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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
commit5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch)
treea94efe259b9009378be6d90eb30d2b019d95c194 /mm/khugepaged.c
parentInitial commit. (diff)
downloadlinux-5d1646d90e1f2cceb9f0828f4b28318cd0ec7744.tar.xz
linux-5d1646d90e1f2cceb9f0828f4b28318cd0ec7744.zip
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'mm/khugepaged.c')
-rw-r--r--mm/khugepaged.c2400
1 files changed, 2400 insertions, 0 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
new file mode 100644
index 000000000..28e18777e
--- /dev/null
+++ b/mm/khugepaged.c
@@ -0,0 +1,2400 @@
+// 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/swapops.h>
+#include <linux/shmem_fs.h>
+
+#include <asm/tlb.h>
+#include <asm/pgalloc.h>
+#include "internal.h"
+
+enum scan_result {
+ SCAN_FAIL,
+ SCAN_SUCCEED,
+ SCAN_PMD_NULL,
+ SCAN_EXCEED_NONE_PTE,
+ SCAN_EXCEED_SWAP_PTE,
+ SCAN_EXCEED_SHARED_PTE,
+ SCAN_PTE_NON_PRESENT,
+ SCAN_PTE_UFFD_WP,
+ 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_SWAP_CACHE_PAGE,
+ 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.
+ */
+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 mm_slot - hash lookup from mm to mm_slot
+ * @hash: hash collision list
+ * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
+ * @mm: the mm that this information is valid for
+ */
+struct mm_slot {
+ struct hlist_node hash;
+ struct list_head mm_node;
+ struct mm_struct *mm;
+
+ /* 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 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 sprintf(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 long msecs;
+ int err;
+
+ err = kstrtoul(buf, 10, &msecs);
+ if (err || msecs > UINT_MAX)
+ 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(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
+ scan_sleep_millisecs_store);
+
+static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sprintf(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 long msecs;
+ int err;
+
+ err = kstrtoul(buf, 10, &msecs);
+ if (err || msecs > UINT_MAX)
+ 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(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
+ alloc_sleep_millisecs_store);
+
+static ssize_t pages_to_scan_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sprintf(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)
+{
+ int err;
+ unsigned long pages;
+
+ err = kstrtoul(buf, 10, &pages);
+ if (err || !pages || pages > UINT_MAX)
+ return -EINVAL;
+
+ khugepaged_pages_to_scan = pages;
+
+ return count;
+}
+static struct kobj_attribute pages_to_scan_attr =
+ __ATTR(pages_to_scan, 0644, pages_to_scan_show,
+ pages_to_scan_store);
+
+static ssize_t pages_collapsed_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sprintf(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 sprintf(buf, "%u\n", khugepaged_full_scans);
+}
+static struct kobj_attribute full_scans_attr =
+ __ATTR_RO(full_scans);
+
+static ssize_t khugepaged_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 khugepaged_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(defrag, 0644, khugepaged_defrag_show,
+ khugepaged_defrag_store);
+
+/*
+ * 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 khugepaged_max_ptes_none_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
+}
+static ssize_t khugepaged_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(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
+ khugepaged_max_ptes_none_store);
+
+static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sprintf(buf, "%u\n", khugepaged_max_ptes_swap);
+}
+
+static ssize_t khugepaged_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(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
+ khugepaged_max_ptes_swap_store);
+
+static ssize_t khugepaged_max_ptes_shared_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sprintf(buf, "%u\n", khugepaged_max_ptes_shared);
+}
+
+static ssize_t khugepaged_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(max_ptes_shared, 0644, khugepaged_max_ptes_shared_show,
+ khugepaged_max_ptes_shared_store);
+
+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.
