/* * Copyright (C) 2009 Red Hat, Inc. * * This work is licensed under the terms of the GNU GPL, version 2. See * the COPYING file in the top-level directory. */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "internal.h" /* * By default transparent hugepage support is disabled in order that avoid * to risk increase the memory footprint of applications without a guaranteed * benefit. When transparent hugepage support is enabled, is for all mappings, * and khugepaged scans all mappings. * Defrag is invoked by khugepaged hugepage allocations and by page faults * for all hugepage allocations. */ unsigned long transparent_hugepage_flags __read_mostly = #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS (1<flags)) return READ_ONCE(huge_zero_page); if (!get_huge_zero_page()) return NULL; if (test_and_set_bit(MMF_HUGE_ZERO_PAGE, &mm->flags)) put_huge_zero_page(); return READ_ONCE(huge_zero_page); } void mm_put_huge_zero_page(struct mm_struct *mm) { if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags)) put_huge_zero_page(); } static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink, struct shrink_control *sc) { /* we can free zero page only if last reference remains */ return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0; } static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink, struct shrink_control *sc) { if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) { struct page *zero_page = xchg(&huge_zero_page, NULL); BUG_ON(zero_page == NULL); __free_pages(zero_page, compound_order(zero_page)); return HPAGE_PMD_NR; } return 0; } static struct shrinker huge_zero_page_shrinker = { .count_objects = shrink_huge_zero_page_count, .scan_objects = shrink_huge_zero_page_scan, .seeks = DEFAULT_SEEKS, }; #ifdef CONFIG_SYSFS static ssize_t triple_flag_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count, enum transparent_hugepage_flag enabled, enum transparent_hugepage_flag deferred, enum transparent_hugepage_flag req_madv) { if (!memcmp("defer", buf, min(sizeof("defer")-1, count))) { if (enabled == deferred) return -EINVAL; clear_bit(enabled, &transparent_hugepage_flags); clear_bit(req_madv, &transparent_hugepage_flags); set_bit(deferred, &transparent_hugepage_flags); } else if (!memcmp("always", buf, min(sizeof("always")-1, count))) { clear_bit(deferred, &transparent_hugepage_flags); clear_bit(req_madv, &transparent_hugepage_flags); set_bit(enabled, &transparent_hugepage_flags); } else if (!memcmp("madvise", buf, min(sizeof("madvise")-1, count))) { clear_bit(enabled, &transparent_hugepage_flags); clear_bit(deferred, &transparent_hugepage_flags); set_bit(req_madv, &transparent_hugepage_flags); } else if (!memcmp("never", buf, min(sizeof("never")-1, count))) { clear_bit(enabled, &transparent_hugepage_flags); clear_bit(req_madv, &transparent_hugepage_flags); clear_bit(deferred, &transparent_hugepage_flags); } else return -EINVAL; return count; } static ssize_t enabled_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { if (test_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags)) return sprintf(buf, "[always] madvise never\n"); else if (test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags)) return sprintf(buf, "always [madvise] never\n"); else return sprintf(buf, "always madvise [never]\n"); } static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count) { ssize_t ret; ret = triple_flag_store(kobj, attr, buf, count, TRANSPARENT_HUGEPAGE_FLAG, TRANSPARENT_HUGEPAGE_FLAG, TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG); if (ret > 0) { int err = start_stop_khugepaged(); if (err) ret = err; } return ret; } static struct kobj_attribute enabled_attr = __ATTR(enabled, 0644, enabled_show, enabled_store); ssize_t single_hugepage_flag_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf, enum transparent_hugepage_flag flag) { return sprintf(buf, "%d\n", !!test_bit(flag, &transparent_hugepage_flags)); } ssize_t single_hugepage_flag_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count, enum transparent_hugepage_flag flag) { unsigned long value; int ret; ret = kstrtoul(buf, 10, &value); if (ret < 0) return ret; if (value > 1) return -EINVAL; if (value) set_bit(flag, &transparent_hugepage_flags); else clear_bit(flag, &transparent_hugepage_flags); return count; } /* * Currently defrag only disables __GFP_NOWAIT for allocation. A blind * __GFP_REPEAT is too aggressive, it's never worth swapping tons of * memory just to allocate one more hugepage. */ static ssize_t defrag_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags)) return sprintf(buf, "[always] defer madvise never\n"); if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags)) return sprintf(buf, "always [defer] madvise never\n"); else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags)) return sprintf(buf, "always defer [madvise] never\n"); else return sprintf(buf, "always defer madvise [never]\n"); } static ssize_t defrag_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count) { return triple_flag_store(kobj, attr, buf, count, TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG); } static struct kobj_attribute defrag_attr = __ATTR(defrag, 0644, defrag_show, defrag_store); static ssize_t use_zero_page_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { return single_hugepage_flag_show(kobj, attr, buf, TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG); } static ssize_t use_zero_page_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count) { return single_hugepage_flag_store(kobj, attr, buf, count, TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG); } static struct kobj_attribute use_zero_page_attr = __ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store); #ifdef CONFIG_DEBUG_VM static ssize_t debug_cow_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { return single_hugepage_flag_show(kobj, attr, buf, TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG); } static ssize_t debug_cow_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count) { return single_hugepage_flag_store(kobj, attr, buf, count, TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG); } static struct kobj_attribute debug_cow_attr = __ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store); #endif /* CONFIG_DEBUG_VM */ static struct attribute *hugepage_attr[] = { &enabled_attr.attr, &defrag_attr.attr, &use_zero_page_attr.attr, #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE) &shmem_enabled_attr.attr, #endif #ifdef CONFIG_DEBUG_VM &debug_cow_attr.attr, #endif NULL, }; static struct attribute_group hugepage_attr_group = { .attrs = hugepage_attr, }; static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj) { int err; *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj); if (unlikely(!