/*
 * mm/rmap.c - physical to virtual reverse mappings
 *
 * Copyright 2001, Rik van Riel <riel@conectiva.com.br>
 * Released under the General Public License (GPL).
 *
 * Simple, low overhead reverse mapping scheme.
 * Please try to keep this thing as modular as possible.
 *
 * Provides methods for unmapping each kind of mapped page:
 * the anon methods track anonymous pages, and
 * the file methods track pages belonging to an inode.
 *
 * Original design by Rik van Riel <riel@conectiva.com.br> 2001
 * File methods by Dave McCracken <dmccr@us.ibm.com> 2003, 2004
 * Anonymous methods by Andrea Arcangeli <andrea@suse.de> 2004
 * Contributions by Hugh Dickins 2003, 2004
 */


#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/ksm.h>
#include <linux/rmap.h>
#include <linux/rcupdate.h>
#include <linux/export.h>
#include <linux/memcontrol.h>
#include <linux/mmu_notifier.h>
#include <linux/migrate.h>
#include <linux/hugetlb.h>

#include <asm/tlbflush.h>

#include "internal.h"

static struct kmem_cache *anon_vma_cachep;
static struct kmem_cache *anon_vma_chain_cachep;

static inline struct anon_vma *anon_vma_alloc(void)
{
	struct anon_vma *anon_vma;

	anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
	if (anon_vma) {
		atomic_set(&anon_vma->refcount, 1);
		anon_vma->root = anon_vma;
	}

	return anon_vma;
}

static inline void anon_vma_free(struct anon_vma *anon_vma)
{
	VM_BUG_ON(atomic_read(&anon_vma->refcount));

	/*
	 * Synchronize against page_lock_anon_vma_read() such that
	 * we can safely hold the lock without the anon_vma getting
	 * freed.
	 *
	 * Relies on the full mb implied by the atomic_dec_and_test() from
	 * put_anon_vma() against the acquire barrier implied by
	 * down_read_trylock() from page_lock_anon_vma_read(). This orders:
	 *
	 * page_lock_anon_vma_read()	VS	put_anon_vma()
	 *   down_read_trylock()		  atomic_dec_and_test()
	 *   LOCK				  MB
	 *   atomic_read()			  rwsem_is_locked()
	 *
	 * LOCK should suffice since the actual taking of the lock must
	 * happen _before_ what follows.
	 */
	might_sleep();
	if (mutex_is_locked(&anon_vma->root->mutex)) {
		anon_vma_lock(anon_vma);
		anon_vma_unlock(anon_vma);
	}

	kmem_cache_free(anon_vma_cachep, anon_vma);
}

static inline struct anon_vma_chain *anon_vma_chain_alloc(gfp_t gfp)
{
	return kmem_cache_alloc(anon_vma_chain_cachep, gfp);
}

static void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)
{
	kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain);
}

static void anon_vma_chain_link(struct vm_area_struct *vma,
				struct anon_vma_chain *avc,
				struct anon_vma *anon_vma)
{
	avc->vma = vma;
	avc->anon_vma = anon_vma;
	list_add(&avc->same_vma, &vma->anon_vma_chain);

	list_add_tail(&avc->same_anon_vma, &anon_vma->head);
}

int anon_vma_prepare(struct vm_area_struct *vma)
{
	struct anon_vma *anon_vma = vma->anon_vma;
	struct anon_vma_chain *avc;

	might_sleep();
	if (unlikely(!anon_vma)) {
		struct mm_struct *mm = vma->vm_mm;
		struct anon_vma *allocated;

		avc = anon_vma_chain_alloc(GFP_KERNEL);
		if (!avc)
			goto out_enomem;

		anon_vma = find_mergeable_anon_vma(vma);
		allocated = NULL;
		if (!anon_vma) {
			anon_vma = anon_vma_alloc();
			if (unlikely(!anon_vma))
				goto out_enomem_free_avc;
			allocated = anon_vma;
		}

		anon_vma_lock(anon_vma);
		
		spin_lock(&mm->page_table_lock);
		if (likely(!vma->anon_vma)) {
			vma->anon_vma = anon_vma;
			anon_vma_chain_link(vma, avc, anon_vma);
			allocated = NULL;
			avc = NULL;
		}
		spin_unlock(&mm->page_table_lock);
		anon_vma_unlock(anon_vma);

		if (unlikely(allocated))
			put_anon_vma(allocated);
		if (unlikely(avc))
			anon_vma_chain_free(avc);
	}
	return 0;