+ */
+ if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
+ khugepaged_enter_vma_merge(vma, *vm_flags))
+ return -ENOMEM;
+ 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 mm_slot),
+ __alignof__(struct 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 struct mm_slot *alloc_mm_slot(void)
+{
+ if (!mm_slot_cache) /* initialization failed */
+ return NULL;
+ return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
+}
+
+static inline void free_mm_slot(struct mm_slot *mm_slot)
+{
+ kmem_cache_free(mm_slot_cache, mm_slot);
+}
+
+static struct mm_slot *get_mm_slot(struct mm_struct *mm)
+{
+ struct mm_slot *mm_slot;
+
+ hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
+ if (mm == mm_slot->mm)
+ return mm_slot;
+
+ return NULL;
+}
+
+static void insert_to_mm_slots_hash(struct mm_struct *mm,
+ struct mm_slot *mm_slot)
+{
+ mm_slot->mm = mm;
+ hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
+}
+
+static inline int khugepaged_test_exit(struct mm_struct *mm)
+{
+ return atomic_read(&mm->mm_users) == 0;
+}
+
+static bool hugepage_vma_check(struct vm_area_struct *vma,
+ unsigned long vm_flags)
+{
+ if (!transhuge_vma_enabled(vma, vm_flags))
+ return false;
+
+ if (vma->vm_file && !IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
+ vma->vm_pgoff, HPAGE_PMD_NR))
+ return false;
+
+ /* Enabled via shmem mount options or sysfs settings. */
+ if (shmem_file(vma->vm_file))
+ return shmem_huge_enabled(vma);
+
+ /* THP settings require madvise. */
+ if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always())
+ return false;
+
+ /* Only regular file is valid */
+ if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file &&
+ (vm_flags & VM_DENYWRITE)) {
+ struct inode *inode = vma->vm_file->f_inode;
+
+ return S_ISREG(inode->i_mode);
+ }
+
+ if (!vma->anon_vma || vma->vm_ops)
+ return false;
+ if (vma_is_temporary_stack(vma))
+ return false;
+ return !(vm_flags & VM_NO_KHUGEPAGED);
+}
+
+int __khugepaged_enter(struct mm_struct *mm)
+{
+ struct mm_slot *mm_slot;
+ int wakeup;
+
+ mm_slot = alloc_mm_slot();
+ if (!mm_slot)
+ return -ENOMEM;
+
+ /* __khugepaged_exit() must not run from under us */
+ VM_BUG_ON_MM(atomic_read(&mm->mm_users) == 0, mm);
+ if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
+ free_mm_slot(mm_slot);
+ return 0;
+ }
+
+ spin_lock(&khugepaged_mm_lock);
+ insert_to_mm_slots_hash(mm, 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(&mm_slot->mm_node, &khugepaged_scan.mm_head);
+ spin_unlock(&khugepaged_mm_lock);
+
+ mmgrab(mm);
+ if (wakeup)
+ wake_up_interruptible(&khugepaged_wait);
+
+ return 0;
+}
+
+int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
+ unsigned long vm_flags)
+{
+ unsigned long hstart, hend;
+
+ /*
+ * khugepaged only supports read-only files for non-shmem files.
+ * khugepaged does not yet work on special mappings. And
+ * file-private shmem THP is not supported.
+ */
+ if (!hugepage_vma_check(vma, vm_flags))
+ return 0;
+
+ hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
+ hend = vma->vm_end & HPAGE_PMD_MASK;
+ if (hstart < hend)
+ return khugepaged_enter(vma, vm_flags);
+ return 0;
+}
+
+void __khugepaged_exit(struct mm_struct *mm)
+{
+ struct mm_slot *mm_slot;
+ int free = 0;
+
+ spin_lock(&khugepaged_mm_lock);
+ mm_slot = get_mm_slot(mm);
+ if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
+ hash_del(&mm_slot->hash);
+ list_del(&mm_slot->mm_node);
+ free = 1;
+ }
+ spin_unlock(&khugepaged_mm_lock);
+
+ if (free) {
+ clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
+ free_mm_slot(mm_slot);
+ mmdrop(mm);
+ } else if (mm_slot) {
+ /*
+ * This is required to serialize against
+ * khugepaged_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 list_head *compound_pagelist)
+{
+ struct page *page = NULL;
+ pte_t *_pte;
+ int none_or_zero = 0, shared = 0, result = 0, 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)))) {
+ if (!userfaultfd_armed(vma) &&
+ ++none_or_zero <= khugepaged_max_ptes_none) {
+ continue;
+ } else {
+ result = 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)) {
+ result = SCAN_PAGE_NULL;
+ goto out;
+ }
+
+ VM_BUG_ON_PAGE(!PageAnon(page), page);
+
+ if (page_mapcount(page) > 1 &&
+ ++shared > khugepaged_max_ptes_shared) {
+ result = 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 additinal 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;
+ }
+ if (!pte_write(pteval) && PageSwapCache(page) &&
+ !reuse_swap_page(page, NULL)) {
+ /*
+ * Page is in the swap cache and cannot be re-used.
+ * It cannot be collapsed into a THP.
+ */
+ unlock_page(page);
+ result = SCAN_SWAP_CACHE_PAGE;
+ 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:
+ /* There should be enough young pte to collapse the page */
+ if (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(!referenced)) {
+ result = SCAN_LACK_REFERENCED_PAGE;
+ } else {
+ result = SCAN_SUCCEED;
+ trace_mm_collapse_huge_page_isolate(page, none_or_zero,
+ referenced, writable, result);
+ return 1;
+ }
+out:
+ release_pte_pages(pte, _pte, compound_pagelist);
+ trace_mm_collapse_huge_page_isolate(page, none_or_zero,
+ referenced, writable, result);
+ return 0;
+}
+
+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);
+ /*
+ * paravirt calls inside pte_clear here are
+ * superfluous.
+ */
+ pte_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);
+ /*
+ * paravirt calls inside pte_clear here are
+ * superfluous.
