diff options
Diffstat (limited to 'mm/khugepaged.c')
| -rw-r--r-- | mm/khugepaged.c | 2738 |
1 files changed, 2738 insertions, 0 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c new file mode 100644 index 000000000..65bd0b105 --- /dev/null +++ b/mm/khugepaged.c @@ -0,0 +1,2738 @@ +// SPDX-License-Identifier: GPL-2.0 +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/mm.h> +#include <linux/sched.h> +#include <linux/sched/mm.h> +#include <linux/sched/coredump.h> +#include <linux/mmu_notifier.h> +#include <linux/rmap.h> +#include <linux/swap.h> +#include <linux/mm_inline.h> +#include <linux/kthread.h> +#include <linux/khugepaged.h> +#include <linux/freezer.h> +#include <linux/mman.h> +#include <linux/hashtable.h> +#include <linux/userfaultfd_k.h> +#include <linux/page_idle.h> +#include <linux/page_table_check.h> +#include <linux/swapops.h> +#include <linux/shmem_fs.h> + +#include <asm/tlb.h> +#include <asm/pgalloc.h> +#include "internal.h" +#include "mm_slot.h" + +enum scan_result { + SCAN_FAIL, + SCAN_SUCCEED, + SCAN_PMD_NULL, + SCAN_PMD_NONE, + SCAN_PMD_MAPPED, + SCAN_EXCEED_NONE_PTE, + SCAN_EXCEED_SWAP_PTE, + SCAN_EXCEED_SHARED_PTE, + SCAN_PTE_NON_PRESENT, + SCAN_PTE_UFFD_WP, + SCAN_PTE_MAPPED_HUGEPAGE, + SCAN_PAGE_RO, + SCAN_LACK_REFERENCED_PAGE, + SCAN_PAGE_NULL, + SCAN_SCAN_ABORT, + SCAN_PAGE_COUNT, + SCAN_PAGE_LRU, + SCAN_PAGE_LOCK, + SCAN_PAGE_ANON, + SCAN_PAGE_COMPOUND, + SCAN_ANY_PROCESS, + SCAN_VMA_NULL, + SCAN_VMA_CHECK, + SCAN_ADDRESS_RANGE, + SCAN_DEL_PAGE_LRU, + SCAN_ALLOC_HUGE_PAGE_FAIL, + SCAN_CGROUP_CHARGE_FAIL, + SCAN_TRUNCATED, + SCAN_PAGE_HAS_PRIVATE, +}; + +#define CREATE_TRACE_POINTS +#include <trace/events/huge_memory.h> + +static struct task_struct *khugepaged_thread __read_mostly; +static DEFINE_MUTEX(khugepaged_mutex); + +/* default scan 8*512 pte (or vmas) every 30 second */ +static unsigned int khugepaged_pages_to_scan __read_mostly; +static unsigned int khugepaged_pages_collapsed; +static unsigned int khugepaged_full_scans; +static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000; +/* during fragmentation poll the hugepage allocator once every minute */ +static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000; +static unsigned long khugepaged_sleep_expire; +static DEFINE_SPINLOCK(khugepaged_mm_lock); +static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait); +/* + * default collapse hugepages if there is at least one pte mapped like + * it would have happened if the vma was large enough during page + * fault. + * + * Note that these are only respected if collapse was initiated by khugepaged. + */ +static unsigned int khugepaged_max_ptes_none __read_mostly; +static unsigned int khugepaged_max_ptes_swap __read_mostly; +static unsigned int khugepaged_max_ptes_shared __read_mostly; + +#define MM_SLOTS_HASH_BITS 10 +static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS); + +static struct kmem_cache *mm_slot_cache __read_mostly; + +#define MAX_PTE_MAPPED_THP 8 + +struct collapse_control { + bool is_khugepaged; + + /* Num pages scanned per node */ + u32 node_load[MAX_NUMNODES]; + + /* nodemask for allocation fallback */ + nodemask_t alloc_nmask; +}; + +/** + * struct khugepaged_mm_slot - khugepaged information per mm that is being scanned + * @slot: hash lookup from mm to mm_slot + * @nr_pte_mapped_thp: number of pte mapped THP + * @pte_mapped_thp: address array corresponding pte mapped THP + */ +struct khugepaged_mm_slot { + struct mm_slot slot; + + /* pte-mapped THP in this mm */ + int nr_pte_mapped_thp; + unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP]; +}; + +/** + * struct khugepaged_scan - cursor for scanning + * @mm_head: the head of the mm list to scan + * @mm_slot: the current mm_slot we are scanning + * @address: the next address inside that to be scanned + * + * There is only the one khugepaged_scan instance of this cursor structure. + */ +struct khugepaged_scan { + struct list_head mm_head; + struct khugepaged_mm_slot *mm_slot; + unsigned long address; +}; + +static struct khugepaged_scan khugepaged_scan = { + .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head), +}; + +#ifdef CONFIG_SYSFS +static ssize_t scan_sleep_millisecs_show(struct kobject *kobj, + struct kobj_attribute *attr, + char *buf) +{ + return sysfs_emit(buf, "%u\n", khugepaged_scan_sleep_millisecs); +} + +static ssize_t scan_sleep_millisecs_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + unsigned int msecs; + int err; + + err = kstrtouint(buf, 10, &msecs); + if (err) + return -EINVAL; + + khugepaged_scan_sleep_millisecs = msecs; + khugepaged_sleep_expire = 0; + wake_up_interruptible(&khugepaged_wait); + + return count; +} +static struct kobj_attribute scan_sleep_millisecs_attr = + __ATTR_RW(scan_sleep_millisecs); + +static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj, + struct kobj_attribute *attr, + char *buf) +{ + return sysfs_emit(buf, "%u\n", khugepaged_alloc_sleep_millisecs); +} + +static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + unsigned int msecs; + int err; + + err = kstrtouint(buf, 10, &msecs); + if (err) + return -EINVAL; + + khugepaged_alloc_sleep_millisecs = msecs; + khugepaged_sleep_expire = 0; + wake_up_interruptible(&khugepaged_wait); + + return count; +} +static struct kobj_attribute alloc_sleep_millisecs_attr = + __ATTR_RW(alloc_sleep_millisecs); + +static ssize_t pages_to_scan_show(struct kobject *kobj, + struct kobj_attribute *attr, + char *buf) +{ + return sysfs_emit(buf, "%u\n", khugepaged_pages_to_scan); +} +static ssize_t pages_to_scan_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + unsigned int pages; + int err; + + err = kstrtouint(buf, 10, &pages); + if (err || !pages) + return -EINVAL; + + khugepaged_pages_to_scan = pages; + + return count; +} +static struct kobj_attribute pages_to_scan_attr = + __ATTR_RW(pages_to_scan); + +static ssize_t pages_collapsed_show(struct kobject *kobj, + struct kobj_attribute *attr, + char *buf) +{ + return sysfs_emit(buf, "%u\n", khugepaged_pages_collapsed); +} +static struct kobj_attribute pages_collapsed_attr = + __ATTR_RO(pages_collapsed); + +static ssize_t full_scans_show(struct kobject *kobj, + struct kobj_attribute *attr, + char *buf) +{ + return sysfs_emit(buf, "%u\n", khugepaged_full_scans); +} +static struct kobj_attribute full_scans_attr = + __ATTR_RO(full_scans); + +static ssize_t defrag_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return single_hugepage_flag_show(kobj, attr, buf, + TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG); +} +static ssize_t defrag_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_DEFRAG_KHUGEPAGED_FLAG); +} +static struct kobj_attribute khugepaged_defrag_attr = + __ATTR_RW(defrag); + +/* + * max_ptes_none controls if khugepaged should collapse hugepages over + * any unmapped ptes in turn potentially increasing the memory + * footprint of the vmas. When max_ptes_none is 0 khugepaged will not + * reduce the available free memory in the system as it + * runs. Increasing max_ptes_none will instead potentially reduce the + * free memory in the system during the khugepaged scan. + */ +static ssize_t max_ptes_none_show(struct kobject *kobj, + struct kobj_attribute *attr, + char *buf) +{ + return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_none); +} +static ssize_t max_ptes_none_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + unsigned long max_ptes_none; + + err = kstrtoul(buf, 10, &max_ptes_none); + if (err || max_ptes_none > HPAGE_PMD_NR - 1) + return -EINVAL; + + khugepaged_max_ptes_none = max_ptes_none; + + return count; +} +static struct kobj_attribute khugepaged_max_ptes_none_attr = + __ATTR_RW(max_ptes_none); + +static ssize_t max_ptes_swap_show(struct kobject *kobj, + struct kobj_attribute *attr, + char *buf) +{ + return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_swap); +} + +static ssize_t max_ptes_swap_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + unsigned long max_ptes_swap; + + err = kstrtoul(buf, 10, &max_ptes_swap); + if (err || max_ptes_swap > HPAGE_PMD_NR - 1) + return -EINVAL; + + khugepaged_max_ptes_swap = max_ptes_swap; + + return count; +} + +static struct kobj_attribute khugepaged_max_ptes_swap_attr = + __ATTR_RW(max_ptes_swap); + +static ssize_t max_ptes_shared_show(struct kobject *kobj, + struct kobj_attribute *attr, + char *buf) +{ + return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_shared); +} + +static ssize_t max_ptes_shared_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + unsigned long max_ptes_shared; + + err = kstrtoul(buf, 10, &max_ptes_shared); + if (err || max_ptes_shared > HPAGE_PMD_NR - 1) + return -EINVAL; + + khugepaged_max_ptes_shared = max_ptes_shared; + + return count; +} + +static struct kobj_attribute khugepaged_max_ptes_shared_attr = + __ATTR_RW(max_ptes_shared); + +static struct attribute *khugepaged_attr[] = { + &khugepaged_defrag_attr.attr, + &khugepaged_max_ptes_none_attr.attr, + &khugepaged_max_ptes_swap_attr.attr, + &khugepaged_max_ptes_shared_attr.attr, + &pages_to_scan_attr.attr, + &pages_collapsed_attr.attr, + &full_scans_attr.attr, + &scan_sleep_millisecs_attr.attr, + &alloc_sleep_millisecs_attr.attr, + NULL, +}; + +struct attribute_group khugepaged_attr_group = { + .attrs = khugepaged_attr, + .name = "khugepaged", +}; +#endif /* CONFIG_SYSFS */ + +int hugepage_madvise(struct vm_area_struct *vma, + unsigned long *vm_flags, int advice) +{ + switch (advice) { + case MADV_HUGEPAGE: +#ifdef CONFIG_S390 + /* + * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390 + * can't handle this properly after s390_enable_sie, so we simply + * ignore the madvise to prevent qemu from causing a SIGSEGV. + */ + if (mm_has_pgste(vma->vm_mm)) + return 0; +#endif + *vm_flags &= ~VM_NOHUGEPAGE; + *vm_flags |= VM_HUGEPAGE; + /* + * If the vma become good for khugepaged to scan, + * register it here without waiting a page fault that + * may not happen any time soon. + */ + khugepaged_enter_vma(vma, *vm_flags); + break; + case MADV_NOHUGEPAGE: + *vm_flags &= ~VM_HUGEPAGE; + *vm_flags |= VM_NOHUGEPAGE; + /* + * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning + * this vma even if we leave the mm registered in khugepaged if + * it got registered before VM_NOHUGEPAGE was set. + */ + break; + } + + return 0; +} + +int __init khugepaged_init(void) +{ + mm_slot_cache = kmem_cache_create("khugepaged_mm_slot", + sizeof(struct khugepaged_mm_slot), + __alignof__(struct khugepaged_mm_slot), + 0, NULL); + if (!mm_slot_cache) + return -ENOMEM; + + khugepaged_pages_to_scan = HPAGE_PMD_NR * 8; + khugepaged_max_ptes_none = HPAGE_PMD_NR - 1; + khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8; + khugepaged_max_ptes_shared = HPAGE_PMD_NR / 2; + + return 0; +} + +void __init khugepaged_destroy(void) +{ + kmem_cache_destroy(mm_slot_cache); +} + +static inline int hpage_collapse_test_exit(struct mm_struct *mm) +{ + return atomic_read(&mm->mm_users) == 0; +} + +void __khugepaged_enter(struct mm_struct *mm) +{ + struct khugepaged_mm_slot *mm_slot; + struct mm_slot *slot; + int wakeup; + + mm_slot = mm_slot_alloc(mm_slot_cache); + if (!mm_slot) + return; + + slot = &mm_slot->slot; + + /* __khugepaged_exit() must not run from under us */ + VM_BUG_ON_MM(hpage_collapse_test_exit(mm), mm); + if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) { + mm_slot_free(mm_slot_cache, mm_slot); + return; + } + + spin_lock(&khugepaged_mm_lock); + mm_slot_insert(mm_slots_hash, mm, slot); + /* + * Insert just behind the scanning cursor, to let the area settle + * down a little. + */ + wakeup = list_empty(&khugepaged_scan.mm_head); + list_add_tail(&slot->mm_node, &khugepaged_scan.mm_head); + spin_unlock(&khugepaged_mm_lock); + + mmgrab(mm); + if (wakeup) + wake_up_interruptible(&khugepaged_wait); +} + +void khugepaged_enter_vma(struct vm_area_struct *vma, + unsigned long vm_flags) +{ + if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) && + hugepage_flags_enabled()) { + if (hugepage_vma_check(vma, vm_flags, false, false, true)) + __khugepaged_enter(vma->vm_mm); + } +} + +void __khugepaged_exit(struct mm_struct *mm) +{ + struct khugepaged_mm_slot *mm_slot; + struct mm_slot *slot; + int free = 0; + + spin_lock(&khugepaged_mm_lock); + slot = mm_slot_lookup(mm_slots_hash, mm); + mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot); + if (mm_slot && khugepaged_scan.mm_slot != mm_slot) { + hash_del(&slot->hash); + list_del(&slot->mm_node); + free = 1; + } + spin_unlock(&khugepaged_mm_lock); + + if (free) { + clear_bit(MMF_VM_HUGEPAGE, &mm->flags); + mm_slot_free(mm_slot_cache, mm_slot); + mmdrop(mm); + } else if (mm_slot) { + /* + * This is required to serialize against + * hpage_collapse_test_exit() (which is guaranteed to run + * under mmap sem read mode). Stop here (after we return all + * pagetables will be destroyed) until khugepaged has finished + * working on the pagetables under the mmap_lock. + */ + mmap_write_lock(mm); + mmap_write_unlock(mm); + } +} + +static void release_pte_page(struct page *page) +{ + mod_node_page_state(page_pgdat(page), + NR_ISOLATED_ANON + page_is_file_lru(page), + -compound_nr(page)); + unlock_page(page); + putback_lru_page(page); +} + +static void release_pte_pages(pte_t *pte, pte_t *_pte, + struct list_head *compound_pagelist) +{ + struct page *page, *tmp; + + while (--_pte >= pte) { + pte_t pteval = *_pte; + + page = pte_page(pteval); + if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) && + !PageCompound(page)) + release_pte_page(page); + } + + list_for_each_entry_safe(page, tmp, compound_pagelist, lru) { + list_del(&page->lru); + release_pte_page(page); + } +} + +static bool is_refcount_suitable(struct page *page) +{ + int expected_refcount; + + expected_refcount = total_mapcount(page); + if (PageSwapCache(page)) + expected_refcount += compound_nr(page); + + return page_count(page) == expected_refcount; +} + +static int __collapse_huge_page_isolate(struct vm_area_struct *vma, + unsigned long address, + pte_t *pte, + struct collapse_control *cc, + struct list_head *compound_pagelist) +{ + struct page *page = NULL; + pte_t *_pte; + int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0; + bool writable = false; + + for (_pte = pte; _pte < pte + HPAGE_PMD_NR; + _pte++, address += PAGE_SIZE) { + pte_t pteval = *_pte; + if (pte_none(pteval) || (pte_present(pteval) && + is_zero_pfn(pte_pfn(pteval)))) { + ++none_or_zero; + if (!userfaultfd_armed(vma) && + (!cc->is_khugepaged || + none_or_zero <= khugepaged_max_ptes_none)) { + continue; + } else { + result = SCAN_EXCEED_NONE_PTE; + count_vm_event(THP_SCAN_EXCEED_NONE_PTE); + goto out; + } + } + if (!pte_present(pteval)) { + result = SCAN_PTE_NON_PRESENT; + goto out; + } + if (pte_uffd_wp(pteval)) { + result = SCAN_PTE_UFFD_WP; + goto out; + } + page = vm_normal_page(vma, address, pteval); + if (unlikely(!page) || unlikely(is_zone_device_page(page))) { + result = SCAN_PAGE_NULL; + goto out; + } + + VM_BUG_ON_PAGE(!PageAnon(page), page); + + if (page_mapcount(page) > 1) { + ++shared; + if (cc->is_khugepaged && + shared > khugepaged_max_ptes_shared) { + result = SCAN_EXCEED_SHARED_PTE; + count_vm_event(THP_SCAN_EXCEED_SHARED_PTE); + goto out; + } + } + + if (PageCompound(page)) { + struct page *p; + page = compound_head(page); + + /* + * Check if we have dealt with the compound page + * already + */ + list_for_each_entry(p, compound_pagelist, lru) { + if (page == p) + goto next; + } + } + + /* + * We can do it before isolate_lru_page because the + * page can't be freed from under us. NOTE: PG_lock + * is needed to serialize against split_huge_page + * when invoked from the VM. + */ + if (!trylock_page(page)) { + result = SCAN_PAGE_LOCK; + goto out; + } + + /* + * Check if the page has any GUP (or other external) pins. + * + * The page table that maps the page has been already unlinked + * from the page table tree and this process cannot get + * an additional pin on the page. + * + * New pins can come later if the page is shared across fork, + * but not from this process. The other process cannot write to + * the page, only trigger CoW. + */ + if (!is_refcount_suitable(page)) { + unlock_page(page); + result = SCAN_PAGE_COUNT; + goto out; + } + + /* + * Isolate the page to avoid collapsing an hugepage + * currently in use by the VM. + */ + if (isolate_lru_page(page)) { + unlock_page(page); + result = SCAN_DEL_PAGE_LRU; + goto out; + } + mod_node_page_state(page_pgdat(page), + NR_ISOLATED_ANON + page_is_file_lru(page), + compound_nr(page)); + VM_BUG_ON_PAGE(!PageLocked(page), page); + VM_BUG_ON_PAGE(PageLRU(page), page); + + if (PageCompound(page)) + list_add_tail(&page->lru, compound_pagelist); +next: + /* + * If collapse was initiated by khugepaged, check that there is + * enough young pte to justify collapsing the page + */ + if (cc->is_khugepaged && + (pte_young(pteval) || page_is_young(page) || + PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm, + address))) + referenced++; + + if (pte_write(pteval)) + writable = true; + } + + if (unlikely(!writable)) { + result = SCAN_PAGE_RO; + } else if (unlikely(cc->is_khugepaged && !referenced)) { + result = SCAN_LACK_REFERENCED_PAGE; + } else { + result = SCAN_SUCCEED; + trace_mm_collapse_huge_page_isolate(page, none_or_zero, + referenced, writable, result); + return result; + } +out: + release_pte_pages(pte, _pte, compound_pagelist); + trace_mm_collapse_huge_page_isolate(page, none_or_zero, + referenced, writable, result); + return result; +} + +static void __collapse_huge_page_copy(pte_t *pte, struct page *page, + struct vm_area_struct *vma, + unsigned long address, + spinlock_t *ptl, + struct list_head *compound_pagelist) +{ + struct page *src_page, *tmp; + pte_t *_pte; + for (_pte = pte; _pte < pte + HPAGE_PMD_NR; + _pte++, page++, address += PAGE_SIZE) { + pte_t pteval = *_pte; + + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { + clear_user_highpage(page, address); + add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); + if (is_zero_pfn(pte_pfn(pteval))) { + /* + * ptl mostly unnecessary. + */ + spin_lock(ptl); + ptep_clear(vma->vm_mm, address, _pte); + spin_unlock(ptl); + } + } else { + src_page = pte_page(pteval); + copy_user_highpage(page, src_page, address, vma); + if (!PageCompound(src_page)) + release_pte_page(src_page); + /* + * ptl mostly unnecessary, but preempt has to + * be disabled to update the per-cpu stats + * inside page_remove_rmap(). + */ + spin_lock(ptl); + ptep_clear(vma->vm_mm, address, _pte); + page_remove_rmap(src_page, vma, false); + spin_unlock(ptl); + free_page_and_swap_cache(src_page); + } + } + + list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) { + list_del(&src_page->lru); + mod_node_page_state(page_pgdat(src_page), + NR_ISOLATED_ANON + page_is_file_lru(src_page), + -compound_nr(src_page)); + unlock_page(src_page); + free_swap_cache(src_page); + putback_lru_page(src_page); + } +} + +static void khugepaged_alloc_sleep(void) +{ + DEFINE_WAIT(wait); + + add_wait_queue(&khugepaged_wait, &wait); + __set_current_state(TASK_INTERRUPTIBLE|TASK_FREEZABLE); + schedule_timeout(msecs_to_jiffies(khugepaged_alloc_sleep_millisecs)); + remove_wait_queue(&khugepaged_wait, &wait); +} + +struct collapse_control khugepaged_collapse_control = { + .is_khugepaged = true, +}; + +static bool hpage_collapse_scan_abort(int nid, struct collapse_control *cc) +{ + int i; + + /* + * If node_reclaim_mode is disabled, then no extra effort is made to + * allocate memory locally. + */ + if (!node_reclaim_enabled()) + return false; + + /* If there is a count for this node already, it must be acceptable */ + if (cc->node_load[nid]) + return false; + + for (i = 0; i < MAX_NUMNODES; i++) { + if (!cc->node_load[i]) + continue; + if (node_distance(nid, i) > node_reclaim_distance) + return true; + } + return false; +} + +#define khugepaged_defrag() \ + (transparent_hugepage_flags & \ + (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)) + +/* Defrag for khugepaged will enter direct reclaim/compaction if necessary */ +static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void) +{ + return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT; +} + +#ifdef CONFIG_NUMA +static int hpage_collapse_find_target_node(struct collapse_control *cc) +{ + int nid, target_node = 0, max_value = 0; + + /* find first node with max normal pages hit */ + for (nid = 0; nid < MAX_NUMNODES; nid++) + if (cc->node_load[nid] > max_value) { + max_value = cc->node_load[nid]; + target_node = nid; + } + + for_each_online_node(nid) { + if (max_value == cc->node_load[nid]) + node_set(nid, cc->alloc_nmask); + } + + return target_node; +} +#else +static int hpage_collapse_find_target_node(struct collapse_control *cc) +{ + return 0; +} +#endif + +static bool hpage_collapse_alloc_page(struct page **hpage, gfp_t gfp, int node, + nodemask_t *nmask) +{ + *hpage = __alloc_pages(gfp, HPAGE_PMD_ORDER, node, nmask); + if (unlikely(!*hpage)) { + count_vm_event(THP_COLLAPSE_ALLOC_FAILED); + return false; + } + + prep_transhuge_page(*hpage); + count_vm_event(THP_COLLAPSE_ALLOC); + return true; +} + +/* + * If mmap_lock temporarily dropped, revalidate vma + * before taking mmap_lock. + * Returns enum scan_result value. + */ + +static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, + bool expect_anon, + struct vm_area_struct **vmap, + struct collapse_control *cc) +{ + struct vm_area_struct *vma; + + if (unlikely(hpage_collapse_test_exit(mm))) + return SCAN_ANY_PROCESS; + + *vmap = vma = find_vma(mm, address); + if (!vma) + return SCAN_VMA_NULL; + + if (!transhuge_vma_suitable(vma, address)) + return SCAN_ADDRESS_RANGE; + if (!hugepage_vma_check(vma, vma->vm_flags, false, false, + cc->is_khugepaged)) + return SCAN_VMA_CHECK; + /* + * Anon VMA expected, the address may be unmapped then + * remapped to file after khugepaged reaquired the mmap_lock. + * + * hugepage_vma_check may return true for qualified file + * vmas. + */ + if (expect_anon && (!(*vmap)->anon_vma || !vma_is_anonymous(*vmap))) + return SCAN_PAGE_ANON; + return SCAN_SUCCEED; +} + +/* + * See pmd_trans_unstable() for how the result may change out from + * underneath us, even if we hold mmap_lock in read. + */ +static int find_pmd_or_thp_or_none(struct mm_struct *mm, + unsigned long address, + pmd_t **pmd) +{ + pmd_t pmde; + + *pmd = mm_find_pmd(mm, address); + if (!*pmd) + return SCAN_PMD_NULL; + + pmde = pmd_read_atomic(*pmd); + +#ifdef CONFIG_TRANSPARENT_HUGEPAGE + /* See comments in pmd_none_or_trans_huge_or_clear_bad() */ + barrier(); +#endif + if (pmd_none(pmde)) + return SCAN_PMD_NONE; + if (!pmd_present(pmde)) + return SCAN_PMD_NULL; + if (pmd_trans_huge(pmde)) + return SCAN_PMD_MAPPED; + if (pmd_devmap(pmde)) + return SCAN_PMD_NULL; + if (pmd_bad(pmde)) + return SCAN_PMD_NULL; + return SCAN_SUCCEED; +} + +static int check_pmd_still_valid(struct mm_struct *mm, + unsigned long address, + pmd_t *pmd) +{ + pmd_t *new_pmd; + int result = find_pmd_or_thp_or_none(mm, address, &new_pmd); + + if (result != SCAN_SUCCEED) + return result; + if (new_pmd != pmd) + return SCAN_FAIL; + return SCAN_SUCCEED; +} + +/* + * Bring missing pages in from swap, to complete THP collapse. + * Only done if hpage_collapse_scan_pmd believes it is worthwhile. + * + * Called and returns without pte mapped or spinlocks held. + * Note that if false is returned, mmap_lock will be released. + */ + +static int __collapse_huge_page_swapin(struct mm_struct *mm, + struct vm_area_struct *vma, + unsigned long haddr, pmd_t *pmd, + int referenced) +{ + int swapped_in = 0; + vm_fault_t ret = 0; + unsigned long address, end = haddr + (HPAGE_PMD_NR * PAGE_SIZE); + + for (address = haddr; address < end; address += PAGE_SIZE) { + struct vm_fault vmf = { + .vma = vma, + .address = address, + .pgoff = linear_page_index(vma, haddr), + .flags = FAULT_FLAG_ALLOW_RETRY, + .pmd = pmd, + }; + + vmf.pte = pte_offset_map(pmd, address); + vmf.orig_pte = *vmf.pte; + if (!is_swap_pte(vmf.orig_pte)) { + pte_unmap(vmf.pte); + continue; + } + ret = do_swap_page(&vmf); + + /* + * do_swap_page returns VM_FAULT_RETRY with released mmap_lock. + * Note we treat VM_FAULT_RETRY as VM_FAULT_ERROR here because + * we do not retry here and swap entry will remain in pagetable + * resulting in later failure. + */ + if (ret & VM_FAULT_RETRY) { + trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); + /* Likely, but not guaranteed, that page lock failed */ + return SCAN_PAGE_LOCK; + } + if (ret & VM_FAULT_ERROR) { + mmap_read_unlock(mm); + trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); + return SCAN_FAIL; + } + swapped_in++; + } + + /* Drain LRU add pagevec to remove extra pin on the swapped in pages */ + if (swapped_in) + lru_add_drain(); + + trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1); + return SCAN_SUCCEED; +} + +static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm, + struct collapse_control *cc) +{ + gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() : + GFP_TRANSHUGE); + int node = hpage_collapse_find_target_node(cc); + + if (!hpage_collapse_alloc_page(hpage, gfp, node, &cc->alloc_nmask)) + return SCAN_ALLOC_HUGE_PAGE_FAIL; + if (unlikely(mem_cgroup_charge(page_folio(*hpage), mm, gfp))) + return SCAN_CGROUP_CHARGE_FAIL; + count_memcg_page_event(*hpage, THP_COLLAPSE_ALLOC); + return SCAN_SUCCEED; +} + +static int collapse_huge_page(struct mm_struct *mm, unsigned long address, + int referenced, int unmapped, + struct collapse_control *cc) +{ + LIST_HEAD(compound_pagelist); + pmd_t *pmd, _pmd; + pte_t *pte; + pgtable_t pgtable; + struct page *hpage; + spinlock_t *pmd_ptl, *pte_ptl; + int result = SCAN_FAIL; + struct vm_area_struct *vma; + struct mmu_notifier_range range; + + VM_BUG_ON(address & ~HPAGE_PMD_MASK); + + /* + * Before allocating the hugepage, release the mmap_lock read lock. + * The allocation can take potentially a long time if it involves + * sync compaction, and we do not need to hold the mmap_lock during + * that. We will recheck the vma after taking it again in write mode. + */ + mmap_read_unlock(mm); + + result = alloc_charge_hpage(&hpage, mm, cc); + if (result != SCAN_SUCCEED) + goto out_nolock; + + mmap_read_lock(mm); + result = hugepage_vma_revalidate(mm, address, true, &vma, cc); + if (result != SCAN_SUCCEED) { + mmap_read_unlock(mm); + goto out_nolock; + } + + result = find_pmd_or_thp_or_none(mm, address, &pmd); + if (result != SCAN_SUCCEED) { + mmap_read_unlock(mm); + goto out_nolock; + } + + if (unmapped) { + /* + * __collapse_huge_page_swapin will return with mmap_lock + * released when it fails. So we jump out_nolock directly in + * that case. Continuing to collapse causes inconsistency. + */ + result = __collapse_huge_page_swapin(mm, vma, address, pmd, + referenced); + if (result != SCAN_SUCCEED) + goto out_nolock; + } + + mmap_read_unlock(mm); + /* + * Prevent all access to pagetables with the exception of + * gup_fast later handled by the ptep_clear_flush and the VM + * handled by the anon_vma lock + PG_lock. + */ + mmap_write_lock(mm); + result = hugepage_vma_revalidate(mm, address, true, &vma, cc); + if (result != SCAN_SUCCEED) + goto out_up_write; + /* check if the pmd is still valid */ + result = check_pmd_still_valid(mm, address, pmd); + if (result != SCAN_SUCCEED) + goto out_up_write; + + anon_vma_lock_write(vma->anon_vma); + + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm, + address, address + HPAGE_PMD_SIZE); + mmu_notifier_invalidate_range_start(&range); + + pte = pte_offset_map(pmd, address); + pte_ptl = pte_lockptr(mm, pmd); + + pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */ + /* + * This removes any huge TLB entry from the CPU so we won't allow + * huge and small TLB entries for the same virtual address to + * avoid the risk of CPU bugs in that area. + * + * Parallel fast GUP is fine since fast GUP will back off when + * it detects PMD is changed. + */ + _pmd = pmdp_collapse_flush(vma, address, pmd); + spin_unlock(pmd_ptl); + mmu_notifier_invalidate_range_end(&range); + tlb_remove_table_sync_one(); + + spin_lock(pte_ptl); + result = __collapse_huge_page_isolate(vma, address, pte, cc, + &compound_pagelist); + spin_unlock(pte_ptl); + + if (unlikely(result != SCAN_SUCCEED)) { + pte_unmap(pte); + spin_lock(pmd_ptl); + BUG_ON(!pmd_none(*pmd)); + /* + * We can only use set_pmd_at when establishing + * hugepmds and never for establishing regular pmds that + * points to regular pagetables. Use pmd_populate for that + */ + pmd_populate(mm, pmd, pmd_pgtable(_pmd)); + spin_unlock(pmd_ptl); + anon_vma_unlock_write(vma->anon_vma); + goto out_up_write; + } + + /* + * All pages are isolated and locked so anon_vma rmap + * can't run anymore. + */ + anon_vma_unlock_write(vma->anon_vma); + + __collapse_huge_page_copy(pte, hpage, vma, address, pte_ptl, + &compound_pagelist); + pte_unmap(pte); + /* + * spin_lock() below is not the equivalent of smp_wmb(), but + * the smp_wmb() inside __SetPageUptodate() can be reused to + * avoid the copy_huge_page writes to become visible after + * the set_pmd_at() write. + */ + __SetPageUptodate(hpage); + pgtable = pmd_pgtable(_pmd); + + _pmd = mk_huge_pmd(hpage, vma->vm_page_prot); + _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma); + + spin_lock(pmd_ptl); + BUG_ON(!pmd_none(*pmd)); + page_add_new_anon_rmap(hpage, vma, address); + lru_cache_add_inactive_or_unevictable(hpage, vma); + pgtable_trans_huge_deposit(mm, pmd, pgtable); + set_pmd_at(mm, address, pmd, _pmd); + update_mmu_cache_pmd(vma, address, pmd); + spin_unlock(pmd_ptl); + + hpage = NULL; + + result = SCAN_SUCCEED; +out_up_write: + mmap_write_unlock(mm); +out_nolock: + if (hpage) { + mem_cgroup_uncharge(page_folio(hpage)); + put_page(hpage); + } + trace_mm_collapse_huge_page(mm, result == SCAN_SUCCEED, result); + return result; +} + +static int hpage_collapse_scan_pmd(struct mm_struct *mm, + struct vm_area_struct *vma, + unsigned long address, bool *mmap_locked, + struct collapse_control *cc) +{ + pmd_t *pmd; + pte_t *pte, *_pte; + int result = SCAN_FAIL, referenced = 0; + int none_or_zero = 0, shared = 0; + struct page *page = NULL; + unsigned long _address; + spinlock_t *ptl; + int node = NUMA_NO_NODE, unmapped = 0; + bool writable = false; + + VM_BUG_ON(address & ~HPAGE_PMD_MASK); + + result = find_pmd_or_thp_or_none(mm, address, &pmd); + if (result != SCAN_SUCCEED) + goto out; + + memset(cc->node_load, 0, sizeof(cc->node_load)); + nodes_clear(cc->alloc_nmask); + pte = pte_offset_map_lock(mm, pmd, address, &ptl); + for (_address = address, _pte = pte; _pte < pte + HPAGE_PMD_NR; + _pte++, _address += PAGE_SIZE) { + pte_t pteval = *_pte; + if (is_swap_pte(pteval)) { + ++unmapped; + if (!cc->is_khugepaged || + unmapped <= khugepaged_max_ptes_swap) { + /* + * Always be strict with uffd-wp + * enabled swap entries. Please see + * comment below for pte_uffd_wp(). + */ + if (pte_swp_uffd_wp(pteval)) { + result = SCAN_PTE_UFFD_WP; + goto out_unmap; + } + continue; + } else { + result = SCAN_EXCEED_SWAP_PTE; + count_vm_event(THP_SCAN_EXCEED_SWAP_PTE); + goto out_unmap; + } + } + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { + ++none_or_zero; + if (!userfaultfd_armed(vma) && + (!cc->is_khugepaged || + none_or_zero <= khugepaged_max_ptes_none)) { + continue; + } else { + result = SCAN_EXCEED_NONE_PTE; + count_vm_event(THP_SCAN_EXCEED_NONE_PTE); + goto out_unmap; + } + } + if (pte_uffd_wp(pteval)) { + /* + * Don't collapse the page if any of the small + * PTEs are armed with uffd write protection. + * Here we can also mark the new huge pmd as + * write protected if any of the small ones is + * marked but that could bring unknown + * userfault messages that falls outside of + * the registered range. So, just be simple. + */ + result = SCAN_PTE_UFFD_WP; + goto out_unmap; + } + if (pte_write(pteval)) + writable = true; + + page = vm_normal_page(vma, _address, pteval); + if (unlikely(!page) || unlikely(is_zone_device_page(page))) { + result = SCAN_PAGE_NULL; + goto out_unmap; + } + + if (page_mapcount(page) > 1) { + ++shared; + if (cc->is_khugepaged && + shared > khugepaged_max_ptes_shared) { + result = SCAN_EXCEED_SHARED_PTE; + count_vm_event(THP_SCAN_EXCEED_SHARED_PTE); + goto out_unmap; + } + } + + page = compound_head(page); + + /* + * Record which node the original page is from and save this + * information to cc->node_load[]. + * Khugepaged will allocate hugepage from the node has the max + * hit record. + */ + node = page_to_nid(page); + if (hpage_collapse_scan_abort(node, cc)) { + result = SCAN_SCAN_ABORT; + goto out_unmap; + } + cc->node_load[node]++; + if (!PageLRU(page)) { + result = SCAN_PAGE_LRU; + goto out_unmap; + } + if (PageLocked(page)) { + result = SCAN_PAGE_LOCK; + goto out_unmap; + } + if (!PageAnon(page)) { + result = SCAN_PAGE_ANON; + goto out_unmap; + } + + /* + * Check if the page has any GUP (or other external) pins. + * + * Here the check is racy it may see total_mapcount > refcount + * in some cases. + * For example, one process with one forked child process. + * The parent has the PMD split due to MADV_DONTNEED, then + * the child is trying unmap the whole PMD, but khugepaged + * may be scanning the parent between the child has + * PageDoubleMap flag cleared and dec the mapcount. So + * khugepaged may see total_mapcount > refcount. + * + * But such case is ephemeral we could always retry collapse + * later. However it may report false positive if the page + * has excessive GUP pins (i.e. 512). Anyway the same check + * will be done again later the risk seems low. + */ + if (!is_refcount_suitable(page)) { + result = SCAN_PAGE_COUNT; + goto out_unmap; + } + + /* + * If collapse was initiated by khugepaged, check that there is + * enough young pte to justify collapsing the page + */ + if (cc->is_khugepaged && + (pte_young(pteval) || page_is_young(page) || + PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm, + address))) + referenced++; + } + if (!writable) { + result = SCAN_PAGE_RO; + } else if (cc->is_khugepaged && + (!referenced || + (unmapped && referenced < HPAGE_PMD_NR / 2))) { + result = SCAN_LACK_REFERENCED_PAGE; + } else { + result = SCAN_SUCCEED; + } +out_unmap: + pte_unmap_unlock(pte, ptl); + if (result == SCAN_SUCCEED) { + result = collapse_huge_page(mm, address, referenced, + unmapped, cc); + /* collapse_huge_page will return with the mmap_lock released */ + *mmap_locked = false; + } +out: + trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, + none_or_zero, result, unmapped); + return result; +} + +static void collect_mm_slot(struct khugepaged_mm_slot *mm_slot) +{ + struct mm_slot *slot = &mm_slot->slot; + struct mm_struct *mm = slot->mm; + + lockdep_assert_held(&khugepaged_mm_lock); + + if (hpage_collapse_test_exit(mm)) { + /* free mm_slot */ + hash_del(&slot->hash); + list_del(&slot->mm_node); + + /* + * Not strictly needed because the mm exited already. + * + * clear_bit(MMF_VM_HUGEPAGE, &mm->flags); + */ + + /* khugepaged_mm_lock actually not necessary for the below */ + mm_slot_free(mm_slot_cache, mm_slot); + mmdrop(mm); + } +} + +#ifdef CONFIG_SHMEM +/* + * Notify khugepaged that given addr of the mm is pte-mapped THP. Then + * khugepaged should try to collapse the page table. + * + * Note that following race exists: + * (1) khugepaged calls khugepaged_collapse_pte_mapped_thps() for mm_struct A, + * emptying the A's ->pte_mapped_thp[] array. + * (2) MADV_COLLAPSE collapses some file extent with target mm_struct B, and + * retract_page_tables() finds a VMA in mm_struct A mapping the same extent + * (at virtual address X) and adds an entry (for X) into mm_struct A's + * ->pte-mapped_thp[] array. + * (3) khugepaged calls khugepaged_collapse_scan_file() for mm_struct A at X, + * sees a pte-mapped THP (SCAN_PTE_MAPPED_HUGEPAGE) and adds an entry + * (for X) into mm_struct A's ->pte-mapped_thp[] array. + * Thus, it's possible the same address is added multiple times for the same + * mm_struct. Should this happen, we'll simply attempt + * collapse_pte_mapped_thp() multiple times for