 out_enomem_free_avc:
	anon_vma_chain_free(avc);
 out_enomem:
	return -ENOMEM;
}

static inline struct anon_vma *lock_anon_vma_root(struct anon_vma *root, struct anon_vma *anon_vma)
{
	struct anon_vma *new_root = anon_vma->root;
	if (new_root != root) {
		if (WARN_ON_ONCE(root))
			mutex_unlock(&root->mutex);
		root = new_root;
		mutex_lock(&root->mutex);
	}
	return root;
}

static inline void unlock_anon_vma_root(struct anon_vma *root)
{
	if (root)
		mutex_unlock(&root->mutex);
}

int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
{
	struct anon_vma_chain *avc, *pavc;
	struct anon_vma *root = NULL;

	list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
		struct anon_vma *anon_vma;

		avc = anon_vma_chain_alloc(GFP_NOWAIT | __GFP_NOWARN);
		if (unlikely(!avc)) {
			unlock_anon_vma_root(root);
			root = NULL;
			avc = anon_vma_chain_alloc(GFP_KERNEL);
			if (!avc)
				goto enomem_failure;
		}
		anon_vma = pavc->anon_vma;
		root = lock_anon_vma_root(root, anon_vma);
		anon_vma_chain_link(dst, avc, anon_vma);
	}
	unlock_anon_vma_root(root);
	return 0;

 enomem_failure:
	unlink_anon_vmas(dst);
	return -ENOMEM;
}

void anon_vma_moveto_tail(struct vm_area_struct *dst)
{
	struct anon_vma_chain *pavc;
	struct anon_vma *root = NULL;

	list_for_each_entry_reverse(pavc, &dst->anon_vma_chain, same_vma) {
		struct anon_vma *anon_vma = pavc->anon_vma;
		VM_BUG_ON(pavc->vma != dst);
		root = lock_anon_vma_root(root, anon_vma);
		list_del(&pavc->same_anon_vma);
		list_add_tail(&pavc->same_anon_vma, &anon_vma->head);
	}
	unlock_anon_vma_root(root);
}

int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
{
	struct anon_vma_chain *avc;
	struct anon_vma *anon_vma;

	
	if (!pvma->anon_vma)
		return 0;

	if (anon_vma_clone(vma, pvma))
		return -ENOMEM;

	
	anon_vma = anon_vma_alloc();
	if (!anon_vma)
		goto out_error;
	avc = anon_vma_chain_alloc(GFP_KERNEL);
	if (!avc)
		goto out_error_free_anon_vma;

	anon_vma->root = pvma->anon_vma->root;
	get_anon_vma(anon_vma->root);
	
	vma->anon_vma = anon_vma;
	anon_vma_lock(anon_vma);
	anon_vma_chain_link(vma, avc, anon_vma);
	anon_vma_unlock(anon_vma);

	return 0;

 out_error_free_anon_vma:
	put_anon_vma(anon_vma);
 out_error:
	unlink_anon_vmas(vma);
	return -ENOMEM;
}

void unlink_anon_vmas(struct vm_area_struct *vma)
{
	struct anon_vma_chain *avc, *next;
	struct anon_vma *root = NULL;

	list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
		struct anon_vma *anon_vma = avc->anon_vma;

		root = lock_anon_vma_root(root, anon_vma);
		list_del(&avc->same_anon_vma);

		if (list_empty(&anon_vma->head))
			continue;

		list_del(&avc->same_vma);
		anon_vma_chain_free(avc);
	}
	unlock_anon_vma_root(root);

	list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
		struct anon_vma *anon_vma = avc->anon_vma;

		put_anon_vma(anon_vma);

		list_del(&avc->same_vma);
		anon_vma_chain_free(avc);
	}
}

static void anon_vma_ctor(void *data)
{
	struct anon_vma *anon_vma = data;

	mutex_init(&anon_vma->mutex);
	atomic_set(&anon_vma->refcount, 0);
	INIT_LIST_HEAD(&anon_vma->head);
}

void __init anon_vma_init(void)
{
	anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
			0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor);
	anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, SLAB_PANIC);
}

struct anon_vma *page_get_anon_vma(struct page *page)
{
	struct anon_vma *anon_vma = NULL;
	unsigned long anon_mapping;

	rcu_read_lock();
	anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
	if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
		goto out;
	if (!page_mapped(page))
		goto out;

