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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-11 08:27:49 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-11 08:27:49 +0000
commitace9429bb58fd418f0c81d4c2835699bddf6bde6 (patch)
treeb2d64bc10158fdd5497876388cd68142ca374ed3 /mm/khugepaged.c
parentInitial commit. (diff)
downloadlinux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.tar.xz
linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.zip
Adding upstream version 6.6.15.upstream/6.6.15
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r--mm/khugepaged.c2803
1 files changed, 2803 insertions, 0 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
new file mode 100644
index 0000000000..88433cc25d
--- /dev/null
+++ b/mm/khugepaged.c
@@ -0,0 +1,2803 @@
+// 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 <linux/ksm.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,
+ SCAN_STORE_FAILED,
+ SCAN_COPY_MC,
+ SCAN_PAGE_FILLED,
+};
+
+#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 DEFINE_READ_MOSTLY_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
+
+static struct kmem_cache *mm_slot_cache __read_mostly;
+
+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
+ */
+struct khugepaged_mm_slot {
+ struct mm_slot slot;
+};
+
+/**
+ * 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;
+
+ /* __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)))
+ return;
+
+ mm_slot = mm_slot_alloc(mm_slot_cache);
+ if (!mm_slot)
+ return;
+
+ slot = &mm_slot->slot;
+
+ 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_folio(struct folio *folio)
+{
+ node_stat_mod_folio(folio,
+ NR_ISOLATED_ANON + folio_is_file_lru(folio),
+ -folio_nr_pages(folio));
+ folio_unlock(folio);
+ folio_putback_lru(folio);
+}
+
+static void release_pte_page(struct page *page)
+{
+ release_pte_folio(page_folio(page));
+}
+
+static void release_pte_pages(pte_t *pte, pte_t *_pte,
+ struct list_head *compound_pagelist)
+{
+ struct folio *folio, *tmp;
+
+ while (--_pte >= pte) {
+ pte_t pteval = ptep_get(_pte);
+ unsigned long pfn;
+
+ if (pte_none(pteval))
+ continue;
+ pfn = pte_pfn(pteval);
+ if (is_zero_pfn(pfn))
+ continue;
+ folio = pfn_folio(pfn);
+ if (folio_test_large(folio))
+ continue;
+ release_pte_folio(folio);
+ }
+
+ list_for_each_entry_safe(folio, tmp, compound_pagelist, lru) {
+ list_del(&folio->lru);
+ release_pte_folio(folio);
+ }
+}
+
+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 = ptep_get(_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_succeeded(pte_t *pte,
+ struct vm_area_struct *vma,
+ unsigned long address,
+ spinlock_t *ptl,
+ struct list_head *compound_pagelist)
+{
+ struct page *src_page;
+ struct page *tmp;
+ pte_t *_pte;
+ pte_t pteval;
+
+ for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
+ _pte++, address += PAGE_SIZE) {
+ pteval = ptep_get(_pte);
+ if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
+ 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);
+ ksm_might_unmap_zero_page(vma->vm_mm, pteval);
+ }
+ } else {
+ src_page = pte_page(pteval);
+ 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 __collapse_huge_page_copy_failed(pte_t *pte,
+ pmd_t *pmd,
+ pmd_t orig_pmd,
+ struct vm_area_struct *vma,
+ struct list_head *compound_pagelist)
+{
+ spinlock_t *pmd_ptl;
+
+ /*
+ * Re-establish the PMD to point to the original page table
+ * entry. Restoring PMD needs to be done prior to releasing
+ * pages. Since pages are still isolated and locked here,
+ * acquiring anon_vma_lock_write is unnecessary.
+ */
+ pmd_ptl = pmd_lock(vma->vm_mm, pmd);
+ pmd_populate(vma->vm_mm, pmd, pmd_pgtable(orig_pmd));
+ spin_unlock(pmd_ptl);
+ /*
+ * Release both raw and compound pages isolated
+ * in __collapse_huge_page_isolate.
