diff --git a/include/linux/bootmem_info.h b/include/linux/bootmem_info.h
index 4ed6dee1adc9e395e68a1ea66a46b2806e94b089..2bc8b1f69c93cbff94520d98a3e15302bc87f367 100644
--- a/include/linux/bootmem_info.h
+++ b/include/linux/bootmem_info.h
@@ -2,7 +2,7 @@
#ifndef __LINUX_BOOTMEM_INFO_H
#define __LINUX_BOOTMEM_INFO_H
-#include <linux/mmzone.h>
+#include <linux/mm.h>
/*
* Types for free bootmem stored in page->lru.next. These have to be in
@@ -22,6 +22,27 @@ void __init register_page_bootmem_info_node(struct pglist_data *pgdat);
void get_page_bootmem(unsigned long info, struct page *page,
unsigned long type);
void put_page_bootmem(struct page *page);
+
+/*
+ * Any memory allocated via the memblock allocator and not via the
+ * buddy will be marked reserved already in the memmap. For those
+ * pages, we can call this function to free it to buddy allocator.
+ */
+static inline void free_bootmem_page(struct page *page)
+{
+ unsigned long magic = (unsigned long)page->freelist;
+
+ /*
+ * The reserve_bootmem_region sets the reserved flag on bootmem
+ * pages.
+ */
+ VM_BUG_ON_PAGE(page_ref_count(page) != 2, page);
+
+ if (magic == SECTION_INFO || magic == MIX_SECTION_INFO)
+ put_page_bootmem(page);
+ else
+ VM_BUG_ON_PAGE(1, page);
+}
#else
static inline void register_page_bootmem_info_node(struct pglist_data *pgdat)
{
@@ -35,6 +56,11 @@ static inline void get_page_bootmem(unsigned long info, struct page *page,
unsigned long type)
{
}
+
+static inline void free_bootmem_page(struct page *page)
+{
+ free_reserved_page(page);
+}
#endif
#endif /* __LINUX_BOOTMEM_INFO_H */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 07922ee1477ec6f93b09b6c61fce3318f408d004..3437aa7c6c9105d8f550ff9e570caadc771233b5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3076,6 +3076,9 @@ static inline void print_vma_addr(char *prefix, unsigned long rip)
}
#endif
+void vmemmap_remap_free(unsigned long start, unsigned long end,
+ unsigned long reuse);
+
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);
diff --git a/mm/Makefile b/mm/Makefile
index 61ce71ddf7bb06337515c1e34f1c66ea016ed93e..74b47c354682e06c9d9bfc074f93a93cd1a8f57e 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -75,6 +75,7 @@ obj-$(CONFIG_FRONTSWAP) += frontswap.o
obj-$(CONFIG_ZSWAP) += zswap.o
obj-$(CONFIG_HAS_DMA) += dmapool.o
obj-$(CONFIG_HUGETLBFS) += hugetlb.o
+obj-$(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP) += hugetlb_vmemmap.o
obj-$(CONFIG_NUMA) += mempolicy.o
obj-$(CONFIG_SPARSEMEM) += sparse.o
obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 103f1187043f8f4b8a83e4e37c82e92d29527314..5f5493f0f00336a93a28cc58278dec346ac701d8 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -41,6 +41,7 @@
#include <linux/node.h>
#include <linux/page_owner.h>
#include "internal.h"
+#include "hugetlb_vmemmap.h"
int hugetlb_max_hstate __read_mostly;
unsigned int default_hstate_idx;
@@ -1493,8 +1494,9 @@ static void __prep_account_new_huge_page(struct hstate *h, int nid)
h->nr_huge_pages_node[nid]++;
}
-static void __prep_new_huge_page(struct page *page)
+static void __prep_new_huge_page(struct hstate *h, struct page *page)
{
+ free_huge_page_vmemmap(h, page);
INIT_LIST_HEAD(&page->lru);
set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
hugetlb_set_page_subpool(page, NULL);
@@ -1504,7 +1506,7 @@ static void __prep_new_huge_page(struct page *page)
static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
{
- __prep_new_huge_page(page);
+ __prep_new_huge_page(h, page);
spin_lock_irq(&hugetlb_lock);
__prep_account_new_huge_page(h, nid);
spin_unlock_irq(&hugetlb_lock);
@@ -2351,14 +2353,15 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
/*
* Before dissolving the page, we need to allocate a new one for the
- * pool to remain stable. Using alloc_buddy_huge_page() allows us to
- * not having to deal with prep_new_huge_page() and avoids dealing of any
- * counters. This simplifies and let us do the whole thing under the
- * lock.