+ */
+ pte_clear(vma->vm_mm, address, _pte);
+ page_remove_rmap(src_page, 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);
+ release_pte_page(src_page);
+ }
+}
+
+static void khugepaged_alloc_sleep(void)
+{
+ DEFINE_WAIT(wait);
+
+ add_wait_queue(&khugepaged_wait, &wait);
+ freezable_schedule_timeout_interruptible(
+ msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
+ remove_wait_queue(&khugepaged_wait, &wait);
+}
+
+static int khugepaged_node_load[MAX_NUMNODES];
+
+static bool khugepaged_scan_abort(int nid)
+{
+ int i;
+
+ /*
+ * If node_reclaim_mode is disabled, then no extra effort is made to
+ * allocate memory locally.
+ */
+ if (!node_reclaim_mode)
+ return false;
+
+ /* If there is a count for this node already, it must be acceptable */
+ if (khugepaged_node_load[nid])
+ return false;
+
+ for (i = 0; i < MAX_NUMNODES; i++) {
+ if (!khugepaged_node_load[i])
+ continue;
+ if (node_distance(nid, i) > node_reclaim_distance)
+ return true;
+ }
+ return false;
+}
+
+/* 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 khugepaged_find_target_node(void)
+{
+ static int last_khugepaged_target_node = NUMA_NO_NODE;
+ int nid, target_node = 0, max_value = 0;
+
+ /* find first node with max normal pages hit */
+ for (nid = 0; nid < MAX_NUMNODES; nid++)
+ if (khugepaged_node_load[nid] > max_value) {
+ max_value = khugepaged_node_load[nid];
+ target_node = nid;
+ }
+
+ /* do some balance if several nodes have the same hit record */
+ if (target_node <= last_khugepaged_target_node)
+ for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
+ nid++)
+ if (max_value == khugepaged_node_load[nid]) {
+ target_node = nid;
+ break;
+ }
+
+ last_khugepaged_target_node = target_node;
+ return target_node;
+}
+
+static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
+{
+ if (IS_ERR(*hpage)) {
+ if (!*wait)
+ return false;
+
+ *wait = false;
+ *hpage = NULL;
+ khugepaged_alloc_sleep();
+ } else if (*hpage) {
+ put_page(*hpage);
+ *hpage = NULL;
+ }
+
+ return true;
+}
+
+static struct page *
+khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
+{
+ VM_BUG_ON_PAGE(*hpage, *hpage);
+
+ *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
+ if (unlikely(!*hpage)) {
+ count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
+ *hpage = ERR_PTR(-ENOMEM);
+ return NULL;
+ }
+
+ prep_transhuge_page(*hpage);
+ count_vm_event(THP_COLLAPSE_ALLOC);
+ return *hpage;
+}
+#else
+static int khugepaged_find_target_node(void)
+{
+ return 0;
+}
+
+static inline struct page *alloc_khugepaged_hugepage(void)
+{
+ struct page *page;
+
+ page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
+ HPAGE_PMD_ORDER);
+ if (page)
+ prep_transhuge_page(page);
+ return page;
+}
+
+static struct page *khugepaged_alloc_hugepage(bool *wait)
+{
+ struct page *hpage;
+
+ do {
+ hpage = alloc_khugepaged_hugepage();
+ if (!hpage) {
+ count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
+ if (!*wait)
+ return NULL;
+
+ *wait = false;
+ khugepaged_alloc_sleep();
+ } else
+ count_vm_event(THP_COLLAPSE_ALLOC);
+ } while (unlikely(!hpage) && likely(khugepaged_enabled()));
+
+ return hpage;
+}
+
+static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
+{
+ /*
+ * If the hpage allocated earlier was briefly exposed in page cache
+ * before collapse_file() failed, it is possible that racing lookups
+ * have not yet completed, and would then be unpleasantly surprised by
+ * finding the hpage reused for the same mapping at a different offset.
+ * Just release the previous allocation if there is any danger of that.
+ */
+ if (*hpage && page_count(*hpage) > 1) {
+ put_page(*hpage);
+ *hpage = NULL;
+ }
+
+ if (!*hpage)
+ *hpage = khugepaged_alloc_hugepage(wait);
+
+ if (unlikely(!*hpage))
+ return false;
+
+ return true;
+}
+
+static struct page *
+khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
+{
+ VM_BUG_ON(!*hpage);
+
+ return *hpage;
+}
+#endif
+
+/*
+ * If mmap_lock temporarily dropped, revalidate vma
+ * before taking mmap_lock.
+ * Return 0 if succeeds, otherwise return none-zero
+ * value (scan code).