+ */
+ release_pte_pages(pte, pte + HPAGE_PMD_NR, compound_pagelist);
+}
+
+/*
+ * __collapse_huge_page_copy - attempts to copy memory contents from raw
+ * pages to a hugepage. Cleans up the raw pages if copying succeeds;
+ * otherwise restores the original page table and releases isolated raw pages.
+ * Returns SCAN_SUCCEED if copying succeeds, otherwise returns SCAN_COPY_MC.
+ *
+ * @pte: starting of the PTEs to copy from
+ * @page: the new hugepage to copy contents to
+ * @pmd: pointer to the new hugepage's PMD
+ * @orig_pmd: the original raw pages' PMD
+ * @vma: the original raw pages' virtual memory area
+ * @address: starting address to copy
+ * @ptl: lock on raw pages' PTEs
+ * @compound_pagelist: list that stores compound pages
+ */
+static int __collapse_huge_page_copy(pte_t *pte,
+ struct page *page,
+ pmd_t *pmd,
+ pmd_t orig_pmd,
+ struct vm_area_struct *vma,
+ unsigned long address,
+ spinlock_t *ptl,
+ struct list_head *compound_pagelist)
+{
+ struct page *src_page;
+ pte_t *_pte;
+ pte_t pteval;
+ unsigned long _address;
+ int result = SCAN_SUCCEED;
+
+ /*
+ * Copying pages' contents is subject to memory poison at any iteration.
+ */
+ for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR;
+ _pte++, page++, _address += PAGE_SIZE) {
+ pteval = ptep_get(_pte);
+ if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
+ clear_user_highpage(page, _address);
+ continue;
+ }
+ src_page = pte_page(pteval);
+ if (copy_mc_user_highpage(page, src_page, _address, vma) > 0) {
+ result = SCAN_COPY_MC;
+ break;
+ }
+ }
+
+ if (likely(result == SCAN_SUCCEED))
+ __collapse_huge_page_copy_succeeded(pte, vma, address, ptl,
+ compound_pagelist);
+ else
+ __collapse_huge_page_copy_failed(pte, pmd, orig_pmd, vma,
+ compound_pagelist);
+
+ return result;
+}
+
+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;
+ }
+
+ folio_prep_large_rmappable((struct folio *)*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;
+}
+
+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 = pmdp_get_lockless(*pmd);
+ 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.
+ * Returns result: if not SCAN_SUCCEED, mmap_lock has been 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);
+ int result;
+ pte_t *pte = NULL;
+ spinlock_t *ptl;
+
+ for (address = haddr; address < end; address += PAGE_SIZE) {
+ struct vm_fault vmf = {
+ .vma = vma,
+ .address = address,
+ .pgoff = linear_page_index(vma, address),
+ .flags = FAULT_FLAG_ALLOW_RETRY,
+ .pmd = pmd,
+ };
+
+ if (!pte++) {
+ pte = pte_offset_map_nolock(mm, pmd, address, &ptl);
+ if (!pte) {
+ mmap_read_unlock(mm);
+ result = SCAN_PMD_NULL;
+ goto out;
+ }
+ }
+
+ vmf.orig_pte = ptep_get_lockless(pte);
+ if (!is_swap_pte(vmf.orig_pte))
+ continue;
+
+ vmf.pte = pte;
+ vmf.ptl = ptl;
+ ret = do_swap_page(&vmf);
+ /* Which unmaps pte (after perhaps re-checking the entry) */
+ pte = NULL;
+
+ /*
+ * 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) {
+ /* Likely, but not guaranteed, that page lock failed */
+ result = SCAN_PAGE_LOCK;
+ goto out;
+ }
+ if (ret & VM_FAULT_ERROR) {
+ mmap_read_unlock(mm);
+ result = SCAN_FAIL;
+ goto out;
+ }
+ swapped_in++;
+ }
+
+ if (pte)
+ pte_unmap(pte);
+
+ /* Drain LRU cache to remove extra pin on the swapped in pages */
+ if (swapped_in)
+ lru_add_drain();
+
+ result = SCAN_SUCCEED;
+out:
+ trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, result);
+ return result;
+}
+
+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);
+ struct folio *folio;
+
+ if (!hpage_collapse_alloc_page(hpage, gfp, node, &cc->alloc_nmask))
+ return SCAN_ALLOC_HUGE_PAGE_FAIL;
+
+ folio = page_folio(*hpage);
