text: // SPDX-License-Identifier: GPL-2.0-only
  /*
   *  linux/mm/swap.c
   *
   *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   */
  
  /*
   * This file contains the default values for the operation of the
   * Linux VM subsystem. Fine-tuning documentation can be found in
   * Documentation/admin-guide/sysctl/vm.rst.
   * Started 18.12.91
   * Swap aging added 23.2.95, Stephen Tweedie.
   * Buffermem limits added 12.3.98, Rik van Riel.
   */
  
  #include <linux/mm.h>
  #include <linux/sched.h>
  #include <linux/kernel_stat.h>
  #include <linux/swap.h>
  #include <linux/mman.h>
  #include <linux/pagemap.h>
  #include <linux/pagevec.h>
  #include <linux/init.h>
  #include <linux/export.h>
  #include <linux/mm_inline.h>
  #include <linux/percpu_counter.h>
  #include <linux/memremap.h>
  #include <linux/percpu.h>
  #include <linux/cpu.h>
  #include <linux/notifier.h>
  #include <linux/backing-dev.h>
  #include <linux/memcontrol.h>
  #include <linux/gfp.h>
  #include <linux/uio.h>
  #include <linux/hugetlb.h>
  #include <linux/page_idle.h>
  #include <linux/local_lock.h>
  
  #include "internal.h"
  
  #define CREATE_TRACE_POINTS
  #include <trace/events/pagemap.h>
  
  /* How many pages do we try to swap or page in/out together? */
  int page_cluster;
  
  /* Protecting only lru_rotate.pvec which requires disabling interrupts */
  struct lru_rotate {
  	local_lock_t lock;
  	struct pagevec pvec;
  };
  static DEFINE_PER_CPU(struct lru_rotate, lru_rotate) = {
  	.lock = INIT_LOCAL_LOCK(lock),
  };
  
  /*
   * The following struct pagevec are grouped together because they are protected
   * by disabling preemption (and interrupts remain enabled).
   */
  struct lru_pvecs {
  	local_lock_t lock;
  	struct pagevec lru_add;
  	struct pagevec lru_deactivate_file;
  	struct pagevec lru_deactivate;
  	struct pagevec lru_lazyfree;
  #ifdef CONFIG_SMP
  	struct pagevec activate_page;
  #endif
  };
  static DEFINE_PER_CPU(struct lru_pvecs, lru_pvecs) = {
  	.lock = INIT_LOCAL_LOCK(lock),
  };
  
  /*
   * This path almost never happens for VM activity - pages are normally
   * freed via pagevecs.  But it gets used by networking.
   */
  static void __page_cache_release(struct page *page)
  {
  	if (PageLRU(page)) {
  		pg_data_t *pgdat = page_pgdat(page);
  		struct lruvec *lruvec;
  		unsigned long flags;
  
  		spin_lock_irqsave(&pgdat->lru_lock, flags);
  		lruvec = mem_cgroup_page_lruvec(page, pgdat);
  		VM_BUG_ON_PAGE(!PageLRU(page), page);
  		__ClearPageLRU(page);
  		del_page_from_lru_list(page, lruvec, page_off_lru(page));
  		spin_unlock_irqrestore(&pgdat->lru_lock, flags);
  	}
  	__ClearPageWaiters(page);
  }
  
  static void __put_single_page(struct page *page)
  {
  	__page_cache_release(page);
  	mem_cgroup_uncharge(page);
  	free_unref_page(page);
  }
  
  static void __put_compound_page(struct page *page)
  {
  	/*
  	 * __page_cache_release() is supposed to be called for thp, not for
  	 * hugetlb. This is because hugetlb page does never have PageLRU set
  	 * (it's never listed to any LRU lists) and no memcg routines should
  	 * be called for hugetlb (it has a separate hugetlb_cgroup.)
  	 */
  	if (!PageHuge(page))
  		__page_cache_release(page);
  	destroy_compound_page(page);
  }
  
  void __put_page(struct page *page)
  {
  	if (is_zone_device_page(page)) {
  		put_dev_pagemap(page->pgmap);
  
  		/*
  		 * The page belongs to the device that created pgmap. Do
  		 * not return it to page allocator.
  		 */
  		return;
  	}
  
  	if (unlikely(PageCompound(page)))
  		__put_compound_page(page);
  	else
  		__put_single_page(page);
  }
  EXPORT_SYMBOL(__put_page);
  