	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
	if (!atomic_inc_not_zero(&anon_vma->refcount)) {
		anon_vma = NULL;
		goto out;
	}

	if (!page_mapped(page)) {
		rcu_read_unlock();
		put_anon_vma(anon_vma);
		return NULL;
	}
out:
	rcu_read_unlock();

	return anon_vma;
}

struct anon_vma *page_lock_anon_vma(struct page *page)
{
	struct anon_vma *anon_vma = NULL;
	struct anon_vma *root_anon_vma;
	unsigned long anon_mapping;

	rcu_read_lock();
	anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
	if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
		goto out;
	if (!page_mapped(page))
		goto out;

	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
	root_anon_vma = ACCESS_ONCE(anon_vma->root);
	if (mutex_trylock(&root_anon_vma->mutex)) {
		if (!page_mapped(page)) {
			mutex_unlock(&root_anon_vma->mutex);
			anon_vma = NULL;
		}
		goto out;
	}

	
	if (!atomic_inc_not_zero(&anon_vma->refcount)) {
		anon_vma = NULL;
		goto out;
	}

	if (!page_mapped(page)) {
		rcu_read_unlock();
		put_anon_vma(anon_vma);
		return NULL;
	}

	
	rcu_read_unlock();
	anon_vma_lock(anon_vma);

	if (atomic_dec_and_test(&anon_vma->refcount)) {
		anon_vma_unlock(anon_vma);
		__put_anon_vma(anon_vma);
		anon_vma = NULL;
	}

	return anon_vma;

out:
	rcu_read_unlock();
	return anon_vma;
}

void page_unlock_anon_vma(struct anon_vma *anon_vma)
{
	anon_vma_unlock(anon_vma);
}

inline unsigned long
vma_address(struct page *page, struct vm_area_struct *vma)
{
	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
	unsigned long address;

	if (unlikely(is_vm_hugetlb_page(vma)))
		pgoff = page->index << huge_page_order(page_hstate(page));
	address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
	if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
		
		return -EFAULT;
	}
	return address;
}

unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
{
	if (PageAnon(page)) {
		struct anon_vma *page__anon_vma = page_anon_vma(page);
		if (!vma->anon_vma || !page__anon_vma ||
		    vma->anon_vma->root != page__anon_vma->root)
			return -EFAULT;
	} else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
		if (!vma->vm_file ||
		    vma->vm_file->f_mapping != page->mapping)
			return -EFAULT;
	} else
		return -EFAULT;
	return vma_address(page, vma);
}

pte_t *__page_check_address(struct page *page, struct mm_struct *mm,
			  unsigned long address, spinlock_t **ptlp, int sync)
{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;
	spinlock_t *ptl;

	if (unlikely(PageHuge(page))) {
		pte = huge_pte_offset(mm, address);
		ptl = &mm->page_table_lock;
		goto check;
	}

	pgd = pgd_offset(mm, address);
	if (!pgd_present(*pgd))
		return NULL;

	pud = pud_offset(pgd, address);
	if (!pud_present(*pud))
		return NULL;

	pmd = pmd_offset(pud, address);
	if (!pmd_present(*pmd))
		return NULL;
	if (pmd_trans_huge(*pmd))
		return NULL;

	pte = pte_offset_map(pmd, address);
	
	if (!sync && !pte_present(*pte)) {
		pte_unmap(pte);
		return NULL;
	}

	ptl = pte_lockptr(mm, pmd);
check:
	spin_lock(ptl);
	if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) {
		*ptlp = ptl;
		return pte;
	}
	pte_unmap_unlock(pte, ptl);
	return NULL;
}

int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
{
	unsigned long address;
	pte_t *pte;
	spinlock_t *ptl;

	address = vma_address(page, vma);
	if (address == -EFAULT)		
		return 0;
	pte = page_check_address(page, vma->vm_mm, address, &ptl, 1);
	if (!pte)			
		return 0;
	pte_unmap_unlock(pte, ptl);

	return 1;
}

int page_referenced_one(struct page *page, struct vm_area_struct *vma,
			unsigned long address, unsigned int *mapcount,
			unsigned long *vm_flags)
{
	struct mm_struct *mm = vma->vm_mm;
	int referenced = 0;

	if (unlikely(PageTransHuge(page))) {
		pmd_t *pmd;

		spin_lock(&mm->page_table_lock);
		pmd = page_check_address_pmd(page, mm, address,
					     PAGE_CHECK_ADDRESS_PMD_FLAG);
		if (!pmd) {
			spin_unlock(&mm->page_table_lock);
			goto out;
		}

		if (vma->vm_flags & VM_LOCKED) {
			spin_unlock(&mm->page_table_lock);
			*mapcount = 0;	
			*vm_flags |= VM_LOCKED;
			goto out;
		}