*hugepage_kobj)) { pr_err("failed to create transparent hugepage kobject\n"); return -ENOMEM; } err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group); if (err) { pr_err("failed to register transparent hugepage group\n"); goto delete_obj; } err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group); if (err) { pr_err("failed to register transparent hugepage group\n"); goto remove_hp_group; } return 0; remove_hp_group: sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group); delete_obj: kobject_put(*hugepage_kobj); return err; } static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj) { sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group); sysfs_remove_group(hugepage_kobj, &hugepage_attr_group); kobject_put(hugepage_kobj); } #else static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj) { return 0; } static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj) { } #endif /* CONFIG_SYSFS */ static int __init hugepage_init(void) { int err; struct kobject *hugepage_kobj; if (!has_transparent_hugepage()) { transparent_hugepage_flags = 0; return -EINVAL; } /* * hugepages can't be allocated by the buddy allocator */ MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER >= MAX_ORDER); /* * we use page->mapping and page->index in second tail page * as list_head: assuming THP order >= 2 */ MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER < 2); err = hugepage_init_sysfs(&hugepage_kobj); if (err) goto err_sysfs; err = khugepaged_init(); if (err) goto err_slab; err = register_shrinker(&huge_zero_page_shrinker); if (err) goto err_hzp_shrinker; err = register_shrinker(&deferred_split_shrinker); if (err) goto err_split_shrinker; /* * By default disable transparent hugepages on smaller systems, * where the extra memory used could hurt more than TLB overhead * is likely to save. The admin can still enable it through /sys. */ if (totalram_pages < (512 << (20 - PAGE_SHIFT))) { transparent_hugepage_flags = 0; return 0; } err = start_stop_khugepaged(); if (err) goto err_khugepaged; return 0; err_khugepaged: unregister_shrinker(&deferred_split_shrinker); err_split_shrinker: unregister_shrinker(&huge_zero_page_shrinker); err_hzp_shrinker: khugepaged_destroy(); err_slab: hugepage_exit_sysfs(hugepage_kobj); err_sysfs: return err; } subsys_initcall(hugepage_init); static int __init setup_transparent_hugepage(char *str) { int ret = 0; if (!str) goto out; if (!strcmp(str, "always")) { set_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags); clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags); ret = 1; } else if (!strcmp(str, "madvise")) { clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags); set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags); ret = 1; } else if (!strcmp(str, "never")) { clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags); clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags); ret = 1; } out: if (!ret) pr_warn("transparent_hugepage= cannot parse, ignored\n"); return ret; } __setup("transparent_hugepage=", setup_transparent_hugepage); pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma) { if (likely(vma->vm_flags & VM_WRITE)) pmd = pmd_mkwrite(pmd); return pmd; } static inline struct list_head *page_deferred_list(struct page *page) { /* * ->lru in the tail pages is occupied by compound_head. * Let's use ->mapping + ->index in the second tail page as list_head. */ return (struct list_head *)&page[2].mapping; } void prep_transhuge_page(struct page *page) { /* * we use page->mapping and page->indexlru in second tail page * as list_head: assuming THP order >= 2 */ INIT_LIST_HEAD(page_deferred_list(page)); set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR); } unsigned long __thp_get_unmapped_area(struct file *filp, unsigned long len, loff_t off, unsigned long flags, unsigned long size) { unsigned long addr; loff_t off_end = off + len; loff_t off_align = round_up(off, size); unsigned long len_pad; if (off_end <= off_align || (off_end - off_align) < size) return 0; len_pad = len + size; if (len_pad < len || (off + len_pad) < off) return 0; addr = current->mm->get_unmapped_area(filp, 0, len_pad, off >> PAGE_SHIFT, flags); if (IS_ERR_VALUE(addr)) return 0; addr += (off - addr) & (size - 1); return addr; } unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr, unsigned long len, unsigned long pgoff, unsigned long flags) { loff_t off = (loff_t)pgoff << PAGE_SHIFT; if (addr) goto out; if (!IS_DAX(filp->f_mapping->host) || !IS_ENABLED(CONFIG_FS_DAX_PMD)) goto out; addr = __thp_get_unmapped_area(filp, len, off, flags, PMD_SIZE); if (addr) return addr; out: return current->mm->get_unmapped_area(filp, addr, len, pgoff, flags); } EXPORT_SYMBOL_GPL(thp_get_unmapped_area); static int __do_huge_pmd_anonymous_page(struct fault_env *fe, struct page *page, gfp_t gfp) { struct vm_area_struct *vma = fe->vma; struct mem_cgroup *memcg; pgtable_t pgtable; unsigned long haddr = fe->address & HPAGE_PMD_MASK; VM_BUG_ON_PAGE(!PageCompound(page), page); if (mem_cgroup_try_charge(page, vma->vm_mm, gfp | __GFP_NORETRY, &memcg, true)) { put_page(page); count_vm_event(THP_FAULT_FALLBACK); return VM_FAULT_FALLBACK; } pgtable = pte_alloc_one(vma->vm_mm, haddr); if (unlikely(!pgtable)) { mem_cgroup_cancel_charge(page, memcg, true); put_page(page); return VM_FAULT_OOM; } clear_huge_page(page, haddr, HPAGE_PMD_NR); /* * The memory barrier inside __SetPageUptodate makes sure that * clear_huge_page writes become visible before the set_pmd_at() * write. */ __SetPageUptodate(page); fe->ptl = pmd_lock(vma->vm_mm, fe->pmd); if (unlikely(!pmd_none(*fe->pmd))) { spin_unlock(fe->ptl); mem_cgroup_cancel_charge(page, memcg, true); put_page(page); pte_free(vma->vm_mm, pgtable); } else { pmd_t entry; /* Deliver the page fault to userland */ if (userfaultfd_missing(vma)) { int ret; spin_unlock(fe->ptl); mem_cgroup_cancel_charge(page, memcg, true); put_page(page); pte_free(vma->vm_mm, pgtable); ret = handle_userfault(fe, VM_UFFD_MISSING); VM_BUG_ON(ret & VM_FAULT_FALLBACK); return ret; } entry = mk_huge_pmd(page, vma->vm_page_prot); entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); page_add_new_anon_rmap(page, vma, haddr, true); mem_cgroup_commit_charge(page, memcg, false, true); lru_cache_add_active_or_unevictable(page, vma); pgtable_trans_huge_deposit(vma->vm_mm, fe->pmd, pgtable); set_pmd_at(vma->vm_mm, haddr, fe->pmd, entry); add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR); atomic_long_inc(&vma->vm_mm->nr_ptes); spin_unlock(fe->ptl); count_vm_event(THP_FAULT_ALLOC); } return 0; } /* * If THP defrag is set to always then directly reclaim/compact as necessary * If set to defer then do only background reclaim/compact and defer to khugepaged * If set to madvise and the VMA is flagged then directly reclaim/compact * When direct reclaim/compact is allowed, don't retry except for flagged VMA's */ static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma) { gfp_t gfp = GFP_TRANSHUGE_LIGHT; bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE); if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags) && vma_madvised) gfp = GFP_TRANSHUGE; else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags)) gfp = GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM; else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags)) gfp = GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY); /* Disable movable allocations to avoid fallback to CMA. * Unmovable allocations can fallback to movable anyway. */ gfp &= ~__GFP_MOVABLE; return gfp; } /* Caller must hold page table lock. */ static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm, struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd, struct page *zero_page) { pmd_t entry; if (!pmd_none(*pmd)) return false; entry = mk_pmd(zero_page, vma->vm_page_prot); entry = pmd_mkhuge(entry); if (pgtable) pgtable_trans_huge_deposit(mm, pmd, pgtable); set_pmd_at(mm, haddr, pmd, entry); atomic_long_inc(&mm->nr_ptes); return true; } int do_huge_pmd_anonymous_page(struct fault_env *fe) { struct vm_area_struct *vma = fe->vma; gfp_t gfp; struct page *page; unsigned long haddr = fe->address & HPAGE_PMD_MASK; if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end) return VM_FAULT_FALLBACK; if (unlikely(anon_vma_prepare(vma))) return VM_FAULT_OOM; if (unlikely(khugepaged_enter(vma, vma->vm_flags))) return VM_FAULT_OOM; if (!