the same address, under the same + * exclusive mmap_lock, and assuming the first call is successful, subsequent + * attempts will return quickly (without grabbing any additional locks) when + * a huge pmd is found in find_pmd_or_thp_or_none(). Since this is a cheap + * check, and since this is a rare occurrence, the cost of preventing this + * "multiple-add" is thought to be more expensive than just handling it, should + * it occur. + */ +static bool khugepaged_add_pte_mapped_thp(struct mm_struct *mm, + unsigned long addr) +{ + struct khugepaged_mm_slot *mm_slot; + struct mm_slot *slot; + bool ret = false; + + VM_BUG_ON(addr & ~HPAGE_PMD_MASK); + + spin_lock(&khugepaged_mm_lock); + slot = mm_slot_lookup(mm_slots_hash, mm); + mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot); + if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP)) { + mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr; + ret = true; + } + spin_unlock(&khugepaged_mm_lock); + return ret; +} + +/* hpage must be locked, and mmap_lock must be held in write */ +static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr, + pmd_t *pmdp, struct page *hpage) +{ + struct vm_fault vmf = { + .vma = vma, + .address = addr, + .flags = 0, + .pmd = pmdp, + }; + + VM_BUG_ON(!PageTransHuge(hpage)); + mmap_assert_write_locked(vma->vm_mm); + + if (do_set_pmd(&vmf, hpage)) + return SCAN_FAIL; + + get_page(hpage); + return SCAN_SUCCEED; +} + +/* + * A note about locking: + * Trying to take the page table spinlocks would be useless here because those + * are only used to synchronize: + * + * - modifying terminal entries (ones that point to a data page, not to another + * page table) + * - installing *new* non-terminal entries + * + * Instead, we need roughly the same kind of protection as free_pgtables() or + * mm_take_all_locks() (but only for a single VMA): + * The mmap lock together with this VMA's rmap locks covers all paths towards + * the page table entries we're messing with here, except for hardware page + * table walks and lockless_pages_from_mm(). + */ +static void collapse_and_free_pmd(struct mm_struct *mm, struct vm_area_struct *vma, + unsigned long addr, pmd_t *pmdp) +{ + pmd_t pmd; + struct mmu_notifier_range range; + + mmap_assert_write_locked(mm); + if (vma->vm_file) + lockdep_assert_held_write(&vma->vm_file->f_mapping->i_mmap_rwsem); + /* + * All anon_vmas attached to the VMA have the same root and are + * therefore locked by the same lock. + */ + if (vma->anon_vma) + lockdep_assert_held_write(&vma->anon_vma->root->rwsem); + + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm, addr, + addr + HPAGE_PMD_SIZE); + mmu_notifier_invalidate_range_start(&range); + pmd = pmdp_collapse_flush(vma, addr, pmdp); + tlb_remove_table_sync_one(); + mmu_notifier_invalidate_range_end(&range); + mm_dec_nr_ptes(mm); + page_table_check_pte_clear_range(mm, addr, pmd); + pte_free(mm, pmd_pgtable(pmd)); +} + +/** + * collapse_pte_mapped_thp - Try to collapse a pte-mapped THP for mm at + * address haddr. + * + * @mm: process address space where collapse happens + * @addr: THP collapse address + * @install_pmd: If a huge PMD should be installed + * + * This function checks whether all the PTEs in the PMD are pointing to the + * right THP. If so, retract the page table so the THP can refault in with + * as pmd-mapped. Possibly install a huge PMD mapping the THP. + */ +int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, + bool install_pmd) +{ + unsigned long haddr = addr & HPAGE_PMD_MASK; + struct vm_area_struct *vma = vma_lookup(mm, haddr); + struct page *hpage; + pte_t *start_pte, *pte; + pmd_t *pmd; + spinlock_t *ptl; + int count = 0, result = SCAN_FAIL; + int i; + + mmap_assert_write_locked(mm); + + /* Fast check before locking page if already PMD-mapped */ + result = find_pmd_or_thp_or_none(mm, haddr, &pmd); + if (result == SCAN_PMD_MAPPED) + return result; + + if (!vma || !vma->vm_file || + !range_in_vma(vma, haddr, haddr + HPAGE_PMD_SIZE)) + return SCAN_VMA_CHECK; + + /* + * If we are here, we've succeeded in replacing all the native pages + * in the page cache with a single hugepage. If a mm were to fault-in + * this memory (mapped by a suitably aligned VMA), we'd get the hugepage + * and map it by a PMD, regardless of sysfs THP settings. As such, let's + * analogously elide sysfs THP settings here. + */ + if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false)) + return SCAN_VMA_CHECK; + + /* Keep pmd pgtable for uffd-wp; see comment in retract_page_tables() */ + if (userfaultfd_wp(vma)) + return SCAN_PTE_UFFD_WP; + + hpage = find_lock_page(vma->vm_file->f_mapping, + linear_page_index(vma, haddr)); + if (!hpage) + return SCAN_PAGE_NULL; + + if (!PageHead(hpage)) { + result = SCAN_FAIL; + goto drop_hpage; + } + + if (compound_order(hpage) != HPAGE_PMD_ORDER) { + result = SCAN_PAGE_COMPOUND; + goto drop_hpage; + } + + switch (result) { + case SCAN_SUCCEED: + break; + case SCAN_PMD_NONE: + /* + * In MADV_COLLAPSE path, possible race with khugepaged where + * all pte entries have been removed and pmd cleared. If so, + * skip all the pte checks and just update the pmd mapping. + */ + goto maybe_install_pmd; + default: + goto drop_hpage; + } + + /* + * We need to lock the mapping so that from here on, only GUP-fast and + * hardware page walks can access the parts of the page tables that + * we're operating on. + * See collapse_and_free_pmd(). + */ + i_mmap_lock_write(vma->vm_file->f_mapping); + + /* + * This spinlock should be unnecessary: Nobody else should be accessing + * the page tables under spinlock protection here, only + * lockless_pages_from_mm() and the hardware page walker can access page + * tables while all the high-level locks are held in write mode. + */ + start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl); + result = SCAN_FAIL; + + /* step 1: check all mapped PTEs are to the right huge page */ + for (i = 0, addr = haddr, pte = start_pte; + i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) { + struct page *page; + + /* empty pte, skip */ + if (pte_none(*pte)) + continue; + + /* page swapped out, abort */ + if (!pte_present(*pte)) { + result = SCAN_PTE_NON_PRESENT; + goto abort; + } + + page = vm_normal_page(vma, addr, *pte); + if (WARN_ON_ONCE(page && is_zone_device_page(page))) + page = NULL; + /* + * Note that uprobe, debugger, or MAP_PRIVATE may change the + * page table, but the new page will not be a subpage of hpage. + */ + if (hpage + i != page) + goto abort; + count++; + } + + /* step 2: adjust rmap */ + for (i = 0, addr = haddr, pte = start_pte; + i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) { + struct page *page; + + if (pte_none(*pte)) + continue; + page = vm_normal_page(vma, addr, *pte); + if (WARN_ON_ONCE(page && is_zone_device_page(page))) + goto abort; + page_remove_rmap(page, vma, false); + } + + pte_unmap_unlock(start_pte, ptl); + + /* step 3: set proper refcount and mm_counters. */ + if (count) { + page_ref_sub(hpage, count); + add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count); + } + + /* step 4: remove pte entries */ + /* we make no change to anon, but protect concurrent anon page lookup */ + if (vma->anon_vma) + anon_vma_lock_write(vma->anon_vma); + + collapse_and_free_pmd(mm, vma, haddr, pmd); + + if (vma->anon_vma) + anon_vma_unlock_write(vma->anon_vma); + i_mmap_unlock_write(vma->vm_file->f_mapping); + +maybe_install_pmd: + /* step 5: install pmd entry */ + result = install_pmd + ? set_huge_pmd(vma, haddr, pmd, hpage) + : SCAN_SUCCEED; + +drop_hpage: + unlock_page(hpage); + put_page(hpage); + return result; + +abort: + pte_unmap_unlock(start_pte, ptl); + i_mmap_unlock_write(vma->vm_file->f_mapping); + goto drop_hpage; +} + +static void khugepaged_collapse_pte_mapped_thps(struct khugepaged_mm_slot *mm_slot) +{ + struct mm_slot *slot = &mm_slot->slot; + struct mm_struct *mm = slot->mm; + int i; + + if (likely(mm_slot->nr_pte_mapped_thp == 0)) + return; + + if (!mmap_write_trylock(mm)) + return; + + if (unlikely(hpage_collapse_test_exit(mm))) + goto out; + + for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++) + collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i], false); + +out: + mm_slot->nr_pte_mapped_thp = 0; + mmap_write_unlock(mm); +} + +static int retract_page_tables(struct address_space *mapping, pgoff_t pgoff, + struct mm_struct *target_mm, + unsigned long target_addr, struct page *hpage, + struct collapse_control *cc) +{ + struct vm_area_struct *vma; + int target_result = SCAN_FAIL; + + i_mmap_lock_write(mapping); + vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) { + int result = SCAN_FAIL; + struct mm_struct *mm = NULL; + unsigned long addr = 0; + pmd_t *pmd; + bool is_target = false; + + /* + * Check vma->anon_vma to exclude MAP_PRIVATE mappings that + * got written to. These VMAs are likely not worth investing + * mmap_write_lock(mm) as PMD-mapping is likely to be split + * later. + * + * Note that vma->anon_vma check is racy: it can be set up