+ if (unlikely(mem_cgroup_charge(folio, mm, gfp))) {
+ folio_put(folio);
+ *hpage = NULL;
+ 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;
+
+ vma_start_write(vma);
+ anon_vma_lock_write(vma->anon_vma);
+
+ mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, address,
+ address + HPAGE_PMD_SIZE);
+ mmu_notifier_invalidate_range_start(&range);
+
+ 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();
+
+ pte = pte_offset_map_lock(mm, &_pmd, address, &pte_ptl);
+ if (pte) {
+ result = __collapse_huge_page_isolate(vma, address, pte, cc,
+ &compound_pagelist);
+ spin_unlock(pte_ptl);
+ } else {
+ result = SCAN_PMD_NULL;
+ }
+
+ if (unlikely(result != SCAN_SUCCEED)) {
+ if (pte)
+ 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);
+
+ result = __collapse_huge_page_copy(pte, hpage, pmd, _pmd,
+ vma, address, pte_ptl,
+ &compound_pagelist);
+ pte_unmap(pte);
+ if (unlikely(result != SCAN_SUCCEED))
+ goto out_up_write;
+
+ /*
+ * 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)
+ 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);
+ if (!pte) {
+ result = SCAN_PMD_NULL;
+ goto out;
+ }
+
+ for (_address = address, _pte = pte; _pte < pte + HPAGE_PMD_NR;
+ _pte++, _address += PAGE_SIZE) {
+ pte_t pteval = ptep_get(_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_any(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 may be racy:
+ * it may see total_mapcount > refcount in some cases?
+ * 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
+/* hpage must be locked, and mmap_lock must be held */
+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_locked(vma->vm_mm);
+
+ if (do_set_pmd(&vmf, hpage))
+ return SCAN_FAIL;
+
+ get_page(hpage);
+ return SCAN_SUCCEED;
+}
+
+/**
+ * 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)
+{
+ struct mmu_notifier_range range;
+ bool notified = false;
+ 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, pgt_pmd;
+ spinlock_t *pml = NULL, *ptl;
+ int nr_ptes = 0, result = SCAN_FAIL;
+ int i;
+
+ mmap_assert_locked(mm);
+
+ /* First check VMA found, in case page tables are being torn down */
+ if (!vma || !vma->vm_file ||
+ !range_in_vma(vma, haddr, haddr + HPAGE_PMD_SIZE))
+ return SCAN_VMA_CHECK;
+
+ /* 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 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;
+ }
+
+ result = find_pmd_or_thp_or_none(mm, haddr, &pmd);
+ switch (result) {
+ case SCAN_SUCCEED:
+ break;
+ case SCAN_PMD_NONE:
+ /*
+ * All pte entries have been removed and pmd cleared.
+ * Skip all the pte checks and just update the pmd mapping.
+ */
+ goto maybe_install_pmd;
+ default:
+ goto drop_hpage;
+ }
+
+ result = SCAN_FAIL;
+ start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
+ if (!start_pte) /* mmap_lock + page lock should prevent this */
+ goto drop_hpage;
+
+ /* 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;
+ pte_t ptent = ptep_get(pte);
+
+ /* empty pte, skip */
+ if (pte_none(ptent))
+ continue;
+
+ /* page swapped out, abort */
+ if (!pte_present(ptent)) {
+ result = SCAN_PTE_NON_PRESENT;
+ goto abort;
+ }
+
+ page = vm_normal_page(vma, addr, ptent);
+ 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;
+ }
+
+ pte_unmap_unlock(start_pte, ptl);
+ mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
+ haddr, haddr + HPAGE_PMD_SIZE);
+ mmu_notifier_invalidate_range_start(&range);
+ notified = true;
+
+ /*
+ * pmd_lock covers a wider range than ptl, and (if split from mm's
+ * page_table_lock) ptl nests inside pml. The less time we hold pml,
+ * the better; but userfaultfd's mfill_atomic_pte() on a private VMA
+ * inserts a valid as-if-COWed PTE without even looking up page cache.