+ */
+
+static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
+ struct vm_area_struct **vmap)
+{
+ struct vm_area_struct *vma;
+ unsigned long hstart, hend;
+
+ if (unlikely(khugepaged_test_exit(mm)))
+ return SCAN_ANY_PROCESS;
+
+ *vmap = vma = find_vma(mm, address);
+ if (!vma)
+ return SCAN_VMA_NULL;
+
+ hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
+ hend = vma->vm_end & HPAGE_PMD_MASK;
+ if (address < hstart || address + HPAGE_PMD_SIZE > hend)
+ return SCAN_ADDRESS_RANGE;
+ if (!hugepage_vma_check(vma, vma->vm_flags))
+ return SCAN_VMA_CHECK;
+ /* Anon VMA expected */
+ if (!vma->anon_vma || vma->vm_ops)
+ return SCAN_VMA_CHECK;
+ return 0;
+}
+
+/*
+ * Bring missing pages in from swap, to complete THP collapse.
+ * Only done if khugepaged_scan_pmd believes it is worthwhile.
+ *
+ * Called and returns without pte mapped or spinlocks held,
+ * but with mmap_lock held to protect against vma changes.
+ */
+
+static bool __collapse_huge_page_swapin(struct mm_struct *mm,
+ struct vm_area_struct *vma,
+ unsigned long address, pmd_t *pmd,
+ int referenced)
+{
+ int swapped_in = 0;
+ vm_fault_t ret = 0;
+ struct vm_fault vmf = {
+ .vma = vma,
+ .address = address,
+ .flags = FAULT_FLAG_ALLOW_RETRY,
+ .pmd = pmd,
+ .pgoff = linear_page_index(vma, address),
+ };
+
+ vmf.pte = pte_offset_map(pmd, address);
+ for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
+ vmf.pte++, vmf.address += PAGE_SIZE) {
+ vmf.orig_pte = *vmf.pte;
+ if (!is_swap_pte(vmf.orig_pte))
+ continue;
+ swapped_in++;
+ ret = do_swap_page(&vmf);
+
+ /* do_swap_page returns VM_FAULT_RETRY with released mmap_lock */
+ if (ret & VM_FAULT_RETRY) {
+ mmap_read_lock(mm);
+ if (hugepage_vma_revalidate(mm, address, &vmf.vma)) {
+ /* vma is no longer available, don't continue to swapin */
+ trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
+ return false;
+ }
+ /* check if the pmd is still valid */
+ if (mm_find_pmd(mm, address) != pmd) {
+ trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
+ return false;
+ }
+ }
+ if (ret & VM_FAULT_ERROR) {
+ trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
+ return false;
+ }
+ /* pte is unmapped now, we need to map it */
+ vmf.pte = pte_offset_map(pmd, vmf.address);
+ }
+ vmf.pte--;
+ pte_unmap(vmf.pte);
+
+ /* 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 true;
+}
+
+static void collapse_huge_page(struct mm_struct *mm,
+ unsigned long address,
+ struct page **hpage,
+ int node, int referenced, int unmapped)
+{
+ LIST_HEAD(compound_pagelist);
+ pmd_t *pmd, _pmd;
+ pte_t *pte;
+ pgtable_t pgtable;
+ struct page *new_page;
+ spinlock_t *pmd_ptl, *pte_ptl;
+ int isolated = 0, result = 0;
+ struct vm_area_struct *vma;
+ struct mmu_notifier_range range;
+ gfp_t gfp;
+
+ VM_BUG_ON(address & ~HPAGE_PMD_MASK);
+
+ /* Only allocate from the target node */
+ gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
+
+ /*
+ * 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);
+ new_page = khugepaged_alloc_page(hpage, gfp, node);
+ if (!new_page) {
+ result = SCAN_ALLOC_HUGE_PAGE_FAIL;
+ goto out_nolock;
+ }
+
+ if (unlikely(mem_cgroup_charge(new_page, mm, gfp))) {
+ result = SCAN_CGROUP_CHARGE_FAIL;
+ goto out_nolock;
+ }
+ count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
+
+ mmap_read_lock(mm);
+ result = hugepage_vma_revalidate(mm, address, &vma);
+ if (result) {
+ mmap_read_unlock(mm);
+ goto out_nolock;
+ }
+
+ pmd = mm_find_pmd(mm, address);
+ if (!pmd) {
+ result = SCAN_PMD_NULL;
+ mmap_read_unlock(mm);
+ goto out_nolock;
+ }
+
+ /*
+ * __collapse_huge_page_swapin always returns with mmap_lock locked.
+ * If it fails, we release mmap_lock and jump out_nolock.
+ * Continuing to collapse causes inconsistency.