after + * the check but before we took mmap_lock by the fault path. + * But page lock would prevent establishing any new ptes of the + * page, so we are safe. + * + * An alternative would be drop the check, but check that page + * table is clear before calling pmdp_collapse_flush() under + * ptl. It has higher chance to recover THP for the VMA, but + * has higher cost too. It would also probably require locking + * the anon_vma. + */ + if (READ_ONCE(vma->anon_vma)) { + result = SCAN_PAGE_ANON; + goto next; + } + addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT); + if (addr & ~HPAGE_PMD_MASK || + vma->vm_end < addr + HPAGE_PMD_SIZE) { + result = SCAN_VMA_CHECK; + goto next; + } + mm = vma->vm_mm; + is_target = mm == target_mm && addr == target_addr; + result = find_pmd_or_thp_or_none(mm, addr, &pmd); + if (result != SCAN_SUCCEED) + goto next; + /* + * We need exclusive mmap_lock to retract page table. + * + * We use trylock due to lock inversion: we need to acquire + * mmap_lock while holding page lock. Fault path does it in + * reverse order. Trylock is a way to avoid deadlock. + * + * Also, it's not MADV_COLLAPSE's job to collapse other + * mappings - let khugepaged take care of them later. + */ + result = SCAN_PTE_MAPPED_HUGEPAGE; + if ((cc->is_khugepaged || is_target) && + mmap_write_trylock(mm)) { + /* + * Re-check whether we have an ->anon_vma, because + * collapse_and_free_pmd() requires that either no + * ->anon_vma exists or the anon_vma is locked. + * We already checked ->anon_vma above, but that check + * is racy because ->anon_vma can be populated under the + * mmap lock in read mode. + */ + if (vma->anon_vma) { + result = SCAN_PAGE_ANON; + goto unlock_next; + } + /* + * When a vma is registered with uffd-wp, we can't + * recycle the pmd pgtable because there can be pte + * markers installed. Skip it only, so the rest mm/vma + * can still have the same file mapped hugely, however + * it'll always mapped in small page size for uffd-wp + * registered ranges. + */ + if (hpage_collapse_test_exit(mm)) { + result = SCAN_ANY_PROCESS; + goto unlock_next; + } + if (userfaultfd_wp(vma)) { + result = SCAN_PTE_UFFD_WP; + goto unlock_next; + } + collapse_and_free_pmd(mm, vma, addr, pmd); + if (!cc->is_khugepaged && is_target) + result = set_huge_pmd(vma, addr, pmd, hpage); + else + result = SCAN_SUCCEED; + +unlock_next: + mmap_write_unlock(mm); + goto next; + } + /* + * Calling context will handle target mm/addr. Otherwise, let + * khugepaged try again later. + */ + if (!is_target) { + khugepaged_add_pte_mapped_thp(mm, addr); + continue; + } +next: + if (is_target) + target_result = result; + } + i_mmap_unlock_write(mapping); + return target_result; +} + +/** + * collapse_file - collapse filemap/tmpfs/shmem pages into huge one. + * + * @mm: process address space where collapse happens + * @addr: virtual collapse start address + * @file: file that collapse on + * @start: collapse start address + * @cc: collapse context and scratchpad + * + * Basic scheme is simple, details are more complex: + * - allocate and lock a new huge page; + * - scan page cache replacing old pages with the new one + * + swap/gup in pages if necessary; + * + fill in gaps; + * + keep old pages around in case rollback is required; + * - if replacing succeeds: + * + copy data over; + * + free old pages; + * + unlock huge page; + * - if replacing failed; + * + put all pages back and unfreeze them; + * + restore gaps in the page cache; + * + unlock and free huge page; + */ +static int collapse_file(struct mm_struct *mm, unsigned long addr, + struct file *file, pgoff_t start, + struct collapse_control *cc) +{ + struct address_space *mapping = file->f_mapping; + struct page *hpage; + pgoff_t index, end = start + HPAGE_PMD_NR; + LIST_HEAD(pagelist); + XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER); + int nr_none = 0, result = SCAN_SUCCEED; + bool is_shmem = shmem_file(file); + int nr; + + VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem); + VM_BUG_ON(start & (HPAGE_PMD_NR - 1)); + + result = alloc_charge_hpage(&hpage, mm, cc); + if (result != SCAN_SUCCEED) + goto out; + + /* + * Ensure we have slots for all the pages in the range. This is + * almost certainly a no-op because most of the pages must be present + */ + do { + xas_lock_irq(&xas); + xas_create_range(&xas); + if (!xas_error(&xas)) + break; + xas_unlock_irq(&xas); + if (!xas_nomem(&xas, GFP_KERNEL)) { + result = SCAN_FAIL; + goto out; + } + } while (1); + + __SetPageLocked(hpage); + if (is_shmem) + __SetPageSwapBacked(hpage); + hpage->index = start; + hpage->mapping = mapping; + + /* + * At this point the hpage is locked and not up-to-date. + * It's safe to insert it into the page cache, because nobody would + * be able to map it or use it in another way until we unlock it. + */ + + xas_set(&xas, start); + for (index = start; index < end; index++) { + struct page *page = xas_next(&xas); + struct folio *folio; + + VM_BUG_ON(index != xas.xa_index); + if (is_shmem) { + if (!page) { + /* + * Stop if extent has been truncated or + * hole-punched, and is now completely + * empty. + */ + if (index == start) { + if (!xas_next_entry(&xas, end - 1)) { + result = SCAN_TRUNCATED; + goto xa_locked; + } + xas_set(&xas, index); + } + if (!shmem_charge(mapping->host, 1)) { + result = SCAN_FAIL; + goto xa_locked; + } + xas_store(&xas, hpage); + nr_none++; + continue; + } + + if (xa_is_value(page) || !PageUptodate(page)) { + xas_unlock_irq(&xas); + /* swap in or instantiate fallocated page */ + if (shmem_get_folio(mapping->host, index, + &folio, SGP_NOALLOC)) { + result = SCAN_FAIL; + goto xa_unlocked; + } + page = folio_file_page(folio, index); + } else if (trylock_page(page)) { + get_page(page); + xas_unlock_irq(&xas); + } else { + result = SCAN_PAGE_LOCK; + goto xa_locked; + } + } else { /* !is_shmem */ + if (!page || xa_is_value(page)) { + xas_unlock_irq(&xas); + page_cache_sync_readahead(mapping, &file->f_ra, + file, index, + end - index); + /* drain pagevecs to help isolate_lru_page() */ + lru_add_drain(); + page = find_lock_page(mapping, index); + if (unlikely(page == NULL)) { + result = SCAN_FAIL; + goto xa_unlocked; + } + } else if (PageDirty(page)) { + /* + * khugepaged only works on read-only fd, + * so this page is dirty because it hasn't + * been flushed since first write. There + * won't be new dirty pages. + * + * Trigger async flush here and hope the + * writeback is done when khugepaged + * revisits this page. + * + * This is a one-off situation. We are not + * forcing writeback in loop. + */ + xas_unlock_irq(&xas); + filemap_flush(mapping); + result = SCAN_FAIL; + goto xa_unlocked; + } else if (PageWriteback(page)) { + xas_unlock_irq(&xas); + result = SCAN_FAIL; + goto xa_unlocked; + } else if (trylock_page(page)) { + get_page(page); + xas_unlock_irq(&xas); + } else { + result = SCAN_PAGE_LOCK; + goto xa_locked; + } + } + + /* + * The page must be locked, so we can drop the i_pages lock + * without racing with truncate. + */ + VM_BUG_ON_PAGE(!PageLocked(page), page); + + /* make sure the page is up to date */ + if (unlikely(!PageUptodate(page))) { + result = SCAN_FAIL; + goto out_unlock; + } + + /* + * If file was truncated then extended, or hole-punched, before + * we locked the first page, then a THP might be there already. + * This will be discovered on the first iteration. + */ + if (PageTransCompound(page)) { + struct page *head = compound_head(page); + + result = compound_order(head) == HPAGE_PMD_ORDER && + head->index == start + /* Maybe PMD-mapped */ + ? SCAN_PTE_MAPPED_HUGEPAGE + : SCAN_PAGE_COMPOUND; + goto out_unlock; + } + + folio = page_folio(page); + + if (folio_mapping(folio) != mapping) { + result = SCAN_TRUNCATED; + goto out_unlock; + } + + if (!is_shmem && (folio_test_dirty(folio) || + folio_test_writeback(folio))) { + /* + * khugepaged only works on read-only fd, so this + * page is dirty because it hasn't been flushed + * since first write. + */ + result = SCAN_FAIL; + goto out_unlock; + } + + if (folio_isolate_lru(folio)) { + result = SCAN_DEL_PAGE_LRU; + goto out_unlock; + } + + if (!filemap_release_folio(folio, GFP_KERNEL)) { + result = SCAN_PAGE_HAS_PRIVATE; + folio_putback_lru(folio); + goto out_unlock; + } + + if (folio_mapped(folio)) + try_to_unmap(folio, + TTU_IGNORE_MLOCK | TTU_BATCH_FLUSH); + + xas_lock_irq(&xas); + xas_set(&xas, index); + + VM_BUG_ON_PAGE(page != xas_load(&xas), page); + + /* + * The page is expected to have page_count() == 3: + * - we hold a pin on it; + * - one reference from page cache; + * - one from isolate_lru_page; + */ + if (!page_ref_freeze(page, 3)) { + result = SCAN_PAGE_COUNT; + xas_unlock_irq(&xas); + putback_lru_page(page); + goto out_unlock; + } + + /* + * Add the page to the list to be able to undo the collapse if + * something go wrong. + */ + list_add_tail(&page->lru, &pagelist); + + /* Finally, replace with the new page. */ + xas_store(&xas, hpage); + continue; +out_unlock: + unlock_page(page); + put_page(page); + goto