+ * pool to remain stable. Here, we allocate the page and 'prep' it
+ * by doing everything but actually updating counters and adding to
+ * the pool. This simplifies and let us do most of the processing
+ * under the lock.
*/
new_page = alloc_buddy_huge_page(h, gfp_mask, nid, NULL, NULL);
if (!new_page)
return -ENOMEM;
+ __prep_new_huge_page(h, new_page);
retry:
spin_lock_irq(&hugetlb_lock);
@@ -2397,14 +2400,9 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
remove_hugetlb_page(h, old_page, false);
/*
- * new_page needs to be initialized with the standard hugetlb
- * state. This is normally done by prep_new_huge_page() but
- * that takes hugetlb_lock which is already held so we need to
- * open code it here.
* Reference count trick is needed because allocator gives us
* referenced page but the pool requires pages with 0 refcount.
*/
- __prep_new_huge_page(new_page);
__prep_account_new_huge_page(h, nid);
page_ref_dec(new_page);
enqueue_huge_page(h, new_page);
@@ -2420,7 +2418,7 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
free_new:
spin_unlock_irq(&hugetlb_lock);
- __free_pages(new_page, huge_page_order(h));
+ update_and_free_page(h, new_page);
return ret;
}
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
new file mode 100644
index 0000000000000000000000000000000000000000..e45a138a7f855832fa7cbb5e88200f2e5586480a
--- /dev/null
+++ b/mm/hugetlb_vmemmap.c
@@ -0,0 +1,218 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Free some vmemmap pages of HugeTLB
+ *
+ * Copyright (c) 2020, Bytedance. All rights reserved.
+ *
+ * Author: Muchun Song <songmuchun@bytedance.com>
+ *
+ * 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.
+ *
+ * HugeTLB pages consist of multiple base page size pages and is supported by
+ * many architectures. See hugetlbpage.rst in the Documentation directory 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.
+ *
+ * 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
+ * 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
+ * to the buddy allocator for other uses.
+ *
+ * Different architectures support different HugeTLB pages. For example, the
+ * following table is the HugeTLB page size supported by x86 and arm64
+ * architectures. Because arm64 supports 4k, 16k, and 64k base pages and
+ * supports contiguous entries, so it supports many kinds of sizes of HugeTLB
+ * page.
+ *
+ * +--------------+-----------+-----------------------------------------------+
+ * | Architecture | Page Size | HugeTLB Page Size |
+ * +--------------+-----------+-----------+-----------+-----------+-----------+
+ * | x86-64 | 4KB | 2MB | 1GB | | |
+ * +--------------+-----------+-----------+-----------+-----------+-----------+
+ * | | 4KB | 64KB | 2MB | 32MB | 1GB |
+ * | +-----------+-----------+-----------+-----------+-----------+
+ * | arm64 | 16KB | 2MB | 32MB | 1GB | |
+ * | +-----------+-----------+-----------+-----------+-----------+
+ * | | 64KB | 2MB | 512MB | 16GB | |
+ * +--------------+-----------+-----------+-----------+-----------+-----------+
+ *
+ * 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
+ *
+ * Where HugeTLB_Size is the size of the HugeTLB page. We know that the size
+ * of the HugeTLB page is always n times PAGE_SIZE. So we can get the following
+ * relationship.
+ *
+ * HugeTLB_Size = n * PAGE_SIZE
+ *
+ * Then,
+ *
+ * struct_size = n * PAGE_SIZE / PAGE_SIZE * sizeof(struct page) / PAGE_SIZE
+ * = n * sizeof(struct page) / PAGE_SIZE
+ *
+ * We can use huge mapping at the pud/pmd level for the HugeTLB page.