+ * So page lock of hpage does not protect from it, so we must not drop
+ * ptl before pgt_pmd is removed, so uffd private needs pml taken now.
+ */
+ if (userfaultfd_armed(vma) && !(vma->vm_flags & VM_SHARED))
+ pml = pmd_lock(mm, pmd);
+
+ start_pte = pte_offset_map_nolock(mm, pmd, haddr, &ptl);
+ if (!start_pte) /* mmap_lock + page lock should prevent this */
+ goto abort;
+ if (!pml)
+ spin_lock(ptl);
+ else if (ptl != pml)
+ spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
+
+ /* step 2: clear page table and adjust rmap */
+ for (i = 0, addr = haddr, pte = start_pte;
+ i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
+ struct page *page;
+ pte_t ptent = ptep_get(pte);
+
+ if (pte_none(ptent))
+ continue;
+ /*
+ * We dropped ptl after the first scan, to do the mmu_notifier:
+ * page lock stops more PTEs of the hpage being faulted in, but
+ * does not stop write faults COWing anon copies from existing
+ * PTEs; and does not stop those being swapped out or migrated.
+ */
+ if (!pte_present(ptent)) {
+ result = SCAN_PTE_NON_PRESENT;
+ goto abort;
+ }
+ page = vm_normal_page(vma, addr, ptent);
+ if (hpage + i != page)
+ goto abort;
+
+ /*
+ * Must clear entry, or a racing truncate may re-remove it.
+ * TLB flush can be left until pmdp_collapse_flush() does it.
+ * PTE dirty? Shmem page is already dirty; file is read-only.
+ */
+ ptep_clear(mm, addr, pte);
+ page_remove_rmap(page, vma, false);
+ nr_ptes++;
+ }
+
+ pte_unmap(start_pte);
+ if (!pml)
+ spin_unlock(ptl);
+
+ /* step 3: set proper refcount and mm_counters. */
+ if (nr_ptes) {
+ page_ref_sub(hpage, nr_ptes);
+ add_mm_counter(mm, mm_counter_file(hpage), -nr_ptes);
+ }
+
+ /* step 4: remove empty page table */
+ if (!pml) {
+ pml = pmd_lock(mm, pmd);
+ if (ptl != pml)
+ spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
+ }
+ pgt_pmd = pmdp_collapse_flush(vma, haddr, pmd);
+ pmdp_get_lockless_sync();
+ if (ptl != pml)
+ spin_unlock(ptl);
+ spin_unlock(pml);
+
+ mmu_notifier_invalidate_range_end(&range);
+
+ mm_dec_nr_ptes(mm);
+ page_table_check_pte_clear_range(mm, haddr, pgt_pmd);
+ pte_free_defer(mm, pmd_pgtable(pgt_pmd));
+
+maybe_install_pmd:
+ /* step 5: install pmd entry */
+ result = install_pmd
+ ? set_huge_pmd(vma, haddr, pmd, hpage)
+ : SCAN_SUCCEED;
+ goto drop_hpage;
+abort:
+ if (nr_ptes) {
+ flush_tlb_mm(mm);
+ page_ref_sub(hpage, nr_ptes);
+ add_mm_counter(mm, mm_counter_file(hpage), -nr_ptes);
+ }
+ if (start_pte)
+ pte_unmap_unlock(start_pte, ptl);
+ if (pml && pml != ptl)
+ spin_unlock(pml);
+ if (notified)
+ mmu_notifier_invalidate_range_end(&range);
+drop_hpage:
+ unlock_page(hpage);
+ put_page(hpage);
+ return result;
+}
+
+static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
+{
+ struct vm_area_struct *vma;
+
+ i_mmap_lock_read(mapping);
+ vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
+ struct mmu_notifier_range range;
+ struct mm_struct *mm;
+ unsigned long addr;
+ pmd_t *pmd, pgt_pmd;
+ spinlock_t *pml;
+ spinlock_t *ptl;
+ bool skipped_uffd = false;
+
+ /*
+ * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
+ * got written to. These VMAs are likely not worth removing
+ * page tables from, as PMD-mapping is likely to be split later.