  /**
   * put_pages_list() - release a list of pages
   * @pages: list of pages threaded on page->lru
   *
   * Release a list of pages which are strung together on page.lru.  Currently
   * used by read_cache_pages() and related error recovery code.
   */
  void put_pages_list(struct list_head *pages)
  {
  	while (!list_empty(pages)) {
  		struct page *victim;
  
  		victim = lru_to_page(pages);
  		list_del(&victim->lru);
  		put_page(victim);
  	}
  }
  EXPORT_SYMBOL(put_pages_list);
  
  /*
   * get_kernel_pages() - pin kernel pages in memory
   * @kiov:	An array of struct kvec structures
   * @nr_segs:	number of segments to pin
   * @write:	pinning for read/write, currently ignored
   * @pages:	array that receives pointers to the pages pinned.
   *		Should be at least nr_segs long.
   *
   * Returns number of pages pinned. This may be fewer than the number
   * requested. If nr_pages is 0 or negative, returns 0. If no pages
   * were pinned, returns -errno. Each page returned must be released
   * with a put_page() call when it is finished with.
   */
  int get_kernel_pages(const struct kvec *kiov, int nr_segs, int write,
  		struct page **pages)
  {
  	int seg;
  
  	for (seg = 0; seg < nr_segs; seg++) {
  		if (WARN_ON(kiov[seg].iov_len != PAGE_SIZE))
  			return seg;
  
  		pages[seg] = kmap_to_page(kiov[seg].iov_base);
  		get_page(pages[seg]);
  	}
  
  	return seg;
  }
  EXPORT_SYMBOL_GPL(get_kernel_pages);
  
  /*
   * get_kernel_page() - pin a kernel page in memory
   * @start:	starting kernel address
   * @write:	pinning for read/write, currently ignored
   * @pages:	array that receives pointer to the page pinned.
   *		Must be at least nr_segs long.
   *
   * Returns 1 if page is pinned. If the page was not pinned, returns
   * -errno. The page returned must be released with a put_page() call
   * when it is finished with.
   */
  int get_kernel_page(unsigned long start, int write, struct page **pages)
  {
  	const struct kvec kiov = {
  		.iov_base = (void *)start,
  		.iov_len = PAGE_SIZE
  	};
  
  	return get_kernel_pages(&kiov, 1, write, pages);
  }
  EXPORT_SYMBOL_GPL(get_kernel_page);
  
  static void pagevec_lru_move_fn(struct pagevec *pvec,
  	void (*move_fn)(struct page *page, struct lruvec *lruvec, void *arg),
  	void *arg)
  {
  	int i;
  	struct pglist_data *pgdat = NULL;
  	struct lruvec *lruvec;
  	unsigned long flags = 0;
  
  	for (i = 0; i < pagevec_count(pvec); i++) {
  		struct page *page = pvec->pages[i];
  		struct pglist_data *pagepgdat = page_pgdat(page);
  
  		if (pagepgdat != pgdat) {
  			if (pgdat)
  				spin_unlock_irqrestore(&pgdat->lru_lock, flags);
  			pgdat = pagepgdat;
  			spin_lock_irqsave(&pgdat->lru_lock, flags);
  		}
  
  		lruvec = mem_cgroup_page_lruvec(page, pgdat);
  		(*move_fn)(page, lruvec, arg);
  	}
  	if (pgdat)
  		spin_unlock_irqrestore(&pgdat->lru_lock, flags);
  	release_pages(pvec->pages, pvec->nr);
  	pagevec_reinit(pvec);
  }
  
  static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec,
  				 void *arg)
  {
  	int *pgmoved = arg;
  
  	if (PageLRU(page) && !PageUnevictable(page)) {
  		del_page_from_lru_list(page, lruvec, page_lru(page));
  		ClearPageActive(page);
  		add_page_to_lru_list_tail(page, lruvec, page_lru(page));
  		(*pgmoved) += hpage_nr_pages(page);
  	}
  }
  
  /*
   * pagevec_move_tail() must be called with IRQ disabled.
   * Otherwise this may cause nasty races.
   */
  static void pagevec_move_tail(struct pagevec *pvec)
  {
  	int pgmoved = 0;
  
  	pagevec_lru_move_fn(pvec, pagevec_move_tail_fn, &pgmoved);
  	__count_vm_events(PGROTATED, pgmoved);
  }
  