xa_unlocked; + } + nr = thp_nr_pages(hpage); + + if (is_shmem) + __mod_lruvec_page_state(hpage, NR_SHMEM_THPS, nr); + else { + __mod_lruvec_page_state(hpage, NR_FILE_THPS, nr); + filemap_nr_thps_inc(mapping); + /* + * Paired with smp_mb() in do_dentry_open() to ensure + * i_writecount is up to date and the update to nr_thps is + * visible. Ensures the page cache will be truncated if the + * file is opened writable. + */ + smp_mb(); + if (inode_is_open_for_write(mapping->host)) { + result = SCAN_FAIL; + __mod_lruvec_page_state(hpage, NR_FILE_THPS, -nr); + filemap_nr_thps_dec(mapping); + goto xa_locked; + } + } + + if (nr_none) { + __mod_lruvec_page_state(hpage, NR_FILE_PAGES, nr_none); + /* nr_none is always 0 for non-shmem. */ + __mod_lruvec_page_state(hpage, NR_SHMEM, nr_none); + } + + /* Join all the small entries into a single multi-index entry */ + xas_set_order(&xas, start, HPAGE_PMD_ORDER); + xas_store(&xas, hpage); +xa_locked: + xas_unlock_irq(&xas); +xa_unlocked: + + /* + * If collapse is successful, flush must be done now before copying. + * If collapse is unsuccessful, does flush actually need to be done? + * Do it anyway, to clear the state. + */ + try_to_unmap_flush(); + + if (result == SCAN_SUCCEED) { + struct page *page, *tmp; + + /* + * Replacing old pages with new one has succeeded, now we + * need to copy the content and free the old pages. + */ + index = start; + list_for_each_entry_safe(page, tmp, &pagelist, lru) { + while (index < page->index) { + clear_highpage(hpage + (index % HPAGE_PMD_NR)); + index++; + } + copy_highpage(hpage + (page->index % HPAGE_PMD_NR), + page); + list_del(&page->lru); + page->mapping = NULL; + page_ref_unfreeze(page, 1); + ClearPageActive(page); + ClearPageUnevictable(page); + unlock_page(page); + put_page(page); + index++; + } + while (index < end) { + clear_highpage(hpage + (index % HPAGE_PMD_NR)); + index++; + } + + SetPageUptodate(hpage); + page_ref_add(hpage, HPAGE_PMD_NR - 1); + if (is_shmem) + set_page_dirty(hpage); + lru_cache_add(hpage); + + /* + * Remove pte page tables, so we can re-fault the page as huge. + */ + result = retract_page_tables(mapping, start, mm, addr, hpage, + cc); + unlock_page(hpage); + hpage = NULL; + } else { + struct page *page; + + /* Something went wrong: roll back page cache changes */ + xas_lock_irq(&xas); + if (nr_none) { + mapping->nrpages -= nr_none; + shmem_uncharge(mapping->host, nr_none); + } + + xas_set(&xas, start); + xas_for_each(&xas, page, end - 1) { + page = list_first_entry_or_null(&pagelist, + struct page, lru); + if (!page || xas.xa_index < page->index) { + if (!nr_none) + break; + nr_none--; + /* Put holes back where they were */ + xas_store(&xas, NULL); + continue; + } + + VM_BUG_ON_PAGE(page->index != xas.xa_index, page); + + /* Unfreeze the page. */ + list_del(&page->lru); + page_ref_unfreeze(page, 2); + xas_store(&xas, page); + xas_pause(&xas); + xas_unlock_irq(&xas); + unlock_page(page); + putback_lru_page(page); + xas_lock_irq(&xas); + } + VM_BUG_ON(nr_none); + xas_unlock_irq(&xas); + + hpage->mapping = NULL; + } + + if (hpage) + unlock_page(hpage); +out: + VM_BUG_ON(!list_empty(&pagelist)); + if (hpage) { + mem_cgroup_uncharge(page_folio(hpage)); + put_page(hpage); + } + /* TODO: tracepoints */ + return result; +} + +static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, + struct file *file, pgoff_t start, + struct collapse_control *cc) +{ + struct page *page = NULL; + struct address_space *mapping = file->f_mapping; + XA_STATE(xas, &mapping->i_pages, start); + int present, swap; + int node = NUMA_NO_NODE; + int result = SCAN_SUCCEED; + + present = 0; + swap = 0; + memset(cc->node_load, 0, sizeof(cc->node_load)); + nodes_clear(cc->alloc_nmask); + rcu_read_lock(); + xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) { + if (xas_retry(&xas, page)) + continue; + + if (xa_is_value(page)) { + ++swap; + if (cc->is_khugepaged && + swap > khugepaged_max_ptes_swap) { + result = SCAN_EXCEED_SWAP_PTE; + count_vm_event(THP_SCAN_EXCEED_SWAP_PTE); + break; + } + continue; + } + + /* + * TODO: khugepaged should compact smaller compound pages + * into a PMD sized page + */ + if (PageTransCompound(page)) { + struct page *head = compound_head(page); + + result = compound_order(head) == HPAGE_PMD_ORDER && + head->index == start + /* Maybe PMD-mapped */ + ? SCAN_PTE_MAPPED_HUGEPAGE + : SCAN_PAGE_COMPOUND; + /* + * For SCAN_PTE_MAPPED_HUGEPAGE, further processing + * by the caller won't touch the page cache, and so + * it's safe to skip LRU and refcount checks before + * returning. + */ + break; + } + + node = page_to_nid(page); + if (hpage_collapse_scan_abort(node, cc)) { + result = SCAN_SCAN_ABORT; + break; + } + cc->node_load[node]++; + + if (!PageLRU(page)) { + result = SCAN_PAGE_LRU; + break; + } + + if (page_count(page) != + 1 + page_mapcount(page) + page_has_private(page)) { + result = SCAN_PAGE_COUNT; + break; + } + + /* + * We probably should check if the page is referenced here, but + * nobody would transfer pte_young() to PageReferenced() for us. + * And rmap walk here is just too costly... + */ + + present++; + + if (need_resched()) { + xas_pause(&xas); + cond_resched_rcu(); + } + } + rcu_read_unlock(); + + if (result == SCAN_SUCCEED) { + if (cc->is_khugepaged && + present < HPAGE_PMD_NR - khugepaged_max_ptes_none) { + result = SCAN_EXCEED_NONE_PTE; + count_vm_event(THP_SCAN_EXCEED_NONE_PTE); + } else { + result = collapse_file(mm, addr, file, start, cc); + } + } + + trace_mm_khugepaged_scan_file(mm, page, file, present, swap, result); + return result; +} +#else +static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, + struct file *file, pgoff_t start, + struct collapse_control *cc) +{ + BUILD_BUG(); +} + +static void khugepaged_collapse_pte_mapped_thps(struct khugepaged_mm_slot *mm_slot) +{ +} + +static bool khugepaged_add_pte_mapped_thp(struct mm_struct *mm, + unsigned long addr) +{ + return false; +} +#endif + +static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result, + struct collapse_control *cc) + __releases(&khugepaged_mm_lock) + __acquires(&khugepaged_mm_lock) +{ + struct vma_iterator vmi; + struct khugepaged_mm_slot *mm_slot; + struct mm_slot *slot; + struct mm_struct *mm; + struct vm_area_struct *vma; + int progress = 0; + + VM_BUG_ON(!pages); + lockdep_assert_held(&khugepaged_mm_lock); + *result = SCAN_FAIL; + + if (khugepaged_scan.mm_slot) { + mm_slot = khugepaged_scan.mm_slot; + slot = &mm_slot->slot; + } else { + slot = list_entry(khugepaged_scan.mm_head.next, + struct mm_slot, mm_node); + mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot); + khugepaged_scan.address = 0; + khugepaged_scan.mm_slot = mm_slot; + } + spin_unlock(&khugepaged_mm_lock); + khugepaged_collapse_pte_mapped_thps(mm_slot); + + mm = slot->mm; + /* + * Don't wait for semaphore (to avoid long wait times). Just move to + * the next mm on the list. + */ + vma = NULL; + if (unlikely(!mmap_read_trylock(mm))) + goto breakouterloop_mmap_lock; + + progress++; + if (unlikely(hpage_collapse_test_exit(mm))) + goto breakouterloop; + + vma_iter_init(&vmi, mm, khugepaged_scan.address); + for_each_vma(vmi, vma) { + unsigned long hstart, hend; + + cond_resched(); + if (unlikely(hpage_collapse_test_exit(mm))) { + progress++; + break; + } + if (!hugepage_vma_check(vma, vma->vm_flags, false, false, true)) { +skip: + progress++; + continue; + } + hstart = round_up(vma->vm_start, HPAGE_PMD_SIZE); + hend = round_down(vma->vm_end, HPAGE_PMD_SIZE); + if (khugepaged_scan.address > hend) + goto skip; + if (khugepaged_scan.address < hstart) + khugepaged_scan.address = hstart; + VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK); + + while (khugepaged_scan.address < hend) { + bool mmap_locked = true; + + cond_resched(); + if (unlikely(hpage_collapse_test_exit(mm))) + goto breakouterloop; + + VM_BUG_ON(khugepaged_scan.address < hstart || + khugepaged_scan.address + HPAGE_PMD_SIZE > + hend); + if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) { + struct file *file = get_file(vma->vm_file); + pgoff_t pgoff = linear_page_index(vma, + khugepaged_scan.address); + + mmap_read_unlock(mm); + *result = hpage_collapse_scan_file(mm, + khugepaged_scan.address, + file, pgoff, cc); + mmap_locked = false; + fput(file); + } else { + *result = hpage_collapse_scan_pmd(mm, vma, + khugepaged_scan.address, + &mmap_locked, + cc); + } + switch (*result) { + case SCAN_PTE_MAPPED_HUGEPAGE: { + pmd_t *pmd; + + *result = find_pmd_or_thp_or_none(mm, + khugepaged_scan.address, + &pmd); + if (*result != SCAN_SUCCEED) + break; + if (!khugepaged_add_pte_mapped_thp(mm, + khugepaged_scan.address)) + break; + } fallthrough; + case SCAN_SUCCEED: + ++khugepaged_pages_collapsed; + break; + default: + break; + } + + /* move to next address */ + khugepaged_scan.address += HPAGE_PMD_SIZE; + progress += HPAGE_PMD_NR; + if (!mmap_locked) + /* + * We released mmap_lock so break loop. Note + * that we drop mmap_lock before all hugepage + * allocations, so if