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-rw-r--r--mm/khugepaged.c1490
1 files changed, 1490 insertions, 0 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
new file mode 100644
index 000000000000..3e6d1a1b7e2c
--- /dev/null
+++ b/mm/khugepaged.c
@@ -0,0 +1,1490 @@
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/mm.h>
+#include <linux/sched.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 <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_PTE_NON_PRESENT,
+ SCAN_PAGE_RO,
+ SCAN_NO_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_EXCEED_SWAP_PTE
+};
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/huge_memory.h>
+
+/* 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;
+
+#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;
+
+/**
+ * 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;
+};
+
+/**
+ * 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),
+};
+
+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 struct attribute *khugepaged_attr[] = {
+ &khugepaged_defrag_attr.attr,
+ &khugepaged_max_ptes_none_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,
+ &khugepaged_max_ptes_swap_attr.attr,
+ NULL,
+};
+
+struct attribute_group khugepaged_attr_group = {
+ .attrs = khugepaged_attr,
+ .name = "khugepaged",
+};
+
+#define VM_NO_KHUGEPAGED (VM_SPECIAL | VM_HUGETLB | VM_SHARED | VM_MAYSHARE)
+
+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;
+
+ 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;
+}
+
+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(khugepaged_test_exit(mm), 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);
+
+ atomic_inc(&mm->mm_count);
+ 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;
+ if (!vma->anon_vma)
+ /*
+ * Not yet faulted in so we will register later in the
+ * page fault if needed.
+ */
+ return 0;
+ if (vma->vm_ops || (vm_flags & VM_NO_KHUGEPAGED))
+ /* khugepaged not yet working on file or special mappings */
+ 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_sem.
+ */
+ down_write(&mm->mmap_sem);
+ up_write(&mm->mmap_sem);
+ }
+}
+
+static void release_pte_page(struct page *page)
+{
+ /* 0 stands for page_is_file_cache(page) == false */
+ dec_zone_page_state(page, NR_ISOLATED_ANON + 0);
+ unlock_page(page);
+ putback_lru_page(page);
+}
+
+static void release_pte_pages(pte_t *pte, pte_t *_pte)
+{
+ while (--_pte >= pte) {
+ pte_t pteval = *_pte;
+ if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
+ release_pte_page(pte_page(pteval));
+ }
+}
+
+static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
+ unsigned long address,
+ pte_t *pte)
+{
+ struct page *page = NULL;
+ pte_t *_pte;
+ int none_or_zero = 0, result = 0;
+ bool referenced = false, 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;
+ }
+ page = vm_normal_page(vma, address, pteval);
+ if (unlikely(!page)) {
+ result = SCAN_PAGE_NULL;
+ goto out;
+ }
+
+ VM_BUG_ON_PAGE(PageCompound(page), page);
+ VM_BUG_ON_PAGE(!PageAnon(page), page);
+ VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
+
+ /*
+ * 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;
+ }
+
+ /*
+ * cannot use mapcount: can't collapse if there's a gup pin.
+ * The page must only be referenced by the scanned process
+ * and page swap cache.
+ */
+ if (page_count(page) != 1 + !!PageSwapCache(page)) {
+ unlock_page(page);
+ result = SCAN_PAGE_COUNT;
+ goto out;
+ }
+ if (pte_write(pteval)) {
+ writable = true;
+ } else {
+ if (PageSwapCache(page) &&
+ !reuse_swap_page(page, NULL)) {
+ unlock_page(page);
+ result = SCAN_SWAP_CACHE_PAGE;
+ goto out;
+ }
+ /*
+ * Page is not in the swap cache. It can be collapsed
+ * into a THP.
+ */
+ }
+
+ /*
+ * 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;
+ }
+ /* 0 stands for page_is_file_cache(page) == false */
+ inc_zone_page_state(page, NR_ISOLATED_ANON + 0);
+ VM_BUG_ON_PAGE(!PageLocked(page), page);
+ VM_BUG_ON_PAGE(PageLRU(page), page);
+
+ /* If there is no mapped pte young don't collapse the page */
+ if (pte_young(pteval) ||
+ page_is_young(page) || PageReferenced(page) ||
+ mmu_notifier_test_young(vma->vm_mm, address))
+ referenced = true;
+ }
+ if (likely(writable)) {
+ if (likely(referenced)) {
+ result = SCAN_SUCCEED;
+ trace_mm_collapse_huge_page_isolate(page, none_or_zero,
+ referenced, writable, result);
+ return 1;
+ }
+ } else {
+ result = SCAN_PAGE_RO;
+ }
+
+out:
+ release_pte_pages(pte, _pte);
+ 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)
+{
+ pte_t *_pte;
+ for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
+ pte_t pteval = *_pte;
+ struct page *src_page;
+
+ 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);
+ VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, 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);
+ }
+
+ address += PAGE_SIZE;
+ 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 zone_reclaim_mode is disabled, then no extra effort is made to
+ * allocate memory locally.