  /*
   * Writeback is about to end against a page which has been marked for immediate
   * reclaim.  If it still appears to be reclaimable, move it to the tail of the
   * inactive list.
   */
  void rotate_reclaimable_page(struct page *page)
  {
  	if (!PageLocked(page) && !PageDirty(page) &&
  	    !PageUnevictable(page) && PageLRU(page)) {
  		struct pagevec *pvec;
  		unsigned long flags;
  
  		get_page(page);
  		local_lock_irqsave(&lru_rotate.lock, flags);
  		pvec = this_cpu_ptr(&lru_rotate.pvec);
  		if (!pagevec_add(pvec, page) || PageCompound(page))
  			pagevec_move_tail(pvec);
  		local_unlock_irqrestore(&lru_rotate.lock, flags);
  	}
  }
  
  void lru_note_cost(struct lruvec *lruvec, bool file, unsigned int nr_pages)
  {
  	do {
  		unsigned long lrusize;
  
  		/* Record cost event */
  		if (file)
  			lruvec->file_cost += nr_pages;
  		else
  			lruvec->anon_cost += nr_pages;
  
  		/*
  		 * Decay previous events
  		 *
  		 * Because workloads change over time (and to avoid
  		 * overflow) we keep these statistics as a floating
  		 * average, which ends up weighing recent refaults
  		 * more than old ones.
  		 */
  		lrusize = lruvec_page_state(lruvec, NR_INACTIVE_ANON) +
  			  lruvec_page_state(lruvec, NR_ACTIVE_ANON) +
  			  lruvec_page_state(lruvec, NR_INACTIVE_FILE) +
  			  lruvec_page_state(lruvec, NR_ACTIVE_FILE);
  
  		if (lruvec->file_cost + lruvec->anon_cost > lrusize / 4) {
  			lruvec->file_cost /= 2;
  			lruvec->anon_cost /= 2;
  		}
  	} while ((lruvec = parent_lruvec(lruvec)));
  }
  
  void lru_note_cost_page(struct page *page)
  {
  	lru_note_cost(mem_cgroup_page_lruvec(page, page_pgdat(page)),
  		      page_is_file_lru(page), hpage_nr_pages(page));
  }
  
  static void __activate_page(struct page *page, struct lruvec *lruvec,
  			    void *arg)
  {
  	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
  		int lru = page_lru_base_type(page);
  		int nr_pages = hpage_nr_pages(page);
  
  		del_page_from_lru_list(page, lruvec, lru);
  		SetPageActive(page);
  		lru += LRU_ACTIVE;
  		add_page_to_lru_list(page, lruvec, lru);
  		trace_mm_lru_activate(page);
  
  		__count_vm_events(PGACTIVATE, nr_pages);
  		__count_memcg_events(lruvec_memcg(lruvec), PGACTIVATE,
  				     nr_pages);
  	}
  }
  
  #ifdef CONFIG_SMP
  static void activate_page_drain(int cpu)
  {
  	struct pagevec *pvec = &per_cpu(lru_pvecs.activate_page, cpu);
  
  	if (pagevec_count(pvec))
  		pagevec_lru_move_fn(pvec, __activate_page, NULL);
  }
  
  static bool need_activate_page_drain(int cpu)
  {
  	return pagevec_count(&per_cpu(lru_pvecs.activate_page, cpu)) != 0;
  }
  
  void activate_page(struct page *page)
  {
  	page = compound_head(page);
  	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
  		struct pagevec *pvec;
  
  		local_lock(&lru_pvecs.lock);
  		pvec = this_cpu_ptr(&lru_pvecs.activate_page);
  		get_page(page);
  		if (!pagevec_add(pvec, page) || PageCompound(page))
  			pagevec_lru_move_fn(pvec, __activate_page, NULL);
  		local_unlock(&lru_pvecs.lock);
  	}
  }
  
  #else
  static inline void activate_page_drain(int cpu)
  {
  }
  
  void activate_page(struct page *page)
  {
  	pg_data_t *pgdat = page_pgdat(page);
  
  	page = compound_head(page);
  	spin_lock_irq(&pgdat->lru_lock);
  	__activate_page(page, mem_cgroup_page_lruvec(page, pgdat), NULL);
  	spin_unlock_irq(&pgdat->lru_lock);
  }
  #endif
  
  static void __lru_cache_activate_page(struct page *page)
  {
  	struct pagevec *pvec;
  	int i;
  
  	local_lock(&lru_pvecs.lock);
  	pvec = this_cpu_ptr(&lru_pvecs.lru_add);
  