+ */
+ if (READ_ONCE(vma->anon_vma))
+ continue;
+
+ addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
+ if (addr & ~HPAGE_PMD_MASK ||
+ vma->vm_end < addr + HPAGE_PMD_SIZE)
+ continue;
+
+ mm = vma->vm_mm;
+ if (find_pmd_or_thp_or_none(mm, addr, &pmd) != SCAN_SUCCEED)
+ continue;
+
+ if (hpage_collapse_test_exit(mm))
+ continue;
+ /*
+ * When a vma is registered with uffd-wp, we cannot recycle
+ * the page table because there may be pte markers installed.
+ * Other vmas can still have the same file mapped hugely, but
+ * skip this one: it will always be mapped in small page size
+ * for uffd-wp registered ranges.
+ */
+ if (userfaultfd_wp(vma))
+ continue;
+
+ /* PTEs were notified when unmapped; but now for the PMD? */
+ mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
+ addr, addr + HPAGE_PMD_SIZE);
+ mmu_notifier_invalidate_range_start(&range);
+
+ pml = pmd_lock(mm, pmd);
+ ptl = pte_lockptr(mm, pmd);
+ if (ptl != pml)
+ spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
+
+ /*
+ * Huge page lock is still held, so normally the page table
+ * must remain empty; and we have already skipped anon_vma
+ * and userfaultfd_wp() vmas. But since the mmap_lock is not
+ * held, it is still possible for a racing userfaultfd_ioctl()
+ * to have inserted ptes or markers. Now that we hold ptlock,
+ * repeating the anon_vma check protects from one category,
+ * and repeating the userfaultfd_wp() check from another.
+ */
+ if (unlikely(vma->anon_vma || userfaultfd_wp(vma))) {
+ skipped_uffd = true;
+ } else {
+ pgt_pmd = pmdp_collapse_flush(vma, addr, pmd);
+ pmdp_get_lockless_sync();
+ }
+
+ if (ptl != pml)
+ spin_unlock(ptl);
+ spin_unlock(pml);
+
+ mmu_notifier_invalidate_range_end(&range);
+
+ if (!skipped_uffd) {
+ mm_dec_nr_ptes(mm);
+ page_table_check_pte_clear_range(mm, addr, pgt_pmd);
+ pte_free_defer(mm, pmd_pgtable(pgt_pmd));
+ }
+ }
+ i_mmap_unlock_read(mapping);
+}
+
+/**
+ * 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, locking old pages
+ * + swap/gup in pages if necessary;
+ * - copy data to new page
+ * - handle shmem holes
+ * + re-validate that holes weren't filled by someone else
+ * + check for userfaultfd
+ * - finalize updates to the page cache;
+ * - if replacing succeeds:
+ * + unlock huge page;
+ * + free old pages;
+ * - if replacing failed;
+ * + unlock old pages
+ * + 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;
+ struct page *page;
+ struct page *tmp;
+ struct folio *folio;
+ pgoff_t index = 0, 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 = 0;
+
+ 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;
+
+ __SetPageLocked(hpage);
+ if (is_shmem)
+ __SetPageSwapBacked(hpage);
+ hpage->index = start;
+ hpage->mapping = mapping;
+
+ /*
+ * 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 rollback;
+ }
+ } while (1);
+
+ for (index = start; index < end; index++) {
+ xas_set(&xas, index);
+ page = xas_load(&xas);
+
+ 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;
+ }
+ }
+ 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;
+ }
+ /* drain lru cache to help isolate_lru_page() */
+ lru_add_drain();
+ 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 lru cache 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);
+
+ VM_BUG_ON_PAGE(page != xa_load(xas.xa, index), page);
+
+ /*
+ * We control three references to the page:
+ * - we hold a pin on it;
+ * - one reference from page cache;
+ * - one from isolate_lru_page;
+ * If those are the only references, then any new usage of the
+ * page will have to fetch it from the page cache. That requires
+ * locking the page to handle truncate, so any new usage will be
+ * blocked until we unlock page after collapse/during rollback.