		
		if (pmdp_clear_flush_young_notify(vma, address, pmd))
			referenced++;
		spin_unlock(&mm->page_table_lock);
	} else {
		pte_t *pte;
		spinlock_t *ptl;

		pte = page_check_address(page, mm, address, &ptl, 0);
		if (!pte)
			goto out;

		if (vma->vm_flags & VM_LOCKED) {
			pte_unmap_unlock(pte, ptl);
			*mapcount = 0;	
			*vm_flags |= VM_LOCKED;
			goto out;
		}

		if (ptep_clear_flush_young_notify(vma, address, pte)) {
			if (likely(!VM_SequentialReadHint(vma)))
				referenced++;
		}
		pte_unmap_unlock(pte, ptl);
	}

	(*mapcount)--;

	if (referenced)
		*vm_flags |= vma->vm_flags;
out:
	return referenced;
}

static int page_referenced_anon(struct page *page,
				struct mem_cgroup *memcg,
				unsigned long *vm_flags)
{
	unsigned int mapcount;
	struct anon_vma *anon_vma;
	struct anon_vma_chain *avc;
	int referenced = 0;

	anon_vma = page_lock_anon_vma(page);
	if (!anon_vma)
		return referenced;

	mapcount = page_mapcount(page);
	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
		struct vm_area_struct *vma = avc->vma;
		unsigned long address = vma_address(page, vma);
		if (address == -EFAULT)
			continue;
		if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
			continue;
		referenced += page_referenced_one(page, vma, address,
						  &mapcount, vm_flags);
		if (!mapcount)
			break;
	}

	page_unlock_anon_vma(anon_vma);
	return referenced;
}

static int page_referenced_file(struct page *page,
				struct mem_cgroup *memcg,
				unsigned long *vm_flags)
{
	unsigned int mapcount;
	struct address_space *mapping = page->mapping;
	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
	struct vm_area_struct *vma;
	struct prio_tree_iter iter;
	int referenced = 0;

	BUG_ON(PageAnon(page));

	BUG_ON(!PageLocked(page));

	mutex_lock(&mapping->i_mmap_mutex);

	mapcount = page_mapcount(page);

	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
		unsigned long address = vma_address(page, vma);
		if (address == -EFAULT)
			continue;
		if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
			continue;
		referenced += page_referenced_one(page, vma, address,
						  &mapcount, vm_flags);
		if (!mapcount)
			break;
	}

	mutex_unlock(&mapping->i_mmap_mutex);
	return referenced;
}

int page_referenced(struct page *page,
		    int is_locked,
		    struct mem_cgroup *memcg,
		    unsigned long *vm_flags)
{
	int referenced = 0;
	int we_locked = 0;

	*vm_flags = 0;
	if (page_mapped(page) && page_rmapping(page)) {
		if (!is_locked && (!PageAnon(page) || PageKsm(page))) {
			we_locked = trylock_page(page);
			if (!we_locked) {
				referenced++;
				goto out;
			}
		}
		if (unlikely(PageKsm(page)))
			referenced += page_referenced_ksm(page, memcg,
								vm_flags);
		else if (PageAnon(page))
			referenced += page_referenced_anon(page, memcg,
								vm_flags);
		else if (page->mapping)
			referenced += page_referenced_file(page, memcg,
								vm_flags);
		if (we_locked)
			unlock_page(page);

		if (page_test_and_clear_young(page_to_pfn(page)))
			referenced++;
	}
out:
	return referenced;
}

static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
			    unsigned long address)
{
	struct mm_struct *mm = vma->vm_mm;
	pte_t *pte;
	spinlock_t *ptl;
	int ret = 0;

	pte = page_check_address(page, mm, address, &ptl, 1);
	if (!pte)
		goto out;

	if (pte_dirty(*pte) || pte_write(*pte)) {
		pte_t entry;

		flush_cache_page(vma, address, pte_pfn(*pte));
		entry = ptep_clear_flush_notify(vma, address, pte);
		entry = pte_wrprotect(entry);
		entry = pte_mkclean(entry);
		set_pte_at(mm, address, pte, entry);
		ret = 1;
	}

	pte_unmap_unlock(pte, ptl);
out:
	return ret;
}

static int page_mkclean_file(struct address_space *mapping, struct page *page)
{
	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
	struct vm_area_struct *vma;
	struct prio_tree_iter iter;
	int ret = 0;