  	/*
  	 * Search backwards on the optimistic assumption that the page being
  	 * activated has just been added to this pagevec. Note that only
  	 * the local pagevec is examined as a !PageLRU page could be in the
  	 * process of being released, reclaimed, migrated or on a remote
  	 * pagevec that is currently being drained. Furthermore, marking
  	 * a remote pagevec's page PageActive potentially hits a race where
  	 * a page is marked PageActive just after it is added to the inactive
  	 * list causing accounting errors and BUG_ON checks to trigger.
  	 */
  	for (i = pagevec_count(pvec) - 1; i >= 0; i--) {
  		struct page *pagevec_page = pvec->pages[i];
  
  		if (pagevec_page == page) {
  			SetPageActive(page);
  			break;
  		}
  	}
  
  	local_unlock(&lru_pvecs.lock);
  }
  
  /*
   * Mark a page as having seen activity.
   *
   * inactive,unreferenced	->	inactive,referenced
   * inactive,referenced		->	active,unreferenced
   * active,unreferenced		->	active,referenced
   *
   * When a newly allocated page is not yet visible, so safe for non-atomic ops,
   * __SetPageReferenced(page) may be substituted for mark_page_accessed(page).
   */
  void mark_page_accessed(struct page *page)
  {
  	page = compound_head(page);
  
  	if (!PageReferenced(page)) {
  		SetPageReferenced(page);
  	} else if (PageUnevictable(page)) {
  		/*
  		 * Unevictable pages are on the "LRU_UNEVICTABLE" list. But,
  		 * this list is never rotated or maintained, so marking an
  		 * evictable page accessed has no effect.
  		 */
  	} else if (!PageActive(page)) {
  		/*
  		 * If the page is on the LRU, queue it for activation via
  		 * lru_pvecs.activate_page. Otherwise, assume the page is on a
  		 * pagevec, mark it active and it'll be moved to the active
  		 * LRU on the next drain.
  		 */
  		if (PageLRU(page))
  			activate_page(page);
  		else
  			__lru_cache_activate_page(page);
  		ClearPageReferenced(page);
  		workingset_activation(page);
  	}
  	if (page_is_idle(page))
  		clear_page_idle(page);
  }
  EXPORT_SYMBOL(mark_page_accessed);
  
  /**
   * lru_cache_add - add a page to a page list
   * @page: the page to be added to the LRU.
   *
   * Queue the page for addition to the LRU via pagevec. The decision on whether
   * to add the page to the [in]active [file|anon] list is deferred until the
   * pagevec is drained. This gives a chance for the caller of lru_cache_add()
   * have the page added to the active list using mark_page_accessed().
   */
  void lru_cache_add(struct page *page)
  {
  	struct pagevec *pvec;
  
  	VM_BUG_ON_PAGE(PageActive(page) && PageUnevictable(page), page);
  	VM_BUG_ON_PAGE(PageLRU(page), page);
  
  	get_page(page);
  	local_lock(&lru_pvecs.lock);
  	pvec = this_cpu_ptr(&lru_pvecs.lru_add);
  	if (!pagevec_add(pvec, page) || PageCompound(page))
  		__pagevec_lru_add(pvec);
  	local_unlock(&lru_pvecs.lock);
  }
  EXPORT_SYMBOL(lru_cache_add);
  
  /**
   * lru_cache_add_active_or_unevictable
   * @page:  the page to be added to LRU
   * @vma:   vma in which page is mapped for determining reclaimability
   *
   * Place @page on the active or unevictable LRU list, depending on its
   * evictability.  Note that if the page is not evictable, it goes
   * directly back onto it's zone's unevictable list, it does NOT use a
   * per cpu pagevec.
   */
  void lru_cache_add_active_or_unevictable(struct page *page,
  					 struct vm_area_struct *vma)
  {
  	VM_BUG_ON_PAGE(PageLRU(page), page);
  
  	if (likely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED))
  		SetPageActive(page);
  	else if (!TestSetPageMlocked(page)) {
  		/*
  		 * We use the irq-unsafe __mod_zone_page_stat because this
  		 * counter is not modified from interrupt context, and the pte
  		 * lock is held(spinlock), which implies preemption disabled.
  		 */
  		__mod_zone_page_state(page_zone(page), NR_MLOCK,
  				    hpage_nr_pages(page));
  		count_vm_event(UNEVICTABLE_PGMLOCKED);
  	}
  	lru_cache_add(page);
  }
  
  /*
   * If the page can not be invalidated, it is moved to the
   * inactive list to speed up its reclaim.  It is moved to the
   * head of the list, rather than the tail, to give the flusher
   * threads some time to write it out, as this is much more
   * effective than the single-page writeout from reclaim.
   *
   * If the page isn't page_mapped and dirty/writeback, the page
   * could reclaim asap using PG_reclaim.
   *
   * 1. active, mapped page -> none
   * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
   * 3. inactive, mapped page -> none
   * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
   * 5. inactive, clean -> inactive, tail
   * 6. Others -> none
   *
   * In 4, why it moves inactive's head, the VM expects the page would
   * be write it out by flusher threads as this is much more effective
   * than the single-page writeout from reclaim.
   */
  static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec,
  			      void *arg)
  {
  	int lru;
  	bool active;
  	int nr_pages = hpage_nr_pages(page);
  
  	if (!PageLRU(page))
  		return;
  
  	if (PageUnevictable(page))
  		return;
  
