| // SPDX-License-Identifier: GPL-2.0 |
| /* |
| * HugeTLB Vmemmap Optimization (HVO) |
| * |
| * Copyright (c) 2020, ByteDance. All rights reserved. |
| * |
| * Author: Muchun Song <songmuchun@bytedance.com> |
| * |
| * See Documentation/mm/vmemmap_dedup.rst |
| */ |
| #define pr_fmt(fmt) "HugeTLB: " fmt |
| |
| #include <linux/pgtable.h> |
| #include <linux/moduleparam.h> |
| #include <linux/bootmem_info.h> |
| #include <asm/pgalloc.h> |
| #include <asm/tlbflush.h> |
| #include "hugetlb_vmemmap.h" |
| |
| /** |
| * 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 < PTRS_PER_PTE; 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); |
| |
| flush_tlb_kernel_range(start, 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) |
| 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; |
| struct page *page = pte_page(*pte); |
| pte_t entry; |
| |
| /* Remapping the head page requires r/w */ |
| if (unlikely(addr == walk->reuse_addr)) { |
| pgprot = PAGE_KERNEL; |
| list_del(&walk->reuse_page->lru); |
| |
| /* |
| * Makes sure that preceding stores to the page contents from |
| * vmemmap_remap_free() become visible before the set_pte_at() |
| * write. |
| */ |
| smp_wmb(); |
| } |
| |
| entry = mk_pte(walk->reuse_page, pgprot); |
| 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_page_prepare(). 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) |
| { |
| struct page *from = start + NR_RESET_STRUCT_PAGE; |
| |
| BUILD_BUG_ON(NR_RESET_STRUCT_PAGE * 2 > PAGE_SIZE / sizeof(struct page)); |
| memcpy(start, from, sizeof(*from) * NR_RESET_STRUCT_PAGE); |
| } |
| |
| 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); |
| |
| /* |
| * Makes sure that preceding stores to the page contents become visible |
| * before the set_pte_at() write. |
| */ |
| smp_wmb(); |
| 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; |
| LIST_HEAD(vmemmap_pages); |
| struct vmemmap_remap_walk walk = { |
| .remap_pte = vmemmap_remap_pte, |
| .reuse_addr = reuse, |
| .vmemmap_pages = &vmemmap_pages, |
| }; |
| int nid = page_to_nid((struct page *)start); |
| gfp_t gfp_mask = GFP_KERNEL | __GFP_THISNODE | __GFP_NORETRY | |
| __GFP_NOWARN; |
| |
| /* |
| * Allocate a new head vmemmap page to avoid breaking a contiguous |
| * block of struct page memory when freeing it back to page allocator |
| * in free_vmemmap_page_list(). This will allow the likely contiguous |
| * struct page backing memory to be kept contiguous and allowing for |
| * more allocations of hugepages. Fallback to the currently |
| * mapped head page in case should it fail to allocate. |
| */ |
| walk.reuse_page = alloc_pages_node(nid, gfp_mask, 0); |
| if (walk.reuse_page) { |
| copy_page(page_to_virt(walk.reuse_page), |
| (void *)walk.reuse_addr); |
| list_add(&walk.reuse_page->lru, &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_page(page); |
| 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_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_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_start, vmemmap_end, vmemmap_reuse, |
| GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE); |
| if (!ret) { |
| ClearHPageVmemmapOptimized(head); |
| static_branch_dec(&hugetlb_optimize_vmemmap_key); |
| } |
| |
| return ret; |
| } |
| |
| /* 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_enabled)) |
| return false; |
| |
| if (!hugetlb_vmemmap_optimizable(h)) |
| return false; |
| |
| if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) { |
| pmd_t *pmdp, pmd; |
| struct page *vmemmap_page; |
| unsigned long vaddr = (unsigned long)head; |
| |
| /* |
| * Only the vmemmap page's vmemmap page can be self-hosted. |
| * Walking the page tables to find the backing page of the |
| * vmemmap page. |
| */ |
| pmdp = pmd_off_k(vaddr); |
| /* |
| * The READ_ONCE() is used to stabilize *pmdp in a register or |
| * on the stack so that it will stop changing under the code. |
| * The only concurrent operation where it can be changed is |
| * split_vmemmap_huge_pmd() (*pmdp will be stable after this |
| * operation). |
| */ |
| pmd = READ_ONCE(*pmdp); |
| if (pmd_leaf(pmd)) |
| vmemmap_page = pmd_page(pmd) + pte_index(vaddr); |
| else |
| vmemmap_page = pte_page(*pte_offset_kernel(pmdp, vaddr)); |
| /* |
| * Due to HugeTLB alignment requirements and the vmemmap pages |
| * being at the start of the hotplugged memory region in |
| * memory_hotplug.memmap_on_memory case. Checking any vmemmap |
| * page's vmemmap page if it is marked as VmemmapSelfHosted is |
| * sufficient. |
| * |
| * [ hotplugged memory ] |
| * [ section ][...][ section ] |
| * [ vmemmap ][ usable memory ] |
| * ^ | | | |
| * +---+ | | |
| * ^ | | |
| * +-------+ | |
| * ^ | |
| * +-------------------------------------------+ |
| */ |
| if (PageVmemmapSelfHosted(vmemmap_page)) |
| return false; |
| } |
| |
| return true; |
| } |
| |
| /** |
| * 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_start = (unsigned long)head, vmemmap_end; |
| unsigned long vmemmap_reuse; |
| |
| if (!vmemmap_should_optimize(h, head)) |
| return; |
| |
| static_branch_inc(&hugetlb_optimize_vmemmap_key); |
| |
| 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_start, @vmemmap_end) |
| * to the page which @vmemmap_reuse is mapped to, then free the pages |
| * which the range [@vmemmap_start, @vmemmap_end] is mapped to. |
| */ |
| if (vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse)) |
| static_branch_dec(&hugetlb_optimize_vmemmap_key); |
| else |
| SetHPageVmemmapOptimized(head); |
| } |
| |
| static struct ctl_table hugetlb_vmemmap_sysctls[] = { |
| { |
| .procname = "hugetlb_optimize_vmemmap", |
| .data = &vmemmap_optimize_enabled, |
| .maxlen = sizeof(vmemmap_optimize_enabled), |
| .mode = 0644, |
| .proc_handler = proc_dobool, |
| }, |
| { } |
| }; |
| |
| static int __init hugetlb_vmemmap_init(void) |
| { |
| const struct hstate *h; |
| |
| /* HUGETLB_VMEMMAP_RESERVE_SIZE should cover all used struct pages */ |
| BUILD_BUG_ON(__NR_USED_SUBPAGE * sizeof(struct page) > HUGETLB_VMEMMAP_RESERVE_SIZE); |
| |
| for_each_hstate(h) { |
| if (hugetlb_vmemmap_optimizable(h)) { |
| register_sysctl_init("vm", hugetlb_vmemmap_sysctls); |
| break; |
| } |
| } |
| return 0; |
| } |
| late_initcall(hugetlb_vmemmap_init); |