	BUG_ON(PageAnon(page));

	mutex_lock(&mapping->i_mmap_mutex);
	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
		if (vma->vm_flags & VM_SHARED) {
			unsigned long address = vma_address(page, vma);
			if (address == -EFAULT)
				continue;
			ret += page_mkclean_one(page, vma, address);
		}
	}
	mutex_unlock(&mapping->i_mmap_mutex);
	return ret;
}

int page_mkclean(struct page *page)
{
	int ret = 0;

	BUG_ON(!PageLocked(page));

	if (page_mapped(page)) {
		struct address_space *mapping = page_mapping(page);
		if (mapping) {
			ret = page_mkclean_file(mapping, page);
			if (page_test_and_clear_dirty(page_to_pfn(page), 1))
				ret = 1;
		}
	}

	return ret;
}
EXPORT_SYMBOL_GPL(page_mkclean);

void page_move_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address)
{
	struct anon_vma *anon_vma = vma->anon_vma;

	VM_BUG_ON(!PageLocked(page));
	VM_BUG_ON(!anon_vma);
	VM_BUG_ON(page->index != linear_page_index(vma, address));

	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
	page->mapping = (struct address_space *) anon_vma;
}

static void __page_set_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address, int exclusive)
{
	struct anon_vma *anon_vma = vma->anon_vma;

	BUG_ON(!anon_vma);

	if (PageAnon(page))
		return;

	if (!exclusive)
		anon_vma = anon_vma->root;

	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
	page->mapping = (struct address_space *) anon_vma;
	page->index = linear_page_index(vma, address);
}

static void __page_check_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address)
{
#ifdef CONFIG_DEBUG_VM
	BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root);
	BUG_ON(page->index != linear_page_index(vma, address));
#endif
}

void page_add_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address)
{
	do_page_add_anon_rmap(page, vma, address, 0);
}

void do_page_add_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address, int exclusive)
{
	int first = atomic_inc_and_test(&page->_mapcount);
	if (first) {
		if (!PageTransHuge(page))
			__inc_zone_page_state(page, NR_ANON_PAGES);
		else
			__inc_zone_page_state(page,
					      NR_ANON_TRANSPARENT_HUGEPAGES);
	}
	if (unlikely(PageKsm(page)))
		return;

	VM_BUG_ON(!PageLocked(page));
	
	if (first)
		__page_set_anon_rmap(page, vma, address, exclusive);
	else
		__page_check_anon_rmap(page, vma, address);
}

void page_add_new_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address)
{
	VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
	SetPageSwapBacked(page);
	atomic_set(&page->_mapcount, 0); 
	if (!PageTransHuge(page))
		__inc_zone_page_state(page, NR_ANON_PAGES);
	else
		__inc_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
	__page_set_anon_rmap(page, vma, address, 1);
	if (page_evictable(page, vma))
		lru_cache_add_lru(page, LRU_ACTIVE_ANON);
	else
		add_page_to_unevictable_list(page);
}

void page_add_file_rmap(struct page *page)
{
	bool locked;
	unsigned long flags;

	mem_cgroup_begin_update_page_stat(page, &locked, &flags);
	if (atomic_inc_and_test(&page->_mapcount)) {
		__inc_zone_page_state(page, NR_FILE_MAPPED);
		mem_cgroup_inc_page_stat(page, MEMCG_NR_FILE_MAPPED);
	}
	mem_cgroup_end_update_page_stat(page, &locked, &flags);
}

void page_remove_rmap(struct page *page)
{
	bool anon = PageAnon(page);
	bool locked;
	unsigned long flags;

	if (!anon)
		mem_cgroup_begin_update_page_stat(page, &locked, &flags);

	
	if (!atomic_add_negative(-1, &page->_mapcount))
		goto out;

	/*
	 * Now that the last pte has gone, s390 must transfer dirty
	 * flag from storage key to struct page.  We can usually skip
	 * this if the page is anon, so about to be freed; but perhaps
	 * not if it's in swapcache - there might be another pte slot
	 * containing the swap entry, but page not yet written to swap.
	 */
	if ((!anon || PageSwapCache(page)) &&
	    page_test_and_clear_dirty(page_to_pfn(page), 1))
		set_page_dirty(page);
	if (unlikely(PageHuge(page)))
		goto out;
	if (anon) {
		mem_cgroup_uncharge_page(page);
		if (!PageTransHuge(page))
			__dec_zone_page_state(page, NR_ANON_PAGES);
		else
			__dec_zone_page_state(page,
					      NR_ANON_TRANSPARENT_HUGEPAGES);
	} else {
		__dec_zone_page_state(page, NR_FILE_MAPPED);
		mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED);
	}
out:
	if (!anon)
		mem_cgroup_end_update_page_stat(page, &locked, &flags);
}