  	/* Some processes are using the page */
  	if (page_mapped(page))
  		return;
  
  	active = PageActive(page);
  	lru = page_lru_base_type(page);
  
  	del_page_from_lru_list(page, lruvec, lru + active);
  	ClearPageActive(page);
  	ClearPageReferenced(page);
  
  	if (PageWriteback(page) || PageDirty(page)) {
  		/*
  		 * PG_reclaim could be raced with end_page_writeback
  		 * It can make readahead confusing.  But race window
  		 * is _really_ small and  it's non-critical problem.
  		 */
  		add_page_to_lru_list(page, lruvec, lru);
  		SetPageReclaim(page);
  	} else {
  		/*
  		 * The page's writeback ends up during pagevec
  		 * We moves tha page into tail of inactive.
  		 */
  		add_page_to_lru_list_tail(page, lruvec, lru);
  		__count_vm_events(PGROTATED, nr_pages);
  	}
  
  	if (active) {
  		__count_vm_events(PGDEACTIVATE, nr_pages);
  		__count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE,
  				     nr_pages);
  	}
  }
  
  static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
  			    void *arg)
  {
  	if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
  		int lru = page_lru_base_type(page);
  		int nr_pages = hpage_nr_pages(page);
  
  		del_page_from_lru_list(page, lruvec, lru + LRU_ACTIVE);
  		ClearPageActive(page);
  		ClearPageReferenced(page);
  		add_page_to_lru_list(page, lruvec, lru);
  
  		__count_vm_events(PGDEACTIVATE, nr_pages);
  		__count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE,
  				     nr_pages);
  	}
  }
  
  static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
  			    void *arg)
  {
  	if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
  	    !PageSwapCache(page) && !PageUnevictable(page)) {
  		bool active = PageActive(page);
  		int nr_pages = hpage_nr_pages(page);
  
  		del_page_from_lru_list(page, lruvec,
  				       LRU_INACTIVE_ANON + active);
  		ClearPageActive(page);
  		ClearPageReferenced(page);
  		/*
  		 * Lazyfree pages are clean anonymous pages.  They have
  		 * PG_swapbacked flag cleared, to distinguish them from normal
  		 * anonymous pages
  		 */
  		ClearPageSwapBacked(page);
  		add_page_to_lru_list(page, lruvec, LRU_INACTIVE_FILE);
  
  		__count_vm_events(PGLAZYFREE, nr_pages);
  		__count_memcg_events(lruvec_memcg(lruvec), PGLAZYFREE,
  				     nr_pages);
  	}
  }
  
  /*
   * Drain pages out of the cpu's pagevecs.
   * Either "cpu" is the current CPU, and preemption has already been
   * disabled; or "cpu" is being hot-unplugged, and is already dead.
   */
  void lru_add_drain_cpu(int cpu)
  {
  	struct pagevec *pvec = &per_cpu(lru_pvecs.lru_add, cpu);
  
  	if (pagevec_count(pvec))
  		__pagevec_lru_add(pvec);
  
  	pvec = &per_cpu(lru_rotate.pvec, cpu);
  	if (pagevec_count(pvec)) {
  		unsigned long flags;
  
  		/* No harm done if a racing interrupt already did this */
  		local_lock_irqsave(&lru_rotate.lock, flags);
  		pagevec_move_tail(pvec);
  		local_unlock_irqrestore(&lru_rotate.lock, flags);
  	}
  
  	pvec = &per_cpu(lru_pvecs.lru_deactivate_file, cpu);
  	if (pagevec_count(pvec))
  		pagevec_lru_move_fn(pvec, lru_deactivate_file_fn, NULL);
  
  	pvec = &per_cpu(lru_pvecs.lru_deactivate, cpu);
  	if (pagevec_count(pvec))
  		pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
  
  	pvec = &per_cpu(lru_pvecs.lru_lazyfree, cpu);
  	if (pagevec_count(pvec))
  		pagevec_lru_move_fn(pvec, lru_lazyfree_fn, NULL);
  