+ */
+ if (unmapped && !__collapse_huge_page_swapin(mm, vma, address,
+ pmd, referenced)) {
+ mmap_read_unlock(mm);
+ 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, &vma);
+ if (result)
+ goto out;
+ /* check if the pmd is still valid */
+ if (mm_find_pmd(mm, address) != pmd)
+ goto out;
+
+ 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);
+ isolated = __collapse_huge_page_isolate(vma, address, pte,
+ &compound_pagelist);
+ spin_unlock(pte_ptl);
+
+ if (unlikely(!isolated)) {
+ 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);
+ result = SCAN_FAIL;
+ goto out;
+ }
+
+ /*
+ * 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, new_page, vma, address, pte_ptl,
+ &compound_pagelist);
+ pte_unmap(pte);
+ __SetPageUptodate(new_page);
+ pgtable = pmd_pgtable(_pmd);
+
+ _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
+ _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
+
+ /*
+ * spin_lock() below is not the equivalent of smp_wmb(), so
+ * this is needed to avoid the copy_huge_page writes to become
+ * visible after the set_pmd_at() write.
+ */
+ smp_wmb();
+
+ spin_lock(pmd_ptl);
+ BUG_ON(!pmd_none(*pmd));
+ page_add_new_anon_rmap(new_page, vma, address, true);
+ lru_cache_add_inactive_or_unevictable(new_page, 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;
+
+ khugepaged_pages_collapsed++;
+ result = SCAN_SUCCEED;
+out_up_write:
+ mmap_write_unlock(mm);
+out_nolock:
+ if (!IS_ERR_OR_NULL(*hpage))
+ mem_cgroup_uncharge(*hpage);
+ trace_mm_collapse_huge_page(mm, isolated, result);
+ return;
+out:
+ goto out_up_write;
+}
+
+static int khugepaged_scan_pmd(struct mm_struct *mm,
+ struct vm_area_struct *vma,
+ unsigned long address,
+ struct page **hpage)
+{
+ pmd_t *pmd;
+ pte_t *pte, *_pte;
+ int ret = 0, result = 0, 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);
+
+ pmd = mm_find_pmd(mm, address);
+ if (!pmd) {
+ result = SCAN_PMD_NULL;
+ goto out;
+ }
+
+ memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
+ 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)) {
+ if (++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;
+ goto out_unmap;
+ }
+ }
+ if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
+ if (!userfaultfd_armed(vma) &&
+ ++none_or_zero <= khugepaged_max_ptes_none) {
+ continue;
+ } else {
+ result = SCAN_EXCEED_NONE_PTE;
+ goto out_unmap;
+ }
+ }
+ if (!pte_present(pteval)) {
+ result = SCAN_PTE_NON_PRESENT;
+ 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 uknown
+ * 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)) {
+ result = SCAN_PAGE_NULL;
+ goto out_unmap;
+ }
+
+ if (page_mapcount(page) > 1 &&
+ ++shared > khugepaged_max_ptes_shared) {
+ result = SCAN_EXCEED_SHARED_PTE;
+ goto out_unmap;
+ }
+
+ page = compound_head(page);
+
+ /*
+ * Record which node the original page is from and save this
+ * information to khugepaged_node_load[].
+ * Khupaged will allocate hugepage from the node has the max
+ * hit record.
+ */
+ node = page_to_nid(page);
+ if (khugepaged_scan_abort(node)) {
+ result = SCAN_SCAN_ABORT;
+ goto out_unmap;
+ }
+ khugepaged_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 totmal_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 (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 (!referenced || (unmapped && referenced < HPAGE_PMD_NR/2)) {
+ result = SCAN_LACK_REFERENCED_PAGE;
+ } else {
+ result = SCAN_SUCCEED;
+ ret = 1;
+ }
+out_unmap:
+ pte_unmap_unlock(pte, ptl);
+ if (ret) {
+ node = khugepaged_find_target_node();
+ /* collapse_huge_page will return with the mmap_lock released */
+ collapse_huge_page(mm, address, hpage, node,
+ referenced, unmapped);
+ }
+out:
+ trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
+ none_or_zero, result, unmapped);
+ return ret;
+}
+
+static void collect_mm_slot(struct mm_slot *mm_slot)
+{
+ struct mm_struct *mm = mm_slot->mm;
+
+ lockdep_assert_held(&khugepaged_mm_lock);
+
+ if (khugepaged_test_exit(mm)) {
+ /* free mm_slot */
+ hash_del(&mm_slot->hash);
+ list_del(&mm_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 */
+ free_mm_slot(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.
+ */
+static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
+ unsigned long addr)
+{
+ struct mm_slot *mm_slot;
+
+ VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
+
+ spin_lock(&khugepaged_mm_lock);
+ mm_slot = get_mm_slot(mm);
+ 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;
+ spin_unlock(&khugepaged_mm_lock);
+ return 0;
+}
+
+/**
+ * Try to collapse a pte-mapped THP for mm at address haddr.
+ *
+ * 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.