(fe->flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(vma->vm_mm) && transparent_hugepage_use_zero_page()) { pgtable_t pgtable; struct page *zero_page; int ret; pgtable = pte_alloc_one(vma->vm_mm, haddr); if (unlikely(!pgtable)) return VM_FAULT_OOM; zero_page = mm_get_huge_zero_page(vma->vm_mm); if (unlikely(!zero_page)) { pte_free(vma->vm_mm, pgtable); count_vm_event(THP_FAULT_FALLBACK); return VM_FAULT_FALLBACK; } fe->ptl = pmd_lock(vma->vm_mm, fe->pmd); ret = 0; if (pmd_none(*fe->pmd)) { if (userfaultfd_missing(vma)) { spin_unlock(fe->ptl); pte_free(vma->vm_mm, pgtable); ret = handle_userfault(fe, VM_UFFD_MISSING); VM_BUG_ON(ret & VM_FAULT_FALLBACK); } else { set_huge_zero_page(pgtable, vma->vm_mm, vma, haddr, fe->pmd, zero_page); spin_unlock(fe->ptl); } } else { spin_unlock(fe->ptl); pte_free(vma->vm_mm, pgtable); } return ret; } gfp = alloc_hugepage_direct_gfpmask(vma); page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER); if (unlikely(!page)) { count_vm_event(THP_FAULT_FALLBACK); return VM_FAULT_FALLBACK; } prep_transhuge_page(page); return __do_huge_pmd_anonymous_page(fe, page, gfp); } static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write) { struct mm_struct *mm = vma->vm_mm; pmd_t entry; spinlock_t *ptl; ptl = pmd_lock(mm, pmd); entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); if (pfn_t_devmap(pfn)) entry = pmd_mkdevmap(entry); if (write) { entry = pmd_mkyoung(pmd_mkdirty(entry)); entry = maybe_pmd_mkwrite(entry, vma); } set_pmd_at(mm, addr, pmd, entry); update_mmu_cache_pmd(vma, addr, pmd); spin_unlock(ptl); } int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, pmd_t *pmd, pfn_t pfn, bool write) { pgprot_t pgprot = vma->vm_page_prot; /* * If we had pmd_special, we could avoid all these restrictions, * but we need to be consistent with PTEs and architectures that * can't support a 'special' bit. */ BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))); BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) == (VM_PFNMAP|VM_MIXEDMAP)); BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags)); BUG_ON(!pfn_t_devmap(pfn)); if (addr < vma->vm_start || addr >= vma->vm_end) return VM_FAULT_SIGBUS; if (track_pfn_insert(vma, &pgprot, pfn)) return VM_FAULT_SIGBUS; insert_pfn_pmd(vma, addr, pmd, pfn, pgprot, write); return VM_FAULT_NOPAGE; } EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd); static void touch_pmd(struct vm_area_struct *vma, unsigned long addr, pmd_t *pmd, int flags) { pmd_t _pmd; _pmd = pmd_mkyoung(*pmd); if (flags & FOLL_WRITE) _pmd = pmd_mkdirty(_pmd); if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK, pmd, _pmd, flags & FOLL_WRITE)) update_mmu_cache_pmd(vma, addr, pmd); } struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr, pmd_t *pmd, int flags) { unsigned long pfn = pmd_pfn(*pmd); struct mm_struct *mm = vma->vm_mm; struct dev_pagemap *pgmap; struct page *page; assert_spin_locked(pmd_lockptr(mm, pmd)); /* * When we COW a devmap PMD entry, we split it into PTEs, so we should * not be in this function with `flags & FOLL_COW` set. */ WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set"); if (flags & FOLL_WRITE && !pmd_write(*pmd)) return NULL; if (pmd_present(*pmd) && pmd_devmap(*pmd)) /* pass */; else return NULL; if (flags & FOLL_TOUCH) touch_pmd(vma, addr, pmd, flags); /* * device mapped pages can only be returned if the * caller will manage the page reference count. */ if (!(flags & FOLL_GET)) return ERR_PTR(-EEXIST); pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT; pgmap = get_dev_pagemap(pfn, NULL); if (!pgmap) return ERR_PTR(-EFAULT); page = pfn_to_page(pfn); get_page(page); put_dev_pagemap(pgmap); return page; } int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr, struct vm_area_struct *vma) { spinlock_t *dst_ptl, *src_ptl; struct page *src_page; pmd_t pmd; pgtable_t pgtable = NULL; int ret = -ENOMEM; /* Skip if can be re-fill on fault */ if (!vma_is_anonymous(vma)) return 0; pgtable = pte_alloc_one(dst_mm, addr); if (unlikely(!pgtable)) goto out; dst_ptl = pmd_lock(dst_mm, dst_pmd); src_ptl = pmd_lockptr(src_mm, src_pmd); spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); ret = -EAGAIN; pmd = *src_pmd; if (unlikely(!pmd_trans_huge(pmd))) { pte_free(dst_mm, pgtable); goto out_unlock; } /* * When page table lock is held, the huge zero pmd should not be * under splitting since we don't split the page itself, only pmd to * a page table. */ if (is_huge_zero_pmd(pmd)) { struct page *zero_page; /* * get_huge_zero_page() will never allocate a new page here, * since we already have a zero page to copy. It just takes a * reference. */ zero_page = mm_get_huge_zero_page(dst_mm); set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd, zero_page); ret = 0; goto out_unlock; } src_page = pmd_page(pmd); VM_BUG_ON_PAGE(!PageHead(src_page), src_page); get_page(src_page); page_dup_rmap(src_page, true); add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR); atomic_long_inc(&dst_mm->nr_ptes); pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable); pmdp_set_wrprotect(src_mm, addr, src_pmd); pmd = pmd_mkold(pmd_wrprotect(pmd)); set_pmd_at(dst_mm, addr, dst_pmd, pmd); ret = 0; out_unlock: spin_unlock(src_ptl); spin_unlock(dst_ptl); out: return ret; } void huge_pmd_set_accessed(struct fault_env *fe, pmd_t orig_pmd) { pmd_t entry; unsigned long haddr; bool write = fe->flags & FAULT_FLAG_WRITE; fe->ptl = pmd_lock(fe->vma->vm_mm, fe->pmd); if (unlikely(!pmd_same(*fe->pmd, orig_pmd))) goto unlock; entry = pmd_mkyoung(orig_pmd); if (write) entry = pmd_mkdirty(entry); haddr = fe->address & HPAGE_PMD_MASK; if (pmdp_set_access_flags(fe->vma, haddr, fe->pmd, entry, write)) update_mmu_cache_pmd(fe->vma, fe->address, fe->pmd); unlock: spin_unlock(fe->ptl); } static int do_huge_pmd_wp_page_fallback(struct fault_env *fe, pmd_t orig_pmd, struct page *page) { struct vm_area_struct *vma = fe->vma; unsigned long haddr = fe->address & HPAGE_PMD_MASK; struct mem_cgroup *memcg; pgtable_t pgtable; pmd_t _pmd; int ret = 0, i; struct page **pages; unsigned long mmun_start; /* For mmu_notifiers */ unsigned long mmun_end; /* For mmu_notifiers */ pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR, GFP_KERNEL); if (unlikely(!pages)) { ret |= VM_FAULT_OOM; goto out; } for (i = 0; i < HPAGE_PMD_NR; i++) { pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE | __GFP_OTHER_NODE, vma, fe->address, page_to_nid(page)); if (unlikely(!pages[i] || mem_cgroup_try_charge(pages[i], vma->vm_mm, GFP_KERNEL, &memcg, false))) { if (pages[i]) put_page(pages[i]); while (--i >= 0) { memcg = (void *)page_private(pages[i]); set_page_private(pages[i], 0); mem_cgroup_cancel_charge(pages[i], memcg, false); put_page(pages[i]); } kfree(pages); ret |= VM_FAULT_OOM; goto out; } set_page_private(pages[i], (unsigned long)memcg); } for (i = 0; i < HPAGE_PMD_NR; i++) { copy_user_highpage(pages[i], page + i, haddr + PAGE_SIZE * i, vma); __SetPageUptodate(pages[i]); cond_resched(); } mmun_start = haddr; mmun_end = haddr + HPAGE_PMD_SIZE; mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end); fe->ptl = pmd_lock(vma->vm_mm, fe->pmd); if (unlikely(!pmd_same(*fe->pmd, orig_pmd))) goto out_free_pages; VM_BUG_ON_PAGE(!PageHead(page), page); pmdp_huge_clear_flush_notify(vma, haddr, fe->pmd); /* leave pmd empty until pte is filled */ pgtable = pgtable_trans_huge_withdraw(vma->vm_mm, fe->pmd); pmd_populate(vma->vm_mm, &_pmd, pgtable); for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) { pte_t