  	activate_page_drain(cpu);
  }
  
  /**
   * deactivate_file_page - forcefully deactivate a file page
   * @page: page to deactivate
   *
   * This function hints the VM that @page is a good reclaim candidate,
   * for example if its invalidation fails due to the page being dirty
   * or under writeback.
   */
  void deactivate_file_page(struct page *page)
  {
  	/*
  	 * In a workload with many unevictable page such as mprotect,
  	 * unevictable page deactivation for accelerating reclaim is pointless.
  	 */
  	if (PageUnevictable(page))
  		return;
  
  	if (likely(get_page_unless_zero(page))) {
  		struct pagevec *pvec;
  
  		local_lock(&lru_pvecs.lock);
  		pvec = this_cpu_ptr(&lru_pvecs.lru_deactivate_file);
  
  		if (!pagevec_add(pvec, page) || PageCompound(page))
  			pagevec_lru_move_fn(pvec, lru_deactivate_file_fn, NULL);
  		local_unlock(&lru_pvecs.lock);
  	}
  }
  
  /*
   * deactivate_page - deactivate a page
   * @page: page to deactivate
   *
   * deactivate_page() moves @page to the inactive list if @page was on the active
   * list and was not an unevictable page.  This is done to accelerate the reclaim
   * of @page.
   */
  void deactivate_page(struct page *page)
  {
  	if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
  		struct pagevec *pvec;
  
  		local_lock(&lru_pvecs.lock);
  		pvec = this_cpu_ptr(&lru_pvecs.lru_deactivate);
  		get_page(page);
  		if (!pagevec_add(pvec, page) || PageCompound(page))
  			pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
  		local_unlock(&lru_pvecs.lock);
  	}
  }
  
  /**
   * mark_page_lazyfree - make an anon page lazyfree
   * @page: page to deactivate
   *
   * mark_page_lazyfree() moves @page to the inactive file list.
   * This is done to accelerate the reclaim of @page.
   */
  void mark_page_lazyfree(struct page *page)
  {
  	if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
  	    !PageSwapCache(page) && !PageUnevictable(page)) {
  		struct pagevec *pvec;
  
  		local_lock(&lru_pvecs.lock);
  		pvec = this_cpu_ptr(&lru_pvecs.lru_lazyfree);
  		get_page(page);
  		if (!pagevec_add(pvec, page) || PageCompound(page))
  			pagevec_lru_move_fn(pvec, lru_lazyfree_fn, NULL);
  		local_unlock(&lru_pvecs.lock);
  	}
  }
  
  void lru_add_drain(void)
  {
  	local_lock(&lru_pvecs.lock);
  	lru_add_drain_cpu(smp_processor_id());
  	local_unlock(&lru_pvecs.lock);
  }
  
  void lru_add_drain_cpu_zone(struct zone *zone)
  {
  	local_lock(&lru_pvecs.lock);
  	lru_add_drain_cpu(smp_processor_id());
  	drain_local_pages(zone);
  	local_unlock(&lru_pvecs.lock);
  }
  
  #ifdef CONFIG_SMP
  
  static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
  
  static void lru_add_drain_per_cpu(struct work_struct *dummy)
  {
  	lru_add_drain();
  }
  
  /*
   * Doesn't need any cpu hotplug locking because we do rely on per-cpu
   * kworkers being shut down before our page_alloc_cpu_dead callback is
   * executed on the offlined cpu.
   * Calling this function with cpu hotplug locks held can actually lead
   * to obscure indirect dependencies via WQ context.
   */
  void lru_add_drain_all(void)
  {
  	static seqcount_t seqcount = SEQCNT_ZERO(seqcount);
  	static DEFINE_MUTEX(lock);
  	static struct cpumask has_work;
  	int cpu, seq;
  
  	/*
  	 * Make sure nobody triggers this path before mm_percpu_wq is fully
  	 * initialized.
  	 */
  	if (WARN_ON(!mm_percpu_wq))
  		return;
  
  	seq = raw_read_seqcount_latch(&seqcount);
  
  	mutex_lock(&lock);
  