+ */
+void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
+{
+ unsigned long haddr = addr & HPAGE_PMD_MASK;
+ struct vm_area_struct *vma = find_vma(mm, haddr);
+ struct page *hpage;
+ pte_t *start_pte, *pte;
+ pmd_t *pmd, _pmd;
+ spinlock_t *ptl;
+ int count = 0;
+ int i;
+ struct mmu_notifier_range range;
+
+ if (!vma || !vma->vm_file ||
+ vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE)
+ return;
+
+ /*
+ * This vm_flags may not have VM_HUGEPAGE if the page was not
+ * collapsed by this mm. But we can still collapse if the page is
+ * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
+ * will not fail the vma for missing VM_HUGEPAGE
+ */
+ if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
+ return;
+
+ hpage = find_lock_page(vma->vm_file->f_mapping,
+ linear_page_index(vma, haddr));
+ if (!hpage)
+ return;
+
+ if (!PageHead(hpage))
+ goto drop_hpage;
+
+ pmd = mm_find_pmd(mm, haddr);
+ if (!pmd)
+ 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.
+ */
+ 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);
+
+ /* 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))
+ goto abort;
+
+ page = vm_normal_page(vma, addr, *pte);
+
+ /*
+ * 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);
+ page_remove_rmap(page, 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: collapse pmd */
+ /* we make no change to anon, but protect concurrent anon page lookup */
+ if (vma->anon_vma)
+ anon_vma_lock_write(vma->anon_vma);
+
+ mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm, haddr,
+ haddr + HPAGE_PMD_SIZE);
+ mmu_notifier_invalidate_range_start(&range);
+ _pmd = pmdp_collapse_flush(vma, haddr, pmd);
+ mm_dec_nr_ptes(mm);
+ tlb_remove_table_sync_one();
+ mmu_notifier_invalidate_range_end(&range);
+ pte_free(mm, pmd_pgtable(_pmd));
+
+ if (vma->anon_vma)
+ anon_vma_unlock_write(vma->anon_vma);
+ i_mmap_unlock_write(vma->vm_file->f_mapping);
+
+drop_hpage:
+ unlock_page(hpage);
+ put_page(hpage);
+ return;
+
+abort:
+ pte_unmap_unlock(start_pte, ptl);
+ i_mmap_unlock_write(vma->vm_file->f_mapping);
+ goto drop_hpage;
+}
+
+static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
+{
+ struct mm_struct *mm = mm_slot->mm;
+ int i;
+
+ if (likely(mm_slot->nr_pte_mapped_thp == 0))
+ return 0;
+
+ if (!mmap_write_trylock(mm))
+ return -EBUSY;
+
+ if (unlikely(khugepaged_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]);
+
+out:
+ mm_slot->nr_pte_mapped_thp = 0;
+ mmap_write_unlock(mm);
+ return 0;
+}
+
+static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
+{
+ struct vm_area_struct *vma;
+ struct mm_struct *mm;
+ unsigned long addr;
+ pmd_t *pmd, _pmd;
+
+ i_mmap_lock_write(mapping);
+ vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
+ /*
+ * 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.
+ *
+ * Not 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 (vma->anon_vma)
+ continue;
+ addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
+ if (addr & ~HPAGE_PMD_MASK)
+ continue;
+ if (vma->vm_end < addr + HPAGE_PMD_SIZE)
+ continue;
+ mm = vma->vm_mm;
+ pmd = mm_find_pmd(mm, addr);
+ if (!pmd)
+ continue;
+ /*
+ * 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.
+ */
+ if (mmap_write_trylock(mm)) {
+ if (!khugepaged_test_exit(mm)) {
+ struct mmu_notifier_range range;
+
+ mmu_notifier_range_init(&range,
+ MMU_NOTIFY_CLEAR, 0,
+ NULL, mm, addr,
+ addr + HPAGE_PMD_SIZE);
+ mmu_notifier_invalidate_range_start(&range);
+ /* assume page table is clear */
+ _pmd = pmdp_collapse_flush(vma, addr, pmd);
+ mm_dec_nr_ptes(mm);
+ tlb_remove_table_sync_one();
+ pte_free(mm, pmd_pgtable(_pmd));
+ mmu_notifier_invalidate_range_end(&range);
+ }
+ mmap_write_unlock(mm);
+ } else {
+ /* Try again later */
+ khugepaged_add_pte_mapped_thp(mm, addr);
+ }
+ }
+ i_mmap_unlock_write(mapping);
+}
+
+/**
+ * collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
+ *
+ * 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 void collapse_file(struct mm_struct *mm,
+ struct file *file, pgoff_t start,
+ struct page **hpage, int node)
+{
+ struct address_space *mapping = file->f_mapping;
+ gfp_t gfp;
+ struct page *new_page;
+ 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);
+
+ VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
+ VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
+
+ /* Only allocate from the target node */
+ gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
+
+ new_page = khugepaged_alloc_page(hpage, gfp, node);
+ if (!new_page) {
+ result = SCAN_ALLOC_HUGE_PAGE_FAIL;
+ goto out;
+ }
+
+ if (unlikely(mem_cgroup_charge(new_page, mm, gfp))) {
+ result = SCAN_CGROUP_CHARGE_FAIL;
+ goto out;
+ }
+ count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
+
+ /* This will be less messy when we use multi-index entries */
+ 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(new_page);
+ if (is_shmem)
+ __SetPageSwapBacked(new_page);
+ new_page->index = start;
+ new_page->mapping = mapping;
+
+ /*
+ * At this point the new_page 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);
+
+ 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, new_page);
+ nr_none++;
+ continue;
+ }
+
+ if (xa_is_value(page) || !PageUptodate(page)) {
+ xas_unlock_irq(&xas);
+ /* swap in or instantiate fallocated page */
+ if (shmem_getpage(mapping->host, index, &page,
+ SGP_NOHUGE)) {
+ 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;
+ }
+ } 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.