+ */
+ if (!zone_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) > 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 GFP_TRANSHUGE | (khugepaged_defrag() ? __GFP_DIRECT_RECLAIM : 0);
+}
+
+#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, struct mm_struct *mm,
+ unsigned long address, int node)
+{
+ VM_BUG_ON_PAGE(*hpage, *hpage);
+
+ /*
+ * Before allocating the hugepage, release the mmap_sem read lock.
+ * The allocation can take potentially a long time if it involves
+ * sync compaction, and we do not need to hold the mmap_sem during
+ * that. We will recheck the vma after taking it again in write mode.
+ */
+ up_read(&mm->mmap_sem);
+
+ *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 (!*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, struct mm_struct *mm,
+ unsigned long address, int node)
+{
+ up_read(&mm->mmap_sem);
+ VM_BUG_ON(!*hpage);
+
+ return *hpage;
+}
+#endif
+
+static bool hugepage_vma_check(struct vm_area_struct *vma)
+{
+ if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
+ (vma->vm_flags & VM_NOHUGEPAGE))
+ return false;
+ if (!vma->anon_vma || vma->vm_ops)
+ return false;
+ if (is_vma_temporary_stack(vma))
+ return false;
+ return !(vma->vm_flags & VM_NO_KHUGEPAGED);
+}
+
+/*
+ * If mmap_sem temporarily dropped, revalidate vma
+ * before taking mmap_sem.
+ * 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 *vma;
+ unsigned long hstart, hend;
+
+ if (unlikely(khugepaged_test_exit(mm)))
+ return SCAN_ANY_PROCESS;
+
+ 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))
+ 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_sem 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)
+{
+ pte_t pteval;
+ int swapped_in = 0, ret = 0;
+ struct fault_env fe = {
+ .vma = vma,
+ .address = address,
+ .flags = FAULT_FLAG_ALLOW_RETRY,
+ .pmd = pmd,
+ };
+
+ fe.pte = pte_offset_map(pmd, address);
+ for (; fe.address < address + HPAGE_PMD_NR*PAGE_SIZE;
+ fe.pte++, fe.address += PAGE_SIZE) {
+ pteval = *fe.pte;
+ if (!is_swap_pte(pteval))
+ continue;
+ swapped_in++;
+ ret = do_swap_page(&fe, pteval);
+ /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
+ if (ret & VM_FAULT_RETRY) {
+ down_read(&mm->mmap_sem);
+ /* vma is no longer available, don't continue to swapin */
+ if (hugepage_vma_revalidate(mm, address))
+ return false;
+ /* check if the pmd is still valid */
+ if (mm_find_pmd(mm, address) != pmd)
+ return false;
+ }
+ if (ret & VM_FAULT_ERROR) {
+ trace_mm_collapse_huge_page_swapin(mm, swapped_in, 0);
+ return false;
+ }
+ /* pte is unmapped now, we need to map it */
+ fe.pte = pte_offset_map(pmd, fe.address);
+ }
+ fe.pte--;
+ pte_unmap(fe.pte);
+ trace_mm_collapse_huge_page_swapin(mm, swapped_in, 1);
+ return true;
+}
+
+static void collapse_huge_page(struct mm_struct *mm,
+ unsigned long address,
+ struct page **hpage,
+ struct vm_area_struct *vma,
+ int node)
+{
+ 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 mem_cgroup *memcg;
+ unsigned long mmun_start; /* For mmu_notifiers */
+ unsigned long mmun_end; /* For mmu_notifiers */
+ gfp_t gfp;
+
+ VM_BUG_ON(address & ~HPAGE_PMD_MASK);
+
+ /* Only allocate from the target node */
+ gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_OTHER_NODE | __GFP_THISNODE;
+
+ /* release the mmap_sem read lock. */
+ new_page = khugepaged_alloc_page(hpage, gfp, mm, address, node);
+ if (!new_page) {
+ result = SCAN_ALLOC_HUGE_PAGE_FAIL;
+ goto out_nolock;
+ }
+
+ if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
+ result = SCAN_CGROUP_CHARGE_FAIL;
+ goto out_nolock;
+ }
+
+ down_read(&mm->mmap_sem);
+ result = hugepage_vma_revalidate(mm, address);
+ if (result) {
+ mem_cgroup_cancel_charge(new_page, memcg, true);
+ up_read(&mm->mmap_sem);
+ goto out_nolock;
+ }
+
+ pmd = mm_find_pmd(mm, address);
+ if (!pmd) {
+ result = SCAN_PMD_NULL;
+ mem_cgroup_cancel_charge(new_page, memcg, true);
+ up_read(&mm->mmap_sem);
+ goto out_nolock;
+ }
+
+ /*
+ * __collapse_huge_page_swapin always returns with mmap_sem locked.