int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
		     unsigned long address, enum ttu_flags flags)
{
	struct mm_struct *mm = vma->vm_mm;
	pte_t *pte;
	pte_t pteval;
	spinlock_t *ptl;
	int ret = SWAP_AGAIN;

	pte = page_check_address(page, mm, address, &ptl, 0);
	if (!pte)
		goto out;

	if (!(flags & TTU_IGNORE_MLOCK)) {
		if (vma->vm_flags & VM_LOCKED)
			goto out_mlock;

		if (TTU_ACTION(flags) == TTU_MUNLOCK)
			goto out_unmap;
	}
	if (!(flags & TTU_IGNORE_ACCESS)) {
		if (ptep_clear_flush_young_notify(vma, address, pte)) {
			ret = SWAP_FAIL;
			goto out_unmap;
		}
  	}

	
	flush_cache_page(vma, address, page_to_pfn(page));
	pteval = ptep_clear_flush_notify(vma, address, pte);

	
	if (pte_dirty(pteval))
		set_page_dirty(page);

	
	update_hiwater_rss(mm);

	if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) {
		if (PageAnon(page))
			dec_mm_counter(mm, MM_ANONPAGES);
		else
			dec_mm_counter(mm, MM_FILEPAGES);
		set_pte_at(mm, address, pte,
				swp_entry_to_pte(make_hwpoison_entry(page)));
	} else if (PageAnon(page)) {
		swp_entry_t entry = { .val = page_private(page) };

		if (PageSwapCache(page)) {
			if (swap_duplicate(entry) < 0) {
				set_pte_at(mm, address, pte, pteval);
				ret = SWAP_FAIL;
				goto out_unmap;
			}
			if (list_empty(&mm->mmlist)) {
				spin_lock(&mmlist_lock);
				if (list_empty(&mm->mmlist))
					list_add(&mm->mmlist, &init_mm.mmlist);
				spin_unlock(&mmlist_lock);
			}
			dec_mm_counter(mm, MM_ANONPAGES);
			inc_mm_counter(mm, MM_SWAPENTS);
		} else if (IS_ENABLED(CONFIG_MIGRATION)) {
			BUG_ON(TTU_ACTION(flags) != TTU_MIGRATION);
			entry = make_migration_entry(page, pte_write(pteval));
		}
		set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
		BUG_ON(pte_file(*pte));
	} else if (IS_ENABLED(CONFIG_MIGRATION) &&
		   (TTU_ACTION(flags) == TTU_MIGRATION)) {
		
		swp_entry_t entry;
		entry = make_migration_entry(page, pte_write(pteval));
		set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
	} else
		dec_mm_counter(mm, MM_FILEPAGES);

	page_remove_rmap(page);
	page_cache_release(page);

out_unmap:
	pte_unmap_unlock(pte, ptl);
out:
	return ret;

out_mlock:
	pte_unmap_unlock(pte, ptl);


	if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
		if (vma->vm_flags & VM_LOCKED) {
			mlock_vma_page(page);
			ret = SWAP_MLOCK;
		}
		up_read(&vma->vm_mm->mmap_sem);
	}
	return ret;
}

#define CLUSTER_SIZE	min(32*PAGE_SIZE, PMD_SIZE)
#define CLUSTER_MASK	(~(CLUSTER_SIZE - 1))

static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
		struct vm_area_struct *vma, struct page *check_page)
{
	struct mm_struct *mm = vma->vm_mm;
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;
	pte_t pteval;
	spinlock_t *ptl;
	struct page *page;
	unsigned long address;
	unsigned long end;
	int ret = SWAP_AGAIN;
	int locked_vma = 0;

	address = (vma->vm_start + cursor) & CLUSTER_MASK;
	end = address + CLUSTER_SIZE;
	if (address < vma->vm_start)
		address = vma->vm_start;
	if (end > vma->vm_end)
		end = vma->vm_end;

	pgd = pgd_offset(mm, address);
	if (!pgd_present(*pgd))
		return ret;

	pud = pud_offset(pgd, address);
	if (!pud_present(*pud))
		return ret;

	pmd = pmd_offset(pud, address);
	if (!pmd_present(*pmd))
		return ret;

	if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
		locked_vma = (vma->vm_flags & VM_LOCKED);
		if (!locked_vma)
			up_read(&vma->vm_mm->mmap_sem); 
	}

	pte = pte_offset_map_lock(mm, pmd, address, &ptl);

	
	update_hiwater_rss(mm);