+ */
+ if (PageTransCompound(page)) {
+ result = SCAN_PAGE_COMPOUND;
+ goto out_unlock;
+ }
+
+ if (page_mapping(page) != mapping) {
+ result = SCAN_TRUNCATED;
+ goto out_unlock;
+ }
+
+ if (!is_shmem && (PageDirty(page) ||
+ PageWriteback(page))) {
+ /*
+ * 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 (isolate_lru_page(page)) {
+ result = SCAN_DEL_PAGE_LRU;
+ goto out_unlock;
+ }
+
+ if (page_has_private(page) &&
+ !try_to_release_page(page, GFP_KERNEL)) {
+ result = SCAN_PAGE_HAS_PRIVATE;
+ putback_lru_page(page);
+ goto out_unlock;
+ }
+
+ if (page_mapped(page))
+ unmap_mapping_pages(mapping, index, 1, false);
+
+ xas_lock_irq(&xas);
+ xas_set(&xas, index);
+
+ VM_BUG_ON_PAGE(page != xas_load(&xas), page);
+ VM_BUG_ON_PAGE(page_mapped(page), 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, new_page);
+ continue;
+out_unlock:
+ unlock_page(page);
+ put_page(page);
+ goto xa_unlocked;
+ }
+
+ if (is_shmem)
+ __inc_node_page_state(new_page, NR_SHMEM_THPS);
+ else {
+ __inc_node_page_state(new_page, NR_FILE_THPS);
+ filemap_nr_thps_inc(mapping);
+ }
+
+ if (nr_none) {
+ __mod_lruvec_page_state(new_page, NR_FILE_PAGES, nr_none);
+ if (is_shmem)
+ __mod_lruvec_page_state(new_page, NR_SHMEM, nr_none);
+ }
+
+xa_locked:
+ xas_unlock_irq(&xas);
+xa_unlocked:
+
+ 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(new_page + (index % HPAGE_PMD_NR));
+ index++;
+ }
+ copy_highpage(new_page + (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(new_page + (index % HPAGE_PMD_NR));
+ index++;
+ }
+
+ SetPageUptodate(new_page);
+ page_ref_add(new_page, HPAGE_PMD_NR - 1);
+ if (is_shmem)
+ set_page_dirty(new_page);
+ lru_cache_add(new_page);
+
+ /*
+ * Remove pte page tables, so we can re-fault the page as huge.
+ */
+ retract_page_tables(mapping, start);
+ *hpage = NULL;
+
+ khugepaged_pages_collapsed++;
+ } else {
+ struct page *page;
+
+ /* Something went wrong: roll back page cache changes */
+ xas_lock_irq(&xas);
+ mapping->nrpages -= nr_none;
+
+ if (is_shmem)
+ 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);
+
+ new_page->mapping = NULL;
+ }
+
+ unlock_page(new_page);
+out:
+ VM_BUG_ON(!list_empty(&pagelist));
+ if (!IS_ERR_OR_NULL(*hpage))
+ mem_cgroup_uncharge(*hpage);
+ /* TODO: tracepoints */
+}
+
+static void khugepaged_scan_file(struct mm_struct *mm,
+ struct file *file, pgoff_t start, struct page **hpage)
+{
+ 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(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
+ rcu_read_lock();
+ xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
+ if (xas_retry(&xas, page))
+ continue;
+
+ if (xa_is_value(page)) {
+ if (++swap > khugepaged_max_ptes_swap) {
+ result = SCAN_EXCEED_SWAP_PTE;
+ break;
+ }
+ continue;
+ }
+
+ if (PageTransCompound(page)) {
+ result = SCAN_PAGE_COMPOUND;
+ break;
+ }
+
+ node = page_to_nid(page);
+ if (khugepaged_scan_abort(node)) {
+ result = SCAN_SCAN_ABORT;
+ break;
+ }
+ khugepaged_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 (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
+ result = SCAN_EXCEED_NONE_PTE;
+ } else {
+ node = khugepaged_find_target_node();
+ collapse_file(mm, file, start, hpage, node);
+ }
+ }
+
+ /* TODO: tracepoints */
+}
+#else
+static void khugepaged_scan_file(struct mm_struct *mm,
+ struct file *file, pgoff_t start, struct page **hpage)
+{
+ BUILD_BUG();
+}
+
+static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
+{
+ return 0;
+}
+#endif
+
+static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
+ struct page **hpage)
+ __releases(&khugepaged_mm_lock)
+ __acquires(&khugepaged_mm_lock)
+{
+ struct mm_slot *mm_slot;
+ struct mm_struct *mm;