  	/*
  	 * Piggyback on drain started and finished while we waited for lock:
  	 * all pages pended at the time of our enter were drained from vectors.
  	 */
  	if (__read_seqcount_retry(&seqcount, seq))
  		goto done;
  
  	raw_write_seqcount_latch(&seqcount);
  
  	cpumask_clear(&has_work);
  
  	for_each_online_cpu(cpu) {
  		struct work_struct *work = &per_cpu(lru_add_drain_work, cpu);
  
  		if (pagevec_count(&per_cpu(lru_pvecs.lru_add, cpu)) ||
  		    pagevec_count(&per_cpu(lru_rotate.pvec, cpu)) ||
  		    pagevec_count(&per_cpu(lru_pvecs.lru_deactivate_file, cpu)) ||
  		    pagevec_count(&per_cpu(lru_pvecs.lru_deactivate, cpu)) ||
  		    pagevec_count(&per_cpu(lru_pvecs.lru_lazyfree, cpu)) ||
  		    need_activate_page_drain(cpu)) {
  			INIT_WORK(work, lru_add_drain_per_cpu);
  			queue_work_on(cpu, mm_percpu_wq, work);
  			cpumask_set_cpu(cpu, &has_work);
  		}
  	}
  
  	for_each_cpu(cpu, &has_work)
  		flush_work(&per_cpu(lru_add_drain_work, cpu));
  
  done:
  	mutex_unlock(&lock);
  }
  #else
  void lru_add_drain_all(void)
  {
  	lru_add_drain();
  }
  #endif
  
  /**
   * release_pages - batched put_page()
   * @pages: array of pages to release
   * @nr: number of pages
   *
   * Decrement the reference count on all the pages in @pages.  If it
   * fell to zero, remove the page from the LRU and free it.
   */
  void release_pages(struct page **pages, int nr)
  {
  	int i;
  	LIST_HEAD(pages_to_free);
  	struct pglist_data *locked_pgdat = NULL;
  	struct lruvec *lruvec;
  	unsigned long uninitialized_var(flags);
  	unsigned int uninitialized_var(lock_batch);
  
  	for (i = 0; i < nr; i++) {
  		struct page *page = pages[i];
  
  		/*
  		 * Make sure the IRQ-safe lock-holding time does not get
  		 * excessive with a continuous string of pages from the
  		 * same pgdat. The lock is held only if pgdat != NULL.
  		 */
  		if (locked_pgdat && ++lock_batch == SWAP_CLUSTER_MAX) {
  			spin_unlock_irqrestore(&locked_pgdat->lru_lock, flags);
  			locked_pgdat = NULL;
  		}
  
  		if (is_huge_zero_page(page))
  			continue;
  
  		if (is_zone_device_page(page)) {
  			if (locked_pgdat) {
  				spin_unlock_irqrestore(&locked_pgdat->lru_lock,
  						       flags);
  				locked_pgdat = NULL;
  			}
  			/*
  			 * ZONE_DEVICE pages that return 'false' from
  			 * put_devmap_managed_page() do not require special
  			 * processing, and instead, expect a call to
  			 * put_page_testzero().
  			 */
  			if (page_is_devmap_managed(page)) {
  				put_devmap_managed_page(page);
  				continue;
  			}
  		}
  
  		page = compound_head(page);
  		if (!put_page_testzero(page))
  			continue;
  
  		if (PageCompound(page)) {
  			if (locked_pgdat) {
  				spin_unlock_irqrestore(&locked_pgdat->lru_lock, flags);
  				locked_pgdat = NULL;
  			}
  			__put_compound_page(page);
  			continue;
  		}
  
  		if (PageLRU(page)) {
  			struct pglist_data *pgdat = page_pgdat(page);
  
  			if (pgdat != locked_pgdat) {
  				if (locked_pgdat)
  					spin_unlock_irqrestore(&locked_pgdat->lru_lock,
  									flags);
  				lock_batch = 0;
  				locked_pgdat = pgdat;
  				spin_lock_irqsave(&locked_pgdat->lru_lock, flags);
  			}
  
  			lruvec = mem_cgroup_page_lruvec(page, locked_pgdat);
  			VM_BUG_ON_PAGE(!PageLRU(page), page);
  			__ClearPageLRU(page);
  			del_page_from_lru_list(page, lruvec, page_off_lru(page));
  		}
  
  		/* Clear Active bit in case of parallel mark_page_accessed */
  		__ClearPageActive(page);
  		__ClearPageWaiters(page);
  
  		list_add(&page->lru, &pages_to_free);
  	}
  	if (locked_pgdat)
  		spin_unlock_irqrestore(&locked_pgdat->lru_lock, flags);
  
  	mem_cgroup_uncharge_list(&pages_to_free);
  	free_unref_page_list(&pages_to_free);
  }
  EXPORT_SYMBOL(release_pages);
  