+ */
+ if (page_count(page) != 3) {
+ result = SCAN_PAGE_COUNT;
+ xas_unlock_irq(&xas);
+ putback_lru_page(page);
+ goto out_unlock;
+ }
+
+ /*
+ * Accumulate the pages that are being collapsed.
+ */
+ list_add_tail(&page->lru, &pagelist);
+ continue;
+out_unlock:
+ unlock_page(page);
+ put_page(page);
+ goto xa_unlocked;
+ }
+
+ if (!is_shmem) {
+ 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;
+ filemap_nr_thps_dec(mapping);
+ }
+ }
+
+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 && nr_none &&
+ !shmem_charge(mapping->host, nr_none))
+ result = SCAN_FAIL;
+ if (result != SCAN_SUCCEED) {
+ nr_none = 0;
+ goto rollback;
+ }
+
+ /*
+ * The old pages are locked, so they won't change anymore.
+ */
+ index = start;
+ list_for_each_entry(page, &pagelist, lru) {
+ while (index < page->index) {
+ clear_highpage(hpage + (index % HPAGE_PMD_NR));
+ index++;
+ }
+ if (copy_mc_highpage(hpage + (page->index % HPAGE_PMD_NR), page) > 0) {
+ result = SCAN_COPY_MC;
+ goto rollback;
+ }
+ index++;
+ }
+ while (index < end) {
+ clear_highpage(hpage + (index % HPAGE_PMD_NR));
+ index++;
+ }
+
+ if (nr_none) {
+ struct vm_area_struct *vma;
+ int nr_none_check = 0;
+
+ i_mmap_lock_read(mapping);
+ xas_lock_irq(&xas);
+
+ xas_set(&xas, start);
+ for (index = start; index < end; index++) {
+ if (!xas_next(&xas)) {
+ xas_store(&xas, XA_RETRY_ENTRY);
+ if (xas_error(&xas)) {
+ result = SCAN_STORE_FAILED;
+ goto immap_locked;
+ }
+ nr_none_check++;
+ }
+ }
+
+ if (nr_none != nr_none_check) {
+ result = SCAN_PAGE_FILLED;
+ goto immap_locked;
+ }
+
+ /*
+ * If userspace observed a missing page in a VMA with a MODE_MISSING
+ * userfaultfd, then it might expect a UFFD_EVENT_PAGEFAULT for that
+ * page. If so, we need to roll back to avoid suppressing such an
+ * event. Since wp/minor userfaultfds don't give userspace any
+ * guarantees that the kernel doesn't fill a missing page with a zero
+ * page, so they don't matter here.
+ *
+ * Any userfaultfds registered after this point will not be able to
+ * observe any missing pages due to the previously inserted retry
+ * entries.
+ */
+ vma_interval_tree_foreach(vma, &mapping->i_mmap, start, end) {
+ if (userfaultfd_missing(vma)) {
+ result = SCAN_EXCEED_NONE_PTE;
+ goto immap_locked;
+ }
+ }
+
+immap_locked:
+ i_mmap_unlock_read(mapping);
+ if (result != SCAN_SUCCEED) {
+ xas_set(&xas, start);
+ for (index = start; index < end; index++) {
+ if (xas_next(&xas) == XA_RETRY_ENTRY)
+ xas_store(&xas, NULL);
+ }
+
+ xas_unlock_irq(&xas);
+ goto rollback;
+ }
+ } else {
+ xas_lock_irq(&xas);
+ }
+
+ 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);
+
+ 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);
+ }
+
+ /*
+ * Mark hpage as uptodate before inserting it into the page cache so
+ * that it isn't mistaken for an fallocated but unwritten page.