+ struct vm_area_struct *vma;
+ int progress = 0;
+
+ VM_BUG_ON(!pages);
+ lockdep_assert_held(&khugepaged_mm_lock);
+
+ if (khugepaged_scan.mm_slot)
+ mm_slot = khugepaged_scan.mm_slot;
+ else {
+ mm_slot = list_entry(khugepaged_scan.mm_head.next,
+ struct mm_slot, mm_node);
+ khugepaged_scan.address = 0;
+ khugepaged_scan.mm_slot = mm_slot;
+ }
+ spin_unlock(&khugepaged_mm_lock);
+ khugepaged_collapse_pte_mapped_thps(mm_slot);
+
+ mm = 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;
+ if (likely(!khugepaged_test_exit(mm)))
+ vma = find_vma(mm, khugepaged_scan.address);
+
+ progress++;
+ for (; vma; vma = vma->vm_next) {
+ unsigned long hstart, hend;
+
+ cond_resched();
+ if (unlikely(khugepaged_test_exit(mm))) {
+ progress++;
+ break;
+ }
+ if (!hugepage_vma_check(vma, vma->vm_flags)) {
+skip:
+ progress++;
+ continue;
+ }
+ hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
+ hend = vma->vm_end & HPAGE_PMD_MASK;
+ if (hstart >= hend)
+ goto skip;
+ 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);
+ if (shmem_file(vma->vm_file) && !shmem_huge_enabled(vma))
+ goto skip;
+
+ while (khugepaged_scan.address < hend) {
+ int ret;
+ cond_resched();
+ if (unlikely(khugepaged_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);
+ ret = 1;
+ khugepaged_scan_file(mm, file, pgoff, hpage);
+ fput(file);
+ } else {
+ ret = khugepaged_scan_pmd(mm, vma,
+ khugepaged_scan.address,
+ hpage);
+ }
+ /* move to next address */
+ khugepaged_scan.address += HPAGE_PMD_SIZE;
+ progress += HPAGE_PMD_NR;
+ if (ret)
+ /* we released mmap_lock so break loop */
+ 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 (khugepaged_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 (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
+ khugepaged_scan.mm_slot = list_entry(
+ mm_slot->mm_node.next,
+ struct mm_slot, mm_node);
+ 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) &&
+ khugepaged_enabled();
+}
+
+static int khugepaged_wait_event(void)
+{
+ return !list_empty(&khugepaged_scan.mm_head) ||
+ kthread_should_stop();
+}
+
+static void khugepaged_do_scan(void)
+{
+ struct page *hpage = NULL;
+ unsigned int progress = 0, pass_through_head = 0;
+ unsigned int pages = khugepaged_pages_to_scan;
+ bool wait = true;
+
+ barrier(); /* write khugepaged_pages_to_scan to local stack */
+
+ lru_add_drain_all();
+
+ while (progress < pages) {
+ if (!khugepaged_prealloc_page(&hpage, &wait))
+ break;
+
+ 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,
+ &hpage);
+ else
+ progress = pages;
+ spin_unlock(&khugepaged_mm_lock);
+ }
+
+ if (!IS_ERR_OR_NULL(hpage))
+ put_page(hpage);
+}
+
+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 (khugepaged_enabled())
+ wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
+}
+
+static int khugepaged(void *none)
+{
+ struct mm_slot *mm_slot;
+
+ set_freezable();
+ set_user_nice(current, MAX_NICE);
+
+ while (!kthread_should_stop()) {
+ khugepaged_do_scan();
+ 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;
+
+ 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;
+ }
+ setup_per_zone_wmarks();
+}
+
+int start_stop_khugepaged(void)
+{
+ int err = 0;
+
+ mutex_lock(&khugepaged_mutex);
+ if (khugepaged_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);
+
+ set_recommended_min_free_kbytes();
+ } else if (khugepaged_thread) {
+ kthread_stop(khugepaged_thread);
+ khugepaged_thread = NULL;
+ }
+fail:
+ mutex_unlock(&khugepaged_mutex);
+ return err;
+}
+
+void khugepaged_min_free_kbytes_update(void)
+{
+ mutex_lock(&khugepaged_mutex);
+ if (khugepaged_enabled() && khugepaged_thread)
+ set_recommended_min_free_kbytes();
+ mutex_unlock(&khugepaged_mutex);
+}