	for (; address < end; pte++, address += PAGE_SIZE) {
		if (!pte_present(*pte))
			continue;
		page = vm_normal_page(vma, address, *pte);
		BUG_ON(!page || PageAnon(page));

		if (locked_vma) {
			if (page == check_page) {
				/* we know we have check_page locked */
				mlock_vma_page(page);
				ret = SWAP_MLOCK;
			} else if (trylock_page(page)) {
				/*
				 * If we can lock the page, perform mlock.
				 * Otherwise leave the page alone, it will be
				 * eventually encountered again later.
				 */
				mlock_vma_page(page);
				unlock_page(page);
			}
			continue;	/* don't unmap */
		}

		if (ptep_clear_flush_young_notify(vma, address, pte))
			continue;

		
		flush_cache_page(vma, address, pte_pfn(*pte));
		pteval = ptep_clear_flush_notify(vma, address, pte);

		
		if (page->index != linear_page_index(vma, address))
			set_pte_at(mm, address, pte, pgoff_to_pte(page->index));

		
		if (pte_dirty(pteval))
			set_page_dirty(page);

		page_remove_rmap(page);
		page_cache_release(page);
		dec_mm_counter(mm, MM_FILEPAGES);
		(*mapcount)--;
	}
	pte_unmap_unlock(pte - 1, ptl);
	if (locked_vma)
		up_read(&vma->vm_mm->mmap_sem);
	return ret;
}

bool is_vma_temporary_stack(struct vm_area_struct *vma)
{
	int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);

	if (!maybe_stack)
		return false;

	if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) ==
						VM_STACK_INCOMPLETE_SETUP)
		return true;

	return false;
}

static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
{
	struct anon_vma *anon_vma;
	struct anon_vma_chain *avc;
	int ret = SWAP_AGAIN;

	anon_vma = page_lock_anon_vma(page);
	if (!anon_vma)
		return ret;

	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
		struct vm_area_struct *vma = avc->vma;
		unsigned long address;

		if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION) &&
				is_vma_temporary_stack(vma))
			continue;

		address = vma_address(page, vma);
		if (address == -EFAULT)
			continue;
		ret = try_to_unmap_one(page, vma, address, flags);
		if (ret != SWAP_AGAIN || !page_mapped(page))
			break;
	}

	page_unlock_anon_vma(anon_vma);
	return ret;
}

static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
{
	struct address_space *mapping = page->mapping;
	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
	struct vm_area_struct *vma;
	struct prio_tree_iter iter;
	int ret = SWAP_AGAIN;
	unsigned long cursor;
	unsigned long max_nl_cursor = 0;
	unsigned long max_nl_size = 0;
	unsigned int mapcount;

	mutex_lock(&mapping->i_mmap_mutex);
	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
		unsigned long address = vma_address(page, vma);
		if (address == -EFAULT)
			continue;
		ret = try_to_unmap_one(page, vma, address, flags);
		if (ret != SWAP_AGAIN || !page_mapped(page))
			goto out;
	}

	if (list_empty(&mapping->i_mmap_nonlinear))
		goto out;

	if (TTU_ACTION(flags) == TTU_MUNLOCK)
		goto out;

	list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
						shared.vm_set.list) {
		cursor = (unsigned long) vma->vm_private_data;
		if (cursor > max_nl_cursor)
			max_nl_cursor = cursor;
		cursor = vma->vm_end - vma->vm_start;
		if (cursor > max_nl_size)
			max_nl_size = cursor;
	}

	if (max_nl_size == 0) {	
		ret = SWAP_FAIL;
		goto out;
	}

	mapcount = page_mapcount(page);
	if (!mapcount)
		goto out;
	cond_resched();

	max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK;
	if (max_nl_cursor == 0)
		max_nl_cursor = CLUSTER_SIZE;

	do {
		list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
						shared.vm_set.list) {
			cursor = (unsigned long) vma->vm_private_data;
			while ( cursor < max_nl_cursor &&
				cursor < vma->vm_end - vma->vm_start) {
				if (try_to_unmap_cluster(cursor, &mapcount,
						vma, page) == SWAP_MLOCK)
					ret = SWAP_MLOCK;
				cursor += CLUSTER_SIZE;
				vma->vm_private_data = (void *) cursor;
				if ((int)mapcount <= 0)
					goto out;
			}
			vma->vm_private_data = (void *) max_nl_cursor;
		}
		cond_resched();
		max_nl_cursor += CLUSTER_SIZE;
	} while (max_nl_cursor <= max_nl_size);

	list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
		vma->vm_private_data = NULL;
out:
	mutex_unlock(&mapping->i_mmap_mutex);
	return ret;
}

int try_to_unmap(struct page *page, enum ttu_flags flags)
{
	int ret;