entry; entry = mk_pte(pages[i], vma->vm_page_prot); entry = maybe_mkwrite(pte_mkdirty(entry), vma); memcg = (void *)page_private(pages[i]); set_page_private(pages[i], 0); page_add_new_anon_rmap(pages[i], fe->vma, haddr, false); mem_cgroup_commit_charge(pages[i], memcg, false, false); lru_cache_add_active_or_unevictable(pages[i], vma); fe->pte = pte_offset_map(&_pmd, haddr); VM_BUG_ON(!pte_none(*fe->pte)); set_pte_at(vma->vm_mm, haddr, fe->pte, entry); pte_unmap(fe->pte); } kfree(pages); smp_wmb(); /* make pte visible before pmd */ pmd_populate(vma->vm_mm, fe->pmd, pgtable); page_remove_rmap(page, true); spin_unlock(fe->ptl); mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end); ret |= VM_FAULT_WRITE; put_page(page); out: return ret; out_free_pages: spin_unlock(fe->ptl); mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end); for (i = 0; i < HPAGE_PMD_NR; i++) { memcg = (void *)page_private(pages[i]); set_page_private(pages[i], 0); mem_cgroup_cancel_charge(pages[i], memcg, false); put_page(pages[i]); } kfree(pages); goto out; } int do_huge_pmd_wp_page(struct fault_env *fe, pmd_t orig_pmd) { struct vm_area_struct *vma = fe->vma; struct page *page = NULL, *new_page; struct mem_cgroup *memcg; unsigned long haddr = fe->address & HPAGE_PMD_MASK; unsigned long mmun_start; /* For mmu_notifiers */ unsigned long mmun_end; /* For mmu_notifiers */ gfp_t huge_gfp; /* for allocation and charge */ int ret = 0; fe->ptl = pmd_lockptr(vma->vm_mm, fe->pmd); VM_BUG_ON_VMA(!vma->anon_vma, vma); if (is_huge_zero_pmd(orig_pmd)) goto alloc; spin_lock(fe->ptl); if (unlikely(!pmd_same(*fe->pmd, orig_pmd))) goto out_unlock; page = pmd_page(orig_pmd); VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page); /* * We can only reuse the page if nobody else maps the huge page or it's * part. */ if (page_trans_huge_mapcount(page, NULL) == 1) { pmd_t entry; entry = pmd_mkyoung(orig_pmd); entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); if (pmdp_set_access_flags(vma, haddr, fe->pmd, entry, 1)) update_mmu_cache_pmd(vma, fe->address, fe->pmd); ret |= VM_FAULT_WRITE; goto out_unlock; } get_page(page); spin_unlock(fe->ptl); alloc: if (transparent_hugepage_enabled(vma) && !transparent_hugepage_debug_cow()) { huge_gfp = alloc_hugepage_direct_gfpmask(vma); new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER); } else new_page = NULL; if (likely(new_page)) { prep_transhuge_page(new_page); } else { if (!page) { split_huge_pmd(vma, fe->pmd, fe->address); ret |= VM_FAULT_FALLBACK; } else { ret = do_huge_pmd_wp_page_fallback(fe, orig_pmd, page); if (ret & VM_FAULT_OOM) { split_huge_pmd(vma, fe->pmd, fe->address); ret |= VM_FAULT_FALLBACK; } put_page(page); } count_vm_event(THP_FAULT_FALLBACK); goto out; } if (unlikely(mem_cgroup_try_charge(new_page, vma->vm_mm, huge_gfp | __GFP_NORETRY, &memcg, true))) { put_page(new_page); split_huge_pmd(vma, fe->pmd, fe->address); if (page) put_page(page); ret |= VM_FAULT_FALLBACK; count_vm_event(THP_FAULT_FALLBACK); goto out; } count_vm_event(THP_FAULT_ALLOC); if (!page) clear_huge_page(new_page, haddr, HPAGE_PMD_NR); else copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR); __SetPageUptodate(new_page); mmun_start = haddr; mmun_end = haddr + HPAGE_PMD_SIZE; mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end); spin_lock(fe->ptl); if (page) put_page(page); if (unlikely(!pmd_same(*fe->pmd, orig_pmd))) { spin_unlock(fe->ptl); mem_cgroup_cancel_charge(new_page, memcg, true); put_page(new_page); goto out_mn; } else { pmd_t entry; entry = mk_huge_pmd(new_page, vma->vm_page_prot); entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); pmdp_huge_clear_flush_notify(vma, haddr, fe->pmd); page_add_new_anon_rmap(new_page, vma, haddr, true); mem_cgroup_commit_charge(new_page, memcg, false, true); lru_cache_add_active_or_unevictable(new_page, vma); set_pmd_at(vma->vm_mm, haddr, fe->pmd, entry); update_mmu_cache_pmd(vma, fe->address, fe->pmd); if (!page) { add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR); } else { VM_BUG_ON_PAGE(!PageHead(page), page); page_remove_rmap(page, true); put_page(page); } ret |= VM_FAULT_WRITE; } spin_unlock(fe->ptl); out_mn: mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end); out: return ret; out_unlock: spin_unlock(fe->ptl); return ret; } /* * FOLL_FORCE can write to even unwritable pmd's, but only * after we've gone through a COW cycle and they are dirty. */ static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags) { return pmd_write(pmd) || ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd)); } struct page *follow_trans_huge_pmd(struct vm_area_struct *vma, unsigned long addr, pmd_t *pmd, unsigned int flags) { struct mm_struct *mm = vma->vm_mm; struct page *page = NULL; assert_spin_locked(pmd_lockptr(mm, pmd)); if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags)) goto out; /* Avoid dumping huge zero page */ if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd)) return ERR_PTR(-EFAULT); /* Full NUMA hinting faults to serialise migration in fault paths */ if ((flags & FOLL_NUMA) && pmd_protnone(*pmd)) goto out; page = pmd_page(*pmd); VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page); if (flags & FOLL_TOUCH) touch_pmd(vma, addr, pmd, flags); if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) { /* * We don't mlock() pte-mapped THPs. This way we can avoid * leaking mlocked pages into non-VM_LOCKED VMAs. * * For anon THP: * * In most cases the pmd is the only mapping of the page as we * break COW for the mlock() -- see gup_flags |= FOLL_WRITE for * writable private mappings in populate_vma_page_range(). * * The only scenario when we have the page shared here is if we * mlocking read-only mapping shared over fork(). We skip * mlocking such pages. * * For file THP: * * We can expect PageDoubleMap() to be stable under page lock: * for file pages we set it in page_add_file_rmap(), which * requires page to be locked. */ if (PageAnon(page) && compound_mapcount(page) != 1) goto skip_mlock; if (PageDoubleMap(page) || !page->mapping) goto skip_mlock; if (!trylock_page(page)) goto skip_mlock; lru_add_drain(); if (page->mapping && !PageDoubleMap(page)) mlock_vma_page(page); unlock_page(page); } skip_mlock: page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT; VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page); if (flags & FOLL_GET) get_page(page); out: return page; } /* NUMA hinting page fault entry point for trans huge pmds */ int do_huge_pmd_numa_page(struct fault_env *fe, pmd_t pmd) { struct vm_area_struct *vma = fe->vma; struct anon_vma *anon_vma = NULL; struct page *page; unsigned long haddr = fe->address & HPAGE_PMD_MASK; int page_nid = -1, this_nid = numa_node_id(); int target_nid, last_cpupid = -1; bool page_locked; bool migrated = false; bool was_writable; int flags = 0; fe->ptl = pmd_lock(vma->vm_mm, fe->pmd); if (unlikely(!pmd_same(pmd, *fe->pmd))) goto out_unlock; /* * If there are potential migrations, wait for completion and retry * without disrupting NUMA hinting information. Do not relock and * check_same as the page may no longer be mapped. */ if (unlikely(pmd_trans_migrating(*fe->pmd))) { page = pmd_page(*fe->pmd); if (!get_page_unless_zero(page)) goto out_unlock; spin_unlock(fe->ptl); wait_on_page_locked(page); put_page(page); goto out; } page = pmd_page(pmd); BUG_ON(is_huge_zero_page(page)); page_nid = page_to_nid(page); last_cpupid = page_cpupid_last(page); count_vm_numa_event(NUMA_HINT_FAULTS); if (page_nid == this_nid) { count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL); flags |= TNF_FAULT_LOCAL; } /* See similar comment in do_numa_page for explanation */ if (!pmd_write(pmd)) flags |= TNF_NO_GROUP; /* * Acquire the page lock to serialise THP migrations but avoid dropping * page_table_lock if at all possible */ page_locked = trylock_page(page); target_nid = mpol_misplaced(page, vma, haddr); if (target_nid == -1) { /* If the page was locked, there are no parallel migrations */ if (page_locked) goto clear_pmdnuma; } /* Migration could have started since the pmd_trans_migrating check */ if (!page_locked) { page_nid = -1; if (!get_page_unless_zero(page)) goto out_unlock; spin_unlock(fe->ptl); wait_on_page_locked(page); put_page(page); goto out; } /* * Page is misplaced. Page lock serialises migrations. Acquire anon_vma * to serialises splits */ get_page(page); spin_unlock(fe->ptl); anon_vma = page_lock_anon_vma_read(page); /* Confirm the PMD did not change while page_table_lock was released */ spin_lock(fe->ptl); if (unlikely(!pmd_same(pmd, *fe->pmd))) { unlock_page(page); put_page(page); page_nid = -1; goto out_unlock; } /* Bail if we fail to protect against THP splits for any reason */ if (unlikely(!anon_vma)) { put_page(page); page_nid = -1; goto clear_pmdnuma; } /* * Migrate the THP to the requested node, returns with page unlocked * and access rights restored. */ spin_unlock(fe->ptl); migrated = migrate_misplaced_transhuge_page(vma->vm_mm, vma, fe->pmd, pmd, fe->address, page, target_nid); if (migrated) { flags |= TNF_MIGRATED; page_nid = target_nid; } else flags |= TNF_MIGRATE_FAIL; goto out; clear_pmdnuma: BUG_ON(!PageLocked(page)); was_writable = pmd_write(pmd); pmd = pmd_modify(pmd, vma->vm_page_prot); pmd = pmd_mkyoung(pmd); if (was_writable) pmd = pmd_mkwrite(pmd); set_pmd_at(vma->vm_mm, haddr, fe->pmd, pmd); update_mmu_cache_pmd(vma, fe->address, fe->pmd); unlock_page(page); out_unlock: spin_unlock(fe->ptl); out: if (anon_vma) page_unlock_anon_vma_read(anon_vma); if (page_nid != -1) task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR, fe->flags); return 0; } /* * Return true if we do MADV_FREE successfully on entire pmd page. * Otherwise, return false. */ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, pmd_t *pmd, unsigned long addr, unsigned long next) { spinlock_t *ptl; pmd_t orig_pmd; struct page *page; struct mm_struct *mm = tlb->mm; bool ret = false; ptl = pmd_trans_huge_lock(pmd, vma); if (!ptl) goto out_unlocked; orig_pmd = *pmd; if (is_huge_zero_pmd(orig_pmd)) goto out; page = pmd_page(orig_pmd); /* * If other processes are mapping this page, we couldn't discard * the page unless they all do MADV_FREE so let's skip the page. */ if (page_mapcount(page) != 1) goto out; if (!trylock_page(page)) goto out; /* * If user want to discard part-pages of THP, split it so MADV_FREE * will deactivate only them. */ if (next - addr != HPAGE_PMD_SIZE) { get_page(page); spin_unlock(ptl); split_huge_page(page); unlock_page(page); put_page(page); goto out_unlocked; } if (PageDirty(page)) ClearPageDirty(page); unlock_page(page); if (PageActive(page)) deactivate_page(page); if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) { pmdp_invalidate(vma, addr, pmd); orig_pmd = pmd_mkold(orig_pmd); orig_pmd = pmd_mkclean(orig_pmd); set_pmd_at(mm, addr, pmd, orig_pmd); tlb_remove_pmd_tlb_entry(tlb, pmd, addr); } ret = true; out: spin_unlock(ptl); out_unlocked: return ret; } int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, pmd_t *pmd, unsigned long addr) { pmd_t orig_pmd; spinlock_t *ptl; ptl = __pmd_trans_huge_lock(pmd, vma); if (!ptl) return 0; /* * For architectures like ppc64 we look at deposited pgtable * when calling pmdp_huge_get_and_clear. So do the * pgtable_trans_huge_withdraw after finishing pmdp related * operations. */ orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd, tlb->fullmm); tlb_remove_pmd_tlb_entry(tlb, pmd, addr); if (vma_is_dax(vma)) { spin_unlock(ptl); if (is_huge_zero_pmd(orig_pmd)) tlb_remove_page(tlb, pmd_page(orig_pmd)); } else if (is_huge_zero_pmd(orig_pmd)) { pte_free(tlb->mm, pgtable_trans_huge_withdraw(tlb->mm, pmd)); atomic_long_dec(&tlb->mm->nr_ptes); spin_unlock(ptl); tlb_remove_page(tlb, pmd_page(orig_pmd)); } else { struct page *page = pmd_page(orig_pmd); page_remove_rmap(page, true); VM_BUG_ON_PAGE(page_mapcount(page) < 0, page); VM_BUG_ON_PAGE(!PageHead(page), page); if (PageAnon(page)) { pgtable_t pgtable; pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd); pte_free(tlb->mm, pgtable); atomic_long_dec(&tlb->mm->nr_ptes); add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR); } else { add_mm_counter(tlb->mm, MM_FILEPAGES, -HPAGE_PMD_NR); } spin_unlock(ptl); tlb_remove_page_size(tlb, page, HPAGE_PMD_SIZE); } return 1; } bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr, unsigned long new_addr, unsigned long old_end, pmd_t *old_pmd, pmd_t *new_pmd) { spinlock_t *old_ptl, *new_ptl; pmd_t pmd; struct mm_struct *mm = vma->vm_mm; bool force_flush = false; if ((old_addr & ~HPAGE_PMD_MASK) || (new_addr & ~HPAGE_PMD_MASK) || old_end - old_addr < HPAGE_PMD_SIZE) return false; /* * The destination pmd shouldn't be established, free_pgtables() * should have release it. */ if (WARN_ON(!pmd_none(*new_pmd))) { VM_BUG_ON(pmd_trans_huge(*new_pmd)); return false; } /* * We don't have to worry about the ordering of src and dst * ptlocks because exclusive mmap_sem prevents deadlock. */ old_ptl = __pmd_trans_huge_lock(old_pmd, vma); if (old_ptl) { new_ptl = pmd_lockptr(mm, new_pmd); if (new_ptl != old_ptl) spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING); pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd); if (pmd_present(pmd)) force_flush = true; VM_BUG_ON(!pmd_none(*new_pmd)); if (pmd_move_must_withdraw(new_ptl, old_ptl) && vma_is_anonymous(vma)) { pgtable_t pgtable; pgtable = pgtable_trans_huge_withdraw(mm, old_pmd); pgtable_trans_huge_deposit(mm, new_pmd, pgtable); } set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd)); if (force_flush) flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE); if (new_ptl != old_ptl) spin_unlock(new_ptl); spin_unlock(old_ptl); return true; } return false; } /* * Returns * - 0 if PMD could not be locked * - 1 if PMD was locked but protections unchange and TLB flush unnecessary * - HPAGE_PMD_NR is protections changed and TLB flush necessary */ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, unsigned long addr, pgprot_t newprot, int prot_numa) { struct mm_struct *mm = vma->vm_mm; spinlock_t *ptl; pmd_t entry; bool preserve_write; int ret; ptl = __pmd_trans_huge_lock(pmd, vma); if (!ptl) return 0; preserve_write = prot_numa && pmd_write(*pmd); ret = 1; /* * Avoid trapping faults against the zero page. The read-only * data is likely to be read-cached on the local CPU and * local/remote hits to the zero page are not interesting. */ if (prot_numa && is_huge_zero_pmd(*pmd)) goto unlock; if (prot_numa && pmd_protnone(*pmd)) goto unlock; /* * In case prot_numa, we are under down_read(mmap_sem). It's critical * to not clear pmd intermittently to avoid race with MADV_DONTNEED * which is also under down_read(mmap_sem): * * CPU0: CPU1: * change_huge_pmd(prot_numa=1) * pmdp_huge_get_and_clear_notify() * madvise_dontneed() * zap_pmd_range() * pmd_trans_huge(*pmd) == 0 (without ptl) * // skip the pmd * set_pmd_at(); * // pmd is re-established * * The race makes MADV_DONTNEED miss the huge pmd and don't clear it * which may break userspace. * * pmdp_invalidate() is required to