allocation fails, we are + * guaranteed to break here and report the + * correct result back to caller. + */ + goto breakouterloop_mmap_lock; + if (progress >= pages) + goto breakouterloop; + } + } +breakouterloop: + mmap_read_unlock(mm); /* exit_mmap will destroy ptes after this */ +breakouterloop_mmap_lock: + + spin_lock(&khugepaged_mm_lock); + VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot); + /* + * Release the current mm_slot if this mm is about to die, or + * if we scanned all vmas of this mm. + */ + if (hpage_collapse_test_exit(mm) || !vma) { + /* + * Make sure that if mm_users is reaching zero while + * khugepaged runs here, khugepaged_exit will find + * mm_slot not pointing to the exiting mm. + */ + if (slot->mm_node.next != &khugepaged_scan.mm_head) { + slot = list_entry(slot->mm_node.next, + struct mm_slot, mm_node); + khugepaged_scan.mm_slot = + mm_slot_entry(slot, struct khugepaged_mm_slot, slot); + khugepaged_scan.address = 0; + } else { + khugepaged_scan.mm_slot = NULL; + khugepaged_full_scans++; + } + + collect_mm_slot(mm_slot); + } + + return progress; +} + +static int khugepaged_has_work(void) +{ + return !list_empty(&khugepaged_scan.mm_head) && + hugepage_flags_enabled(); +} + +static int khugepaged_wait_event(void) +{ + return !list_empty(&khugepaged_scan.mm_head) || + kthread_should_stop(); +} + +static void khugepaged_do_scan(struct collapse_control *cc) +{ + unsigned int progress = 0, pass_through_head = 0; + unsigned int pages = READ_ONCE(khugepaged_pages_to_scan); + bool wait = true; + int result = SCAN_SUCCEED; + + lru_add_drain_all(); + + while (true) { + cond_resched(); + + if (unlikely(kthread_should_stop() || try_to_freeze())) + break; + + spin_lock(&khugepaged_mm_lock); + if (!khugepaged_scan.mm_slot) + pass_through_head++; + if (khugepaged_has_work() && + pass_through_head < 2) + progress += khugepaged_scan_mm_slot(pages - progress, + &result, cc); + else + progress = pages; + spin_unlock(&khugepaged_mm_lock); + + if (progress >= pages) + break; + + if (result == SCAN_ALLOC_HUGE_PAGE_FAIL) { + /* + * If fail to allocate the first time, try to sleep for + * a while. When hit again, cancel the scan. + */ + if (!wait) + break; + wait = false; + khugepaged_alloc_sleep(); + } + } +} + +static bool khugepaged_should_wakeup(void) +{ + return kthread_should_stop() || + time_after_eq(jiffies, khugepaged_sleep_expire); +} + +static void khugepaged_wait_work(void) +{ + if (khugepaged_has_work()) { + const unsigned long scan_sleep_jiffies = + msecs_to_jiffies(khugepaged_scan_sleep_millisecs); + + if (!scan_sleep_jiffies) + return; + + khugepaged_sleep_expire = jiffies + scan_sleep_jiffies; + wait_event_freezable_timeout(khugepaged_wait, + khugepaged_should_wakeup(), + scan_sleep_jiffies); + return; + } + + if (hugepage_flags_enabled()) + wait_event_freezable(khugepaged_wait, khugepaged_wait_event()); +} + +static int khugepaged(void *none) +{ + struct khugepaged_mm_slot *mm_slot; + + set_freezable(); + set_user_nice(current, MAX_NICE); + + while (!kthread_should_stop()) { + khugepaged_do_scan(&khugepaged_collapse_control); + khugepaged_wait_work(); + } + + spin_lock(&khugepaged_mm_lock); + mm_slot = khugepaged_scan.mm_slot; + khugepaged_scan.mm_slot = NULL; + if (mm_slot) + collect_mm_slot(mm_slot); + spin_unlock(&khugepaged_mm_lock); + return 0; +} + +static void set_recommended_min_free_kbytes(void) +{ + struct zone *zone; + int nr_zones = 0; + unsigned long recommended_min; + + if (!hugepage_flags_enabled()) { + calculate_min_free_kbytes(); + goto update_wmarks; + } + + for_each_populated_zone(zone) { + /* + * We don't need to worry about fragmentation of + * ZONE_MOVABLE since it only has movable pages. + */ + if (zone_idx(zone) > gfp_zone(GFP_USER)) + continue; + + nr_zones++; + } + + /* Ensure 2 pageblocks are free to assist fragmentation avoidance */ + recommended_min = pageblock_nr_pages * nr_zones * 2; + + /* + * Make sure that on average at least two pageblocks are almost free + * of another type, one for a migratetype to fall back to and a + * second to avoid subsequent fallbacks of other types There are 3 + * MIGRATE_TYPES we care about. + */ + recommended_min += pageblock_nr_pages * nr_zones * + MIGRATE_PCPTYPES * MIGRATE_PCPTYPES; + + /* don't ever allow to reserve more than 5% of the lowmem */ + recommended_min = min(recommended_min, + (unsigned long) nr_free_buffer_pages() / 20); + recommended_min <<= (PAGE_SHIFT-10); + + if (recommended_min > min_free_kbytes) { + if (user_min_free_kbytes >= 0) + pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n", + min_free_kbytes, recommended_min); + + min_free_kbytes = recommended_min; + } + +update_wmarks: + setup_per_zone_wmarks(); +} + +int start_stop_khugepaged(void) +{ + int err = 0; + + mutex_lock(&khugepaged_mutex); + if (hugepage_flags_enabled()) { + if (!khugepaged_thread) + khugepaged_thread = kthread_run(khugepaged, NULL, + "khugepaged"); + if (IS_ERR(khugepaged_thread)) { + pr_err("khugepaged: kthread_run(khugepaged) failed\n"); + err = PTR_ERR(khugepaged_thread); + khugepaged_thread = NULL; + goto fail; + } + + if (!list_empty(&khugepaged_scan.mm_head)) + wake_up_interruptible(&khugepaged_wait); + } else if (khugepaged_thread) { + kthread_stop(khugepaged_thread); + khugepaged_thread = NULL; + } + set_recommended_min_free_kbytes(); +fail: + mutex_unlock(&khugepaged_mutex); + return err; +} + +void khugepaged_min_free_kbytes_update(void) +{ + mutex_lock(&khugepaged_mutex); + if (hugepage_flags_enabled() && khugepaged_thread) + set_recommended_min_free_kbytes(); + mutex_unlock(&khugepaged_mutex); +} + +static int madvise_collapse_errno(enum scan_result r) +{ + /* + * MADV_COLLAPSE breaks from existing madvise(2) conventions to provide + * actionable feedback to caller, so they may take an appropriate + * fallback measure depending on the nature of the failure. + */ + switch (r) { + case SCAN_ALLOC_HUGE_PAGE_FAIL: + return -ENOMEM; + case SCAN_CGROUP_CHARGE_FAIL: + return -EBUSY; + /* Resource temporary unavailable - trying again might succeed */ + case SCAN_PAGE_COUNT: + case SCAN_PAGE_LOCK: + case SCAN_PAGE_LRU: + case SCAN_DEL_PAGE_LRU: + return -EAGAIN; + /* + * Other: Trying again likely not to succeed / error intrinsic to + * specified memory range. khugepaged likely won't be able to collapse + * either. + */ + default: + return -EINVAL; + } +} + +int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev, + unsigned long start, unsigned long end) +{ + struct collapse_control *cc; + struct mm_struct *mm = vma->vm_mm; + unsigned long hstart, hend, addr; + int thps = 0, last_fail = SCAN_FAIL; + bool mmap_locked = true; + + BUG_ON(vma->vm_start > start); + BUG_ON(vma->vm_end < end); + + *prev = vma; + + if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false)) + return -EINVAL; + + cc = kmalloc(sizeof(*cc), GFP_KERNEL); + if (!cc) + return -ENOMEM; + cc->is_khugepaged = false; + + mmgrab(mm); + lru_add_drain_all(); + + hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; + hend = end & HPAGE_PMD_MASK; + + for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { + int result = SCAN_FAIL; + + if (!mmap_locked) { + cond_resched(); + mmap_read_lock(mm); + mmap_locked = true; + result = hugepage_vma_revalidate(mm, addr, false, &vma, + cc); + if (result != SCAN_SUCCEED) { + last_fail = result; + goto out_nolock; + } + + hend = min(hend, vma->vm_end & HPAGE_PMD_MASK); + } + mmap_assert_locked(mm); + memset(cc->node_load, 0, sizeof(cc->node_load)); + nodes_clear(cc->alloc_nmask); + if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) { + struct file *file = get_file(vma->vm_file); + pgoff_t pgoff = linear_page_index(vma, addr); + + mmap_read_unlock(mm); + mmap_locked = false; + result = hpage_collapse_scan_file(mm, addr, file, pgoff, + cc); + fput(file); + } else { + result = hpage_collapse_scan_pmd(mm, vma, addr, + &mmap_locked, cc); + } + if (!mmap_locked) + *prev = NULL; /* Tell caller we dropped mmap_lock */ + +handle_result: + switch (result) { + case SCAN_SUCCEED: + case SCAN_PMD_MAPPED: + ++thps; + break; + case SCAN_PTE_MAPPED_HUGEPAGE: + BUG_ON(mmap_locked); + BUG_ON(*prev); + mmap_write_lock(mm); + result = collapse_pte_mapped_thp(mm, addr, true); + mmap_write_unlock(mm); + goto handle_result; + /* Whitelisted set of results where continuing OK */ + case SCAN_PMD_NULL: + case SCAN_PTE_NON_PRESENT: + case SCAN_PTE_UFFD_WP: + case SCAN_PAGE_RO: + case SCAN_LACK_REFERENCED_PAGE: + case SCAN_PAGE_NULL: + case SCAN_PAGE_COUNT: + case SCAN_PAGE_LOCK: + case SCAN_PAGE_COMPOUND: + case SCAN_PAGE_LRU: + case SCAN_DEL_PAGE_LRU: + last_fail = result; + break; + default: + last_fail = result; + /* Other error, exit */ + goto out_maybelock; + } + } + +out_maybelock: + /* Caller expects us to hold mmap_lock on return */ + if (!mmap_locked) + mmap_read_lock(mm); +out_nolock: + mmap_assert_locked(mm); + mmdrop(mm); + kfree(cc); + + return thps == ((hend - hstart) >> HPAGE_PMD_SHIFT) ? 0 + : madvise_collapse_errno(last_fail); +} |