+ */
+ folio = page_folio(hpage);
+ folio_mark_uptodate(folio);
+ folio_ref_add(folio, HPAGE_PMD_NR - 1);
+
+ if (is_shmem)
+ folio_mark_dirty(folio);
+ folio_add_lru(folio);
+
+ /* Join all the small entries into a single multi-index entry. */
+ xas_set_order(&xas, start, HPAGE_PMD_ORDER);
+ xas_store(&xas, hpage);
+ WARN_ON_ONCE(xas_error(&xas));
+ xas_unlock_irq(&xas);
+
+ /*
+ * Remove pte page tables, so we can re-fault the page as huge.
+ * If MADV_COLLAPSE, adjust result to call collapse_pte_mapped_thp().
+ */
+ retract_page_tables(mapping, start);
+ if (cc && !cc->is_khugepaged)
+ result = SCAN_PTE_MAPPED_HUGEPAGE;
+ unlock_page(hpage);
+
+ /*
+ * The collapse has succeeded, so free the old pages.
+ */
+ list_for_each_entry_safe(page, tmp, &pagelist, lru) {
+ list_del(&page->lru);
+ page->mapping = NULL;
+ ClearPageActive(page);
+ ClearPageUnevictable(page);
+ unlock_page(page);
+ folio_put_refs(page_folio(page), 3);
+ }
+
+ goto out;
+
+rollback:
+ /* Something went wrong: roll back page cache changes */
+ if (nr_none) {
+ xas_lock_irq(&xas);
+ mapping->nrpages -= nr_none;
+ xas_unlock_irq(&xas);
+ shmem_uncharge(mapping->host, nr_none);
+ }
+
+ list_for_each_entry_safe(page, tmp, &pagelist, lru) {
+ list_del(&page->lru);
+ unlock_page(page);
+ putback_lru_page(page);
+ put_page(page);
+ }
+ /*
+ * Undo the updates of filemap_nr_thps_inc for non-SHMEM
+ * file only. This undo is not needed unless failure is
+ * due to SCAN_COPY_MC.
+ */
+ if (!is_shmem && result == SCAN_COPY_MC) {
+ filemap_nr_thps_dec(mapping);
+ /*
+ * Paired with smp_mb() in do_dentry_open() to
+ * ensure the update to nr_thps is visible.
+ */
+ smp_mb();
+ }
+
+ hpage->mapping = NULL;
+
+ unlock_page(hpage);
+ put_page(hpage);
+out:
+ VM_BUG_ON(!list_empty(&pagelist));
+ trace_mm_khugepaged_collapse_file(mm, hpage, index, is_shmem, addr, file, nr, result);
+ 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();
+}
+#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);
+
+ 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);
+ mmap_locked = false;
+ *result = hpage_collapse_scan_file(mm,
+ khugepaged_scan.address, file, pgoff, cc);
+ fput(file);
+ if (*result == SCAN_PTE_MAPPED_HUGEPAGE) {
+ mmap_read_lock(mm);
+ if (hpage_collapse_test_exit(mm))
+ goto breakouterloop;
+ *result = collapse_pte_mapped_thp(mm,
+ khugepaged_scan.address, false);
+ if (*result == SCAN_PMD_MAPPED)
+ *result = SCAN_SUCCEED;
+ mmap_read_unlock(mm);
+ }
+ } else {
+ *result = hpage_collapse_scan_pmd(mm, vma,
+ khugepaged_scan.address, &mmap_locked, cc);
+ }
+
+ if (*result == SCAN_SUCCEED)
+ ++khugepaged_pages_collapsed;
+
+ /* 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);
+}
+
+bool current_is_khugepaged(void)
+{
+ return kthread_func(current) == khugepaged;
+}
+
+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:
+ case SCAN_EXCEED_NONE_PTE:
+ 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:
+ case SCAN_PAGE_FILLED:
+ 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_read_lock(mm);
+ result = collapse_pte_mapped_thp(mm, addr, true);
+ mmap_read_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);
+}