make sure we don't miss * dirty/young flags set by hardware. */ entry = *pmd; pmdp_invalidate(vma, addr, pmd); /* * Recover dirty/young flags. It relies on pmdp_invalidate to not * corrupt them. */ if (pmd_dirty(*pmd)) entry = pmd_mkdirty(entry); if (pmd_young(*pmd)) entry = pmd_mkyoung(entry); entry = pmd_modify(entry, newprot); if (preserve_write) entry = pmd_mkwrite(entry); ret = HPAGE_PMD_NR; set_pmd_at(mm, addr, pmd, entry); BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry)); unlock: spin_unlock(ptl); return ret; } /* * Returns page table lock pointer if a given pmd maps a thp, NULL otherwise. * * Note that if it returns page table lock pointer, this routine returns without * unlocking page table lock. So callers must unlock it. */ spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma) { spinlock_t *ptl; ptl = pmd_lock(vma->vm_mm, pmd); if (likely(pmd_trans_huge(*pmd) || pmd_devmap(*pmd))) return ptl; spin_unlock(ptl); return NULL; } static void __split_huge_zero_page_pmd(struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd) { struct mm_struct *mm = vma->vm_mm; pgtable_t pgtable; pmd_t _pmd; int i; /* leave pmd empty until pte is filled */ pmdp_huge_clear_flush_notify(vma, haddr, pmd); pgtable = pgtable_trans_huge_withdraw(mm, pmd); pmd_populate(mm, &_pmd, pgtable); for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) { pte_t *pte, entry; entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot); entry = pte_mkspecial(entry); pte = pte_offset_map(&_pmd, haddr); VM_BUG_ON(!pte_none(*pte)); set_pte_at(mm, haddr, pte, entry); pte_unmap(pte); } smp_wmb(); /* make pte visible before pmd */ pmd_populate(mm, pmd, pgtable); } static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, unsigned long haddr, bool freeze) { struct mm_struct *mm = vma->vm_mm; struct page *page; pgtable_t pgtable; pmd_t _pmd; bool young, write, dirty, soft_dirty; unsigned long addr; int i; VM_BUG_ON(haddr & ~HPAGE_PMD_MASK); VM_BUG_ON_VMA(vma->vm_start > haddr, vma); VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma); VM_BUG_ON(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)); count_vm_event(THP_SPLIT_PMD); if (!vma_is_anonymous(vma)) { _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd); if (vma_is_dax(vma)) return; page = pmd_page(_pmd); if (!PageDirty(page) && pmd_dirty(_pmd)) set_page_dirty(page); if (!PageReferenced(page) && pmd_young(_pmd)) SetPageReferenced(page); page_remove_rmap(page, true); put_page(page); add_mm_counter(mm, MM_FILEPAGES, -HPAGE_PMD_NR); return; } else if (is_huge_zero_pmd(*pmd)) { return __split_huge_zero_page_pmd(vma, haddr, pmd); } page = pmd_page(*pmd); VM_BUG_ON_PAGE(!page_count(page), page); page_ref_add(page, HPAGE_PMD_NR - 1); write = pmd_write(*pmd); young = pmd_young(*pmd); dirty = pmd_dirty(*pmd); soft_dirty = pmd_soft_dirty(*pmd); pmdp_huge_split_prepare(vma, haddr, pmd); pgtable = pgtable_trans_huge_withdraw(mm, pmd); pmd_populate(mm, &_pmd, pgtable); for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) { pte_t entry, *pte; /* * Note that NUMA hinting access restrictions are not * transferred to avoid any possibility of altering * permissions across VMAs. */ if (freeze) { swp_entry_t swp_entry; swp_entry = make_migration_entry(page + i, write); entry = swp_entry_to_pte(swp_entry); if (soft_dirty) entry = pte_swp_mksoft_dirty(entry); } else { entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot)); entry = maybe_mkwrite(entry, vma); if (!write) entry = pte_wrprotect(entry); if (!young) entry = pte_mkold(entry); if (soft_dirty) entry = pte_mksoft_dirty(entry); } if (dirty) SetPageDirty(page + i); pte = pte_offset_map(&_pmd, addr); BUG_ON(!pte_none(*pte)); set_pte_at(mm, addr, pte, entry); atomic_inc(&page[i]._mapcount); pte_unmap(pte); } /* * Set PG_double_map before dropping compound_mapcount to avoid * false-negative page_mapped(). */ if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) { for (i = 0; i < HPAGE_PMD_NR; i++) atomic_inc(&page[i]._mapcount); } if (atomic_add_negative(-1, compound_mapcount_ptr(page))) { /* Last compound_mapcount is gone. */ __dec_node_page_state(page, NR_ANON_THPS); if (TestClearPageDoubleMap(page)) { /* No need in mapcount reference anymore */ for (i = 0; i < HPAGE_PMD_NR; i++) atomic_dec(&page[i]._mapcount); } } smp_wmb(); /* make pte visible before pmd */ /* * Up to this point the pmd is present and huge and userland has the * whole access to the hugepage during the split (which happens in * place). If we overwrite the pmd with the not-huge version pointing * to the pte here (which of course we could if all CPUs were bug * free), userland could trigger a small page size TLB miss on the * small sized TLB while the hugepage TLB entry is still established in * the huge TLB. Some CPU doesn't like that. * See http://support.amd.com/us/Processor_TechDocs/41322.pdf, Erratum * 383 on page 93. Intel should be safe but is also warns that it's * only safe if the permission and cache attributes of the two entries * loaded in the two TLB is identical (which should be the case here). * But it is generally safer to never allow small and huge TLB entries * for the same virtual address to be loaded simultaneously. So instead * of doing "pmd_populate(); flush_pmd_tlb_range();" we first mark the * current pmd notpresent (atomically because here the pmd_trans_huge * and pmd_trans_splitting must remain set at all times on the pmd * until the split is complete for this pmd), then we flush the SMP TLB * and finally we write the non-huge version of the pmd entry with * pmd_populate. */ pmdp_invalidate(vma, haddr, pmd); pmd_populate(mm, pmd, pgtable); if (freeze) { for (i = 0; i < HPAGE_PMD_NR; i++) { page_remove_rmap(page + i, false); put_page(page + i); } } } void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, unsigned long address, bool freeze, struct page *page) { spinlock_t *ptl; struct mm_struct *mm = vma->vm_mm; unsigned long haddr = address & HPAGE_PMD_MASK; bool was_locked = false; pmd_t _pmd; mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE); ptl = pmd_lock(mm, pmd); /* * If caller asks to setup a migration entries, we need a page to check * pmd against. Otherwise we can end up replacing wrong page. */ VM_BUG_ON(freeze && !page); if (page) { VM_WARN_ON_ONCE(!PageLocked(page)); was_locked = true; if (page != pmd_page(*pmd)) goto out; } repeat: if (pmd_trans_huge(*pmd)) { if (!page) { page = pmd_page(*pmd); if (unlikely(!trylock_page(page))) { get_page(page); _pmd = *pmd; spin_unlock(ptl); lock_page(page); spin_lock(ptl); if (unlikely(!pmd_same(*pmd, _pmd))) { unlock_page(page); put_page(page); page = NULL; goto repeat; } put_page(page); } } if (PageMlocked(page)) clear_page_mlock(page); } else if (!pmd_devmap(*pmd)) goto out; __split_huge_pmd_locked(vma, pmd, haddr, freeze); out: spin_unlock(ptl); if (!was_locked && page) unlock_page(page); mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE); } void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, bool freeze, struct page *page) { pgd_t *pgd; pud_t *pud; pmd_t *pmd; pgd = pgd_offset(vma->vm_mm, address); if (!pgd_present(*pgd)) return; pud = pud_offset(pgd, address); if (!pud_present(*pud)) return; pmd = pmd_offset(pud, address); __split_huge_pmd(vma, pmd, address, freeze, page); } void vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long start, unsigned long end, long adjust_next) { /* * If the new start address isn't hpage aligned and it could * previously contain an hugepage: check if we need to split * an huge pmd. */ if (start & ~HPAGE_PMD_MASK && (start & HPAGE_PMD_MASK) >= vma->vm_start && (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end) split_huge_pmd_address(vma, start, false, NULL); /* * If the new end address isn't hpage aligned and it could * previously contain an hugepage: check if we need to split * an huge pmd. */ if (end & ~HPAGE_PMD_MASK && (end & HPAGE_PMD_MASK) >= vma->vm_start && (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end) split_huge_pmd_address(vma, end, false, NULL); /* * If we're also updating the vma->vm_next->vm_start, if the new * vm_next->vm_start isn't page aligned and it could previously * contain an hugepage: check if we need to split an huge pmd. */ if (adjust_next > 0) { struct vm_area_struct *next = vma->vm_next; unsigned long nstart = next->vm_start; nstart += adjust_next << PAGE_SHIFT; if (nstart & ~HPAGE_PMD_MASK && (nstart & HPAGE_PMD_MASK) >= next->vm_start && (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end) split_huge_pmd_address(next, nstart, false, NULL); } } static void unmap_page(struct page *page) { enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS | TTU_RMAP_LOCKED; int i, ret; VM_BUG_ON_PAGE(!PageHead(page), page); if (PageAnon(page)) ttu_flags |= TTU_MIGRATION; /* We only need TTU_SPLIT_HUGE_PMD once */ ret = try_to_unmap(page, ttu_flags | TTU_SPLIT_HUGE_PMD); for (i = 1; !ret && i < HPAGE_PMD_NR; i++) { /* Cut short if the page is unmapped */ if (page_count(page) == 1) return; ret = try_to_unmap(page + i, ttu_flags); } VM_BUG_ON_PAGE(ret, page + i - 1); } static void remap_page(struct page *page) { int i; for (i = 0; i < HPAGE_PMD_NR; i++) remove_migration_ptes(page + i, page + i, true); } static void __split_huge_page_tail(struct page *head, int tail, struct lruvec *lruvec, struct list_head *list) { struct page *page_tail = head + tail; VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail); /* * Clone page flags before unfreezing refcount. * * After successful get_page_unless_zero() might follow flags change, * for exmaple lock_page() which set PG_waiters. */ page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP; page_tail->flags |= (head->flags & ((1L << PG_referenced) | (1L << PG_swapbacked) | (1L << PG_mlocked) | (1L << PG_uptodate) | (1L << PG_active) | (1L << PG_locked) | (1L << PG_unevictable) | (1L << PG_dirty))); /* ->mapping in first tail page is compound_mapcount */ VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING, page_tail); page_tail->mapping = head->mapping; page_tail->index = head->index + tail; /* Page flags must be visible before we make the page non-compound. */ smp_wmb(); /* * Clear PageTail before unfreezing page refcount. * * After successful get_page_unless_zero() might follow put_page() * which needs correct compound_head(). */ clear_compound_head(page_tail); /* Finally unfreeze refcount. Additional reference from page cache. */ page_ref_unfreeze(page_tail, 1 + (!PageAnon(head) || PageSwapCache(head))); if (page_is_young(head)) set_page_young(page_tail); if (page_is_idle(head)) set_page_idle(page_tail); page_cpupid_xchg_last(page_tail, page_cpupid_last(head)); lru_add_page_tail(head, page_tail, lruvec, list); } static void __split_huge_page(struct page *page, struct list_head *list, pgoff_t end, unsigned long flags) { struct page *head = compound_head(page); struct zone *zone = page_zone(head); struct lruvec *lruvec; int i; lruvec = mem_cgroup_page_lruvec(head, zone->zone_pgdat); /* complete memcg works before add pages to LRU */ mem_cgroup_split_huge_fixup(head); for (i = HPAGE_PMD_NR - 1; i >= 1; i--) { __split_huge_page_tail(head, i, lruvec, list); /* Some pages can be beyond i_size: drop them from page cache */ if (head[i].index >= end) { __ClearPageDirty(head + i); __delete_from_page_cache(head + i, NULL); if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head)) shmem_uncharge(head->mapping->host, 1); put_page(head + i); } } ClearPageCompound(head); split_page_owner(head, HPAGE_PMD_ORDER); /* See comment in __split_huge_page_tail() */ if (PageAnon(head)) { page_ref_inc(head); } else { /* Additional pin to radix tree */ page_ref_add(head, 2); spin_unlock(&head->mapping->tree_lock); } spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags); remap_page(head); for (i = 0; i < HPAGE_PMD_NR; i++) { struct page *subpage = head + i; if (subpage == page) continue; unlock_page(subpage); /* * Subpages may be freed if there wasn't any mapping * like if add_to_swap() is running on a lru page that * had its mapping zapped. And freeing these pages * requires taking the lru_lock so we do the put_page * of the tail pages after the split is complete. */ put_page(subpage); } } int total_mapcount(struct page *page) { int i, compound, ret; VM_BUG_ON_PAGE(PageTail(page), page); if (likely(!PageCompound(page))) return atomic_read(&page->_mapcount) + 1; compound = compound_mapcount(page); if (PageHuge(page)) return compound; ret = compound; for (i = 0; i < HPAGE_PMD_NR; i++) ret += atomic_read(&page[i]._mapcount) + 1; /* File pages has compound_mapcount included in _mapcount */ if (!PageAnon(page)) return ret - compound * HPAGE_PMD_NR; if (PageDoubleMap(page)) ret -= HPAGE_PMD_NR; return ret; } /* * This calculates accurately how many mappings a transparent hugepage * has (unlike page_mapcount() which isn't fully accurate). This full * accuracy is primarily needed to know if copy-on-write faults can * reuse the page and change the mapping to read-write instead of * copying them. At the same time this returns the total_mapcount too. * * The function returns the highest mapcount any one of the subpages * has. If the return value is one, even if different processes are * mapping different subpages of the transparent hugepage, they can * all reuse it, because each process is reusing a different subpage. * * The total_mapcount is instead counting all virtual mappings of the * subpages. If the total_mapcount is equal to "one", it tells the * caller all mappings belong to the same "mm" and in turn the * anon_vma of the transparent hugepage can become the vma->anon_vma * local one as no other process may be mapping any of the subpages. * * It would be more accurate to replace page_mapcount() with * page_trans_huge_mapcount(), however we only use * page_trans_huge_mapcount() in the copy-on-write faults where we * need full accuracy to avoid breaking page pinning, because * page_trans_huge_mapcount() is slower than page_mapcount(). */ int page_trans_huge_mapcount(struct page *page, int *total_mapcount) { int i, ret, _total_mapcount, mapcount; /* hugetlbfs shouldn't call it */ VM_BUG_ON_PAGE(PageHuge(page), page); if (likely(!PageTransCompound(page))) { mapcount = atomic_read(&page->_mapcount) + 1; if (total_mapcount) *total_mapcount = mapcount; return mapcount; } page = compound_head(page); _total_mapcount = ret = 0; for (i = 0; i < HPAGE_PMD_NR; i++) { mapcount = atomic_read(&page[i]._mapcount) + 1; ret = max(ret, mapcount); _total_mapcount += mapcount; } if (PageDoubleMap(page)) { ret -= 1; _total_mapcount -= HPAGE_PMD_NR; } mapcount = compound_mapcount(page); ret += mapcount; _total_mapcount += mapcount; if (total_mapcount) *total_mapcount = _total_mapcount; return ret; } /* * This function splits huge page into normal pages. @page can point to any * subpage of huge page to split. Split doesn't change the position of @page. * * Only caller must hold pin on the @page, otherwise split fails with -EBUSY. * The huge page must be locked. * * If @list is null, tail pages will be added to LRU