	BUG_ON(!PageLocked(page));
	VM_BUG_ON(!PageHuge(page) && PageTransHuge(page));

	if (unlikely(PageKsm(page)))
		ret = try_to_unmap_ksm(page, flags);
	else if (PageAnon(page))
		ret = try_to_unmap_anon(page, flags);
	else
		ret = try_to_unmap_file(page, flags);
	if (ret != SWAP_MLOCK && !page_mapped(page))
		ret = SWAP_SUCCESS;
	return ret;
}

int try_to_munlock(struct page *page)
{
	VM_BUG_ON(!PageLocked(page) || PageLRU(page));

	if (unlikely(PageKsm(page)))
		return try_to_unmap_ksm(page, TTU_MUNLOCK);
	else if (PageAnon(page))
		return try_to_unmap_anon(page, TTU_MUNLOCK);
	else
		return try_to_unmap_file(page, TTU_MUNLOCK);
}

void __put_anon_vma(struct anon_vma *anon_vma)
{
	struct anon_vma *root = anon_vma->root;

	anon_vma_free(anon_vma);
	if (root != anon_vma && atomic_dec_and_test(&root->refcount))
		anon_vma_free(root);
}

#ifdef CONFIG_MIGRATION
static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *,
		struct vm_area_struct *, unsigned long, void *), void *arg)
{
	struct anon_vma *anon_vma;
	struct anon_vma_chain *avc;
	int ret = SWAP_AGAIN;

	anon_vma = page_anon_vma(page);
	if (!anon_vma)
		return ret;
	anon_vma_lock(anon_vma);
	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
		struct vm_area_struct *vma = avc->vma;
		unsigned long address = vma_address(page, vma);
		if (address == -EFAULT)
			continue;
		ret = rmap_one(page, vma, address, arg);
		if (ret != SWAP_AGAIN)
			break;
	}
	anon_vma_unlock(anon_vma);
	return ret;
}

static int rmap_walk_file(struct page *page, int (*rmap_one)(struct page *,
		struct vm_area_struct *, unsigned long, void *), void *arg)
{
	struct address_space *mapping = page->mapping;
	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
	struct vm_area_struct *vma;
	struct prio_tree_iter iter;
	int ret = SWAP_AGAIN;

	if (!mapping)
		return ret;
	mutex_lock(&mapping->i_mmap_mutex);
	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
		unsigned long address = vma_address(page, vma);
		if (address == -EFAULT)
			continue;
		ret = rmap_one(page, vma, address, arg);
		if (ret != SWAP_AGAIN)
			break;
	}
	mutex_unlock(&mapping->i_mmap_mutex);
	return ret;
}

int rmap_walk(struct page *page, int (*rmap_one)(struct page *,
		struct vm_area_struct *, unsigned long, void *), void *arg)
{
	VM_BUG_ON(!PageLocked(page));

	if (unlikely(PageKsm(page)))
		return rmap_walk_ksm(page, rmap_one, arg);
	else if (PageAnon(page))
		return rmap_walk_anon(page, rmap_one, arg);
	else
		return rmap_walk_file(page, rmap_one, arg);
}
#endif 

#ifdef CONFIG_HUGETLB_PAGE
static void __hugepage_set_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address, int exclusive)
{
	struct anon_vma *anon_vma = vma->anon_vma;

	BUG_ON(!anon_vma);

	if (PageAnon(page))
		return;
	if (!exclusive)
		anon_vma = anon_vma->root;

	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
	page->mapping = (struct address_space *) anon_vma;
	page->index = linear_page_index(vma, address);
}

void hugepage_add_anon_rmap(struct page *page,
			    struct vm_area_struct *vma, unsigned long address)
{
	struct anon_vma *anon_vma = vma->anon_vma;
	int first;

	BUG_ON(!PageLocked(page));
	BUG_ON(!anon_vma);
	
	first = atomic_inc_and_test(&page->_mapcount);
	if (first)
		__hugepage_set_anon_rmap(page, vma, address, 0);
}

void hugepage_add_new_anon_rmap(struct page *page,
			struct vm_area_struct *vma, unsigned long address)
{
	BUG_ON(address < vma->vm_start || address >= vma->vm_end);
	atomic_set(&page->_mapcount, 0);
	__hugepage_set_anon_rmap(page, vma, address, 1);
}
#endif