+ *
+ * For the HugeTLB page of the pmd level mapping, then
+ *
+ * struct_size = n * sizeof(struct page) / PAGE_SIZE
+ * = PAGE_SIZE / sizeof(pte_t) * sizeof(struct page) / PAGE_SIZE
+ * = sizeof(struct page) / sizeof(pte_t)
+ * = 64 / 8
+ * = 8 (pages)
+ *
+ * Where n is how many pte entries which one page can contains. So the value of
+ * 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.
+ * 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 the base page.
+ *
+ * For the HugeTLB page of the pud level mapping, then
+ *
+ * struct_size = PAGE_SIZE / sizeof(pmd_t) * struct_size(pmd)
+ * = PAGE_SIZE / 8 * 8 (pages)
+ * = PAGE_SIZE (pages)
+ *
+ * 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
+ * HugeTLB page consists in 4096.
+ *
+ * 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.
+ *
+ * Here is how things look before optimization.
+ *
+ * HugeTLB struct pages(8 pages) page frame(8 pages)
+ * +-----------+ ---virt_to_page---> +-----------+ mapping to +-----------+
+ * | | | 0 | -------------> | 0 |
+ * | | +-----------+ +-----------+
+ * | | | 1 | -------------> | 1 |
+ * | | +-----------+ +-----------+
+ * | | | 2 | -------------> | 2 |
+ * | | +-----------+ +-----------+
+ * | | | 3 | -------------> | 3 |
+ * | | +-----------+ +-----------+
+ * | | | 4 | -------------> | 4 |
+ * | PMD | +-----------+ +-----------+
+ * | level | | 5 | -------------> | 5 |
+ * | mapping | +-----------+ +-----------+
+ * | | | 6 | -------------> | 6 |
+ * | | +-----------+ +-----------+
+ * | | | 7 | -------------> | 7 |
+ * | | +-----------+ +-----------+
+ * | |
+ * | |
+ * | |
+ * +-----------+
+ *
+ * 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 2 to 7 to page 1. Only 2 pages of page structs
+ * will be used for each HugeTLB page. This will allow us to free the remaining
+ * 6 pages to the buddy allocator.
+ *
+ * Here is how things look after remapping.
+ *
+ * HugeTLB struct pages(8 pages) page frame(8 pages)
+ * +-----------+ ---virt_to_page---> +-----------+ mapping to +-----------+
+ * | | | 0 | -------------> | 0 |
+ * | | +-----------+ +-----------+
+ * | | | 1 | -------------> | 1 |
+ * | | +-----------+ +-----------+
+ * | | | 2 | ----------------^ ^ ^ ^ ^ ^
+ * | | +-----------+ | | | | |
+ * | | | 3 | ------------------+ | | | |
+ * | | +-----------+ | | | |
+ * | | | 4 | --------------------+ | | |
+ * | PMD | +-----------+ | | |
+ * | level | | 5 | ----------------------+ | |
+ * | mapping | +-----------+ | |
+ * | | | 6 | ------------------------+ |
+ * | | +-----------+ |
+ * | | | 7 | --------------------------+
+ * | | +-----------+
+ * | |
+ * | |
+ * | |
+ * +-----------+
+ *
+ * When a HugeTLB is freed to the buddy system, we should allocate 6 pages for
+ * vmemmap pages and restore the previous mapping relationship.
+ *
+ * For the HugeTLB page of the pud level mapping. It is similar to the former.
+ * We also can use this approach to free (PAGE_SIZE - 2) vmemmap pages.
+ *
+ * Apart from the HugeTLB page of the pmd/pud level mapping, some architectures
+ * (e.g. aarch64) provides a contiguous bit in the translation table entries
+ * that hints to the MMU to indicate that it is one of a contiguous set of
+ * entries that can be cached in a single TLB entry.
+ *
+ * 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 2 pages.
+ */
+#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 tail page structures. We map the virtual addresses of the remaining
+ * pages of tail page structures to the first tail page struct, and then free
+ * these page frames. Therefore, we need to reserve two pages as vmemmap areas.
+ */
+#define RESERVE_VMEMMAP_NR 2U
+#define RESERVE_VMEMMAP_SIZE (RESERVE_VMEMMAP_NR << PAGE_SHIFT)
+
+/*
+ * How many vmemmap pages associated with a HugeTLB page that can be freed
+ * to the buddy allocator.
