct page *page, *next;
-
-	list_for_each_entry_safe(page, next, list, lru) {
-		list_del(&page->lru);
-		free_vmemmap_page(page);
-	}
-}
-
-static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
-			      struct vmemmap_remap_walk *walk)
-{
-	/*
-	 * Remap the tail pages as read-only to catch illegal write operation
-	 * to the tail pages.
-	 */
-	pgprot_t pgprot = PAGE_KERNEL_RO;
-	pte_t entry = mk_pte(walk->reuse_page, pgprot);
-	struct page *page = pte_page(*pte);
-
-	list_add_tail(&page->lru, walk->vmemmap_pages);
-	set_pte_at(&init_mm, addr, pte, entry);
-}
-
-/*
- * How many struct page structs need to be reset. When we reuse the head
- * struct page, the special metadata (e.g. page->flags or page->mapping)
- * cannot copy to the tail struct page structs. The invalid value will be
- * checked in the free_tail_pages_check(). In order to avoid the message
- * of "corrupted mapping in tail page". We need to reset at least 3 (one
- * head struct page struct and two tail struct page structs) struct page
- * structs.
- */
-#define NR_RESET_STRUCT_PAGE		3
-
-static inline void reset_struct_pages(struct page *start)
-{
-	int i;
-	struct page *from = start + NR_RESET_STRUCT_PAGE;
-
-	for (i = 0; i < NR_RESET_STRUCT_PAGE; i++)
-		memcpy(start + i, from, sizeof(*from));
-}
-
-static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
-				struct vmemmap_remap_walk *walk)
-{
-	pgprot_t pgprot = PAGE_KERNEL;
-	struct page *page;
-	void *to;
-
-	BUG_ON(pte_page(*pte) != walk->reuse_page);
-
-	page = list_first_entry(walk->vmemmap_pages, struct page, lru);
-	list_del(&page->lru);
-	to = page_to_virt(page);
-	copy_page(to, (void *)walk->reuse_addr);
-	reset_struct_pages(to);
-
-	set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
-}
-
-/**
- * vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
- *			to the page which @reuse is mapped to, then free vmemmap
- *			which the range are mapped to.
- * @start:	start address of the vmemmap virtual address range that we want
- *		to remap.
- * @end:	end address of the vmemmap virtual address range that we want to
- *		remap.
- * @reuse:	reuse address.
- *
- * Return: %0 on success, negative error code otherwise.
- */
-int vmemmap_remap_free(unsigned long start, unsigned long end,
-		       unsigned long reuse)
-{
-	int ret;
-	LIST_HEAD(vmemmap_pages);
-	struct vmemmap_remap_walk walk = {
-		.remap_pte	= vmemmap_remap_pte,
-		.reuse_addr	= reuse,
-		.vmemmap_pages	= &vmemmap_pages,
-	};
-
-	/*
-	 * In order to make remapping routine most efficient for the huge pages,
-	 * the routine of vmemmap page table walking has the following rules
-	 * (see more details from the vmemmap_pte_range()):
-	 *
-	 * - The range [@start, @end) and the range [@reuse, @reuse + PAGE_SIZE)
-	 *   should be continuous.
-	 * - The @reuse address is part of the range [@reuse, @end) that we are
-	 *   walking which is passed to vmemmap_remap_range().
-	 * - The @reuse address is the first in the complete range.
-	 *
-	 * So we need to make sure that @start and @reuse meet the above rules.
-	 */
-	BUG_ON(start - reuse != PAGE_SIZE);
-
-	mmap_read_lock(&init_mm);
-	ret = vmemmap_remap_range(reuse, end, &walk);
-	if (ret && walk.nr_walked) {
-		end = reuse + walk.nr_walked * PAGE_SIZE;
-		/*
-		 * vmemmap_pages contains pages from the previous
-		 * vmemmap_remap_range call which failed.  These
-		 * are pages which were removed from the vmemmap.
-		 * They will be restored in the following call.
-		 */
-		walk = (struct vmemmap_remap_walk) {
-			.remap_pte	= vmemmap_restore_pte,
-			.reuse_addr	= reuse,
-			.vmemmap_pages	= &vmemmap_pages,
-		};
-
-		vmemmap_remap_range(reuse, end, &walk);
-	}
-	mmap_read_unlock(&init_mm);
-
-	free_vmemmap_page_list(&vmemmap_pages);
-
-	return ret;
-}
-
-static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
-				   gfp_t gfp_mask, struct list_head *list)
-{
-	unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
-	int nid = page_to_nid((struct page *)start);
-	struct page *page, *next;
-
-	while (nr_pages--) {
-		page = alloc_pages_node(nid, gfp_mask, 0);
-		if (!page)
-			goto out;
-		list_add_tail(&page->lru, list);
-	}
-
-	return 0;
-out:
-	list_for_each_entry_safe(page, next, list, lru)
-		__free_pages(page, 0);
-	return -ENOMEM;
-}
-
-/**
- * vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
- *			 to the page which is from the @vmemmap_pages
- *			 respectively.
- * @start:	start address of the vmemmap virtual address range that we want
- *		to remap.
- * @end:	end address of the vmemmap virtual address range that we want to
- *		remap.
- * @reuse:	reuse address.
- * @gfp_mask:	GFP flag for allocating vmemmap pages.
- *
- * Return: %0 on success, negative error code otherwise.
- */
-int vmemmap_remap_alloc(unsigned long start, unsigned long end,
-			unsigned long reuse, gfp_t gfp_mask)
-{
-	LIST_HEAD(vmemmap_pages);
-	struct vmemmap_remap_walk walk = {
-		.remap_pte	= vmemmap_restore_pte,
-		.reuse_addr	= reuse,
-		.vmemmap_pages	= &vmemmap_pages,
-	};
-
-	/* See the comment in the vmemmap_remap_free(). */
-	BUG_ON(start - reuse != PAGE_SIZE);
-
-	if (alloc_vmemmap_page_list(start, end, gfp_mask, &vmemmap_pages))
-		return -ENOMEM;
-
-	mmap_read_lock(&init_mm);
-	vmemmap_remap_range(reuse, end, &walk);
-	mmap_read_unlock(&init_mm);
-
-	return 0;
-}
-#endif /* CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP */
 
 /*
  * Allocate a block of memory to be used to back the virtual memory map