+ * If it fails, release mmap_sem and jump directly out.
+ * Continuing to collapse causes inconsistency.
+ */
+ if (!__collapse_huge_page_swapin(mm, vma, address, pmd)) {
+ mem_cgroup_cancel_charge(new_page, memcg, true);
+ up_read(&mm->mmap_sem);
+ goto out_nolock;
+ }
+
+ up_read(&mm->mmap_sem);
+ /*
+ * 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.
+ */
+ down_write(&mm->mmap_sem);
+ result = hugepage_vma_revalidate(mm, address);
+ 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);
+
+ pte = pte_offset_map(pmd, address);
+ pte_ptl = pte_lockptr(mm, pmd);
+
+ mmun_start = address;
+ mmun_end = address + HPAGE_PMD_SIZE;
+ mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
+ pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
+ /*
+ * After this gup_fast can't run anymore. This also 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.
+ */
+ _pmd = pmdp_collapse_flush(vma, address, pmd);
+ spin_unlock(pmd_ptl);
+ mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+
+ spin_lock(pte_ptl);
+ isolated = __collapse_huge_page_isolate(vma, address, pte);
+ 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);
+ 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);
+ mem_cgroup_commit_charge(new_page, memcg, false, true);
+ lru_cache_add_active_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:
+ up_write(&mm->mmap_sem);
+out_nolock:
+ trace_mm_collapse_huge_page(mm, isolated, result);
+ return;
+out:
+ mem_cgroup_cancel_charge(new_page, memcg, true);
+ 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, none_or_zero = 0, result = 0;
+ struct page *page = NULL;
+ unsigned long _address;
+ spinlock_t *ptl;
+ int node = NUMA_NO_NODE, unmapped = 0;
+ bool writable = false, referenced = 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) {
+ 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_write(pteval))
+ writable = true;
+
+ page = vm_normal_page(vma, _address, pteval);
+ if (unlikely(!page)) {
+ result = SCAN_PAGE_NULL;
+ goto out_unmap;
+ }
+
+ /* TODO: teach khugepaged to collapse THP mapped with pte */
+ if (PageCompound(page)) {
+ result = SCAN_PAGE_COMPOUND;
+ goto out_unmap;
+ }
+
+ /*
+ * 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;
+ }
+
+ /*
+ * cannot use mapcount: can't collapse if there's a gup pin.
+ * The page must only be referenced by the scanned process
+ * and page swap cache.
+ */
+ if (page_count(page) != 1 + !!PageSwapCache(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 = true;
+ }
+ if (writable) {
+ if (referenced) {
+ result = SCAN_SUCCEED;
+ ret = 1;
+ } else {
+ result = SCAN_NO_REFERENCED_PAGE;
+ }
+ } else {
+ result = SCAN_PAGE_RO;
+ }
+out_unmap:
+ pte_unmap_unlock(pte, ptl);
+ if (ret) {
+ node = khugepaged_find_target_node();
+ /* collapse_huge_page will return with the mmap_sem released */
+ collapse_huge_page(mm, address, hpage, vma, node);
+ }
+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;
+
+ VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&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);
+ }
+}
+
+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);
+ VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&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);
+
+ mm = mm_slot->mm;
+ down_read(&mm->mmap_sem);
+ if (unlikely(khugepaged_test_exit(mm)))
+ vma = NULL;
+ else
+ 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)) {
+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);
+
+ 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);
+ 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_sem so break loop */
+ goto breakouterloop_mmap_sem;
+ if (progress >= pages)
+ goto breakouterloop;
+ }
+ }
+breakouterloop:
+ up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
+breakouterloop_mmap_sem:
+
+ 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 */
+
+ 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)
+ 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)
+{
+ static struct task_struct *khugepaged_thread __read_mostly;
+ static DEFINE_MUTEX(khugepaged_mutex);
+ 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;
+}