+ *
+ * Todo: Returns zero for now, which means the feature is disabled. We will
+ * enable it once all the infrastructure is there.
+ */
+static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
+{
+ return 0;
+}
+
+static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
+{
+ return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
+}
+
+void free_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+ unsigned long vmemmap_addr = (unsigned long)head;
+ unsigned long vmemmap_end, vmemmap_reuse;
+
+ if (!free_vmemmap_pages_per_hpage(h))
+ return;
+
+ vmemmap_addr += RESERVE_VMEMMAP_SIZE;
+ vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h);
+ vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
+
+ /*
+ * Remap the vmemmap virtual address range [@vmemmap_addr, @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.
+ */
+ vmemmap_remap_free(vmemmap_addr, vmemmap_end, vmemmap_reuse);
+}
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
new file mode 100644
index 0000000000000000000000000000000000000000..6923f03534d50be78ef79948767af9bc3a96a33f
--- /dev/null
+++ b/mm/hugetlb_vmemmap.h
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Free some vmemmap pages of HugeTLB
+ *
+ * Copyright (c) 2020, Bytedance. All rights reserved.
+ *
+ * Author: Muchun Song <songmuchun@bytedance.com>
+ */
+#ifndef _LINUX_HUGETLB_VMEMMAP_H
+#define _LINUX_HUGETLB_VMEMMAP_H
+#include <linux/hugetlb.h>
+
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+void free_huge_page_vmemmap(struct hstate *h, struct page *head);
+#else
+static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+}
+#endif /* CONFIG_HUGETLB_PAGE_FREE_VMEMMAP */
+#endif /* _LINUX_HUGETLB_VMEMMAP_H */
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 16183d85a7d505538a14bc1d958ae672a547148d..3ec5488c815cd7403c948f92076ccac63901ddd8 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -27,8 +27,202 @@
#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>
+
+/**
+ * struct vmemmap_remap_walk - walk vmemmap page table
+ *
+ * @remap_pte: called for each lowest-level entry (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.
+ */
+struct vmemmap_remap_walk {
+ void (*remap_pte)(pte_t *pte, unsigned long addr,
+ struct vmemmap_remap_walk *walk);
+ struct page *reuse_page;
+ unsigned long reuse_addr;
+ struct list_head *vmemmap_pages;
+};
+
+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++;
+ }
+
+ for (; addr != end; addr += PAGE_SIZE, pte++)
+ walk->remap_pte(pte, addr, walk);
+}
+
+static void 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 {
+ BUG_ON(pmd_leaf(*pmd));
+
+ next = pmd_addr_end(addr, end);
+ vmemmap_pte_range(pmd, addr, next, walk);
+ } while (pmd++, addr = next, addr != end);
+}
+
+static void 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 {
+ next = pud_addr_end(addr, end);
+ vmemmap_pmd_range(pud, addr, next, walk);
+ } while (pud++, addr = next, addr != end);
+}
+
+static void 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 {
+ next = p4d_addr_end(addr, end);
+ vmemmap_pud_range(p4d, addr, next, walk);
+ } while (p4d++, addr = next, addr != end);
+}
+
+static void 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(!IS_ALIGNED(start, PAGE_SIZE));
+ VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));
+
+ pgd = pgd_offset_k(addr);
+ do {
+ next = pgd_addr_end(addr, end);
+ vmemmap_p4d_range(pgd, addr, next, walk);
+ } 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);
+}
+
+/*
+ * 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(&page->lru, walk->vmemmap_pages);
+ set_pte_at(&init_mm, addr, pte, entry);
+}
+
+/**
+ * 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.
+ *
+ * Note: This function depends on vmemmap being base page mapped. Please make
+ * sure that we disable PMD mapping of vmemmap pages when calling this function.
+ */
+void vmemmap_remap_free(unsigned long start, unsigned long end,
+ unsigned long reuse)
+{
+ 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);
+
+ vmemmap_remap_range(reuse, end, &walk);
+ free_vmemmap_page_list(&vmemmap_pages);
+}
/*
* Allocate a block of memory to be used to back the virtual memory map