list, otherwise, to @list. * * Both head page and tail pages will inherit mapping, flags, and so on from * the hugepage. * * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if * they are not mapped. * * Returns 0 if the hugepage is split successfully. * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under * us. */ int split_huge_page_to_list(struct page *page, struct list_head *list) { struct page *head = compound_head(page); struct pglist_data *pgdata = NODE_DATA(page_to_nid(head)); struct anon_vma *anon_vma = NULL; struct address_space *mapping = NULL; int count, mapcount, extra_pins, ret; bool mlocked; unsigned long flags; pgoff_t end; VM_BUG_ON_PAGE(is_huge_zero_page(head), head); VM_BUG_ON_PAGE(!PageLocked(page), page); VM_BUG_ON_PAGE(!PageSwapBacked(page), page); VM_BUG_ON_PAGE(!PageCompound(page), page); if (PageAnon(head)) { /* * The caller does not necessarily hold an mmap_sem that would * prevent the anon_vma disappearing so we first we take a * reference to it and then lock the anon_vma for write. This * is similar to page_lock_anon_vma_read except the write lock * is taken to serialise against parallel split or collapse * operations. */ anon_vma = page_get_anon_vma(head); if (!anon_vma) { ret = -EBUSY; goto out; } extra_pins = 0; end = -1; mapping = NULL; anon_vma_lock_write(anon_vma); } else { mapping = head->mapping; /* Truncated ? */ if (!mapping) { ret = -EBUSY; goto out; } /* Addidional pins from radix tree */ extra_pins = HPAGE_PMD_NR; anon_vma = NULL; i_mmap_lock_read(mapping); /* *__split_huge_page() may need to trim off pages beyond EOF: * but on 32-bit, i_size_read() takes an irq-unsafe seqlock, * which cannot be nested inside the page tree lock. So note * end now: i_size itself may be changed at any moment, but * head page lock is good enough to serialize the trimming. */ end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE); } /* * Racy check if we can split the page, before unmap_page() will * split PMDs */ if (total_mapcount(head) != page_count(head) - extra_pins - 1) { ret = -EBUSY; goto out_unlock; } mlocked = PageMlocked(page); unmap_page(head); VM_BUG_ON_PAGE(compound_mapcount(head), head); /* Make sure the page is not on per-CPU pagevec as it takes pin */ if (mlocked) lru_add_drain(); /* prevent PageLRU to go away from under us, and freeze lru stats */ spin_lock_irqsave(zone_lru_lock(page_zone(head)), flags); if (mapping) { void **pslot; spin_lock(&mapping->tree_lock); pslot = radix_tree_lookup_slot(&mapping->page_tree, page_index(head)); /* * Check if the head page is present in radix tree. * We assume all tail are present too, if head is there. */ if (radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != head) goto fail; } /* Prevent deferred_split_scan() touching ->_refcount */ spin_lock(&pgdata->split_queue_lock); count = page_count(head); mapcount = total_mapcount(head); if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) { if (!list_empty(page_deferred_list(head))) { pgdata->split_queue_len--; list_del(page_deferred_list(head)); } if (mapping) __dec_node_page_state(page, NR_SHMEM_THPS); spin_unlock(&pgdata->split_queue_lock); __split_huge_page(page, list, end, flags); ret = 0; } else { if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) { pr_alert("total_mapcount: %u, page_count(): %u\n", mapcount, count); if (PageTail(page)) dump_page(head, NULL); dump_page(page, "total_mapcount(head) > 0"); BUG(); } spin_unlock(&pgdata->split_queue_lock); fail: if (mapping) spin_unlock(&mapping->tree_lock); spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags); remap_page(head); ret = -EBUSY; } out_unlock: if (anon_vma) { anon_vma_unlock_write(anon_vma); put_anon_vma(anon_vma); } if (mapping) i_mmap_unlock_read(mapping); out: count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED); return ret; } void free_transhuge_page(struct page *page) { struct pglist_data *pgdata = NODE_DATA(page_to_nid(page)); unsigned long flags; spin_lock_irqsave(&pgdata->split_queue_lock, flags); if (!list_empty(page_deferred_list(page))) { pgdata->split_queue_len--; list_del(page_deferred_list(page)); } spin_unlock_irqrestore(&pgdata->split_queue_lock, flags); free_compound_page(page); } void deferred_split_huge_page(struct page *page) { struct pglist_data *pgdata = NODE_DATA(page_to_nid(page)); unsigned long flags; VM_BUG_ON_PAGE(!PageTransHuge(page), page); spin_lock_irqsave(&pgdata->split_queue_lock, flags); if (list_empty(page_deferred_list(page))) { count_vm_event(THP_DEFERRED_SPLIT_PAGE); list_add_tail(page_deferred_list(page), &pgdata->split_queue); pgdata->split_queue_len++; } spin_unlock_irqrestore(&pgdata->split_queue_lock, flags); } static unsigned long deferred_split_count(struct shrinker *shrink, struct shrink_control *sc) { struct pglist_data *pgdata = NODE_DATA(sc->nid); return ACCESS_ONCE(pgdata->split_queue_len); } static unsigned long deferred_split_scan(struct shrinker *shrink, struct shrink_control *sc) { struct pglist_data *pgdata = NODE_DATA(sc->nid); unsigned long flags; LIST_HEAD(list), *pos, *next; struct page *page; int split = 0; spin_lock_irqsave(&pgdata->split_queue_lock, flags); /* Take pin on all head pages to avoid freeing them under us */ list_for_each_safe(pos, next, &pgdata->split_queue) { page = list_entry((void *)pos, struct page, mapping); page = compound_head(page); if (get_page_unless_zero(page)) { list_move(page_deferred_list(page), &list); } else { /* We lost race with put_compound_page() */ list_del_init(page_deferred_list(page)); pgdata->split_queue_len--; } if (!--sc->nr_to_scan) break; } spin_unlock_irqrestore(&pgdata->split_queue_lock, flags); list_for_each_safe(pos, next, &list) { page = list_entry((void *)pos, struct page, mapping); if (!trylock_page(page)) goto next; /* split_huge_page() removes page from list on success */ if (!split_huge_page(page)) split++; unlock_page(page); next: put_page(page); } spin_lock_irqsave(&pgdata->split_queue_lock, flags); list_splice_tail(&list, &pgdata->split_queue); spin_unlock_irqrestore(&pgdata->split_queue_lock, flags); /* * Stop shrinker if we didn't split any page, but the queue is empty. * This can happen if pages were freed under us. */ if (!split && list_empty(&pgdata->split_queue)) return SHRINK_STOP; return split; } static struct shrinker deferred_split_shrinker = { .count_objects = deferred_split_count, .scan_objects = deferred_split_scan, .seeks = DEFAULT_SEEKS, .flags = SHRINKER_NUMA_AWARE, }; #ifdef CONFIG_DEBUG_FS static int split_huge_pages_set(void *data, u64 val) { struct zone *zone; struct page *page; unsigned long pfn, max_zone_pfn; unsigned long total = 0, split = 0; if (val != 1) return -EINVAL; for_each_populated_zone(zone) { max_zone_pfn = zone_end_pfn(zone); for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) { if (!pfn_valid(pfn)) continue; page = pfn_to_page(pfn); if (!get_page_unless_zero(page)) continue; if (zone != page_zone(page)) goto next; if (!PageHead(page) || PageHuge(page) || !PageLRU(page)) goto next; total++; lock_page(page); if (!split_huge_page(page)) split++; unlock_page(page); next: put_page(page); } } pr_info("%lu of %lu THP split\n", split, total); return 0; } DEFINE_SIMPLE_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set, "%llu\n"); static int __init split_huge_pages_debugfs(void) { void *ret; ret = debugfs_create_file("split_huge_pages", 0200, NULL, NULL, &split_huge_pages_fops); if (!ret) pr_warn("Failed to create split_huge_pages in debugfs"); return 0; } late_initcall(split_huge_pages_debugfs); #endif