  /*
   * The pages which we're about to release may be in the deferred lru-addition
   * queues.  That would prevent them from really being freed right now.  That's
   * OK from a correctness point of view but is inefficient - those pages may be
   * cache-warm and we want to give them back to the page allocator ASAP.
   *
   * So __pagevec_release() will drain those queues here.  __pagevec_lru_add()
   * and __pagevec_lru_add_active() call release_pages() directly to avoid
   * mutual recursion.
   */
  void __pagevec_release(struct pagevec *pvec)
  {
  	if (!pvec->percpu_pvec_drained) {
  		lru_add_drain();
  		pvec->percpu_pvec_drained = true;
  	}
  	release_pages(pvec->pages, pagevec_count(pvec));
  	pagevec_reinit(pvec);
  }
  EXPORT_SYMBOL(__pagevec_release);
  
  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
  /* used by __split_huge_page_refcount() */
  void lru_add_page_tail(struct page *page, struct page *page_tail,
  		       struct lruvec *lruvec, struct list_head *list)
  {
  	VM_BUG_ON_PAGE(!PageHead(page), page);
  	VM_BUG_ON_PAGE(PageCompound(page_tail), page);
  	VM_BUG_ON_PAGE(PageLRU(page_tail), page);
  	lockdep_assert_held(&lruvec_pgdat(lruvec)->lru_lock);
  
  	if (!list)
  		SetPageLRU(page_tail);
  
  	if (likely(PageLRU(page)))
  		list_add_tail(&page_tail->lru, &page->lru);
  	else if (list) {
  		/* page reclaim is reclaiming a huge page */
  		get_page(page_tail);
  		list_add_tail(&page_tail->lru, list);
  	} else {
  		/*
  		 * Head page has not yet been counted, as an hpage,
  		 * so we must account for each subpage individually.
  		 *
  		 * Put page_tail on the list at the correct position
  		 * so they all end up in order.
  		 */
  		add_page_to_lru_list_tail(page_tail, lruvec,
  					  page_lru(page_tail));
  	}
  }
  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
  
  static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
  				 void *arg)
  {
  	enum lru_list lru;
  	int was_unevictable = TestClearPageUnevictable(page);
  	int nr_pages = hpage_nr_pages(page);
  
  	VM_BUG_ON_PAGE(PageLRU(page), page);
  
  	/*
  	 * Page becomes evictable in two ways:
  	 * 1) Within LRU lock [munlock_vma_page() and __munlock_pagevec()].
  	 * 2) Before acquiring LRU lock to put the page to correct LRU and then
  	 *   a) do PageLRU check with lock [check_move_unevictable_pages]
  	 *   b) do PageLRU check before lock [clear_page_mlock]
  	 *
  	 * (1) & (2a) are ok as LRU lock will serialize them. For (2b), we need
  	 * following strict ordering:
  	 *
  	 * #0: __pagevec_lru_add_fn		#1: clear_page_mlock
  	 *
  	 * SetPageLRU()				TestClearPageMlocked()
  	 * smp_mb() // explicit ordering	// above provides strict
  	 *					// ordering
  	 * PageMlocked()			PageLRU()
  	 *
  	 *
  	 * if '#1' does not observe setting of PG_lru by '#0' and fails
  	 * isolation, the explicit barrier will make sure that page_evictable
  	 * check will put the page in correct LRU. Without smp_mb(), SetPageLRU
  	 * can be reordered after PageMlocked check and can make '#1' to fail
  	 * the isolation of the page whose Mlocked bit is cleared (#0 is also
  	 * looking at the same page) and the evictable page will be stranded
  	 * in an unevictable LRU.
  	 */
  	SetPageLRU(page);
  	smp_mb__after_atomic();
  
  	if (page_evictable(page)) {
  		lru = page_lru(page);
  		if (was_unevictable)
  			__count_vm_events(UNEVICTABLE_PGRESCUED, nr_pages);
  	} else {
  		lru = LRU_UNEVICTABLE;
  		ClearPageActive(page);
  		SetPageUnevictable(page);
  		if (!was_unevictable)
  			__count_vm_events(UNEVICTABLE_PGCULLED, nr_pages);
  	}
  
  	add_page_to_lru_list(page, lruvec, lru);
  	trace_mm_lru_insertion(page, lru);
  }
  
  /*
   * Add the passed pages to the LRU, then drop the caller's refcount
   * on them.  Reinitialises the caller's pagevec.
   */
  void __pagevec_lru_add(struct pagevec *pvec)
  {
  	pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn, NULL);
  }
  
  /**
   * pagevec_lookup_entries - gang pagecache lookup
   * @pvec:	Where the resulting entries are placed
   * @mapping:	The address_space to search
   * @start:	The starting entry index
   * @nr_entries:	The maximum number of pages
   * @indices:	The cache indices corresponding to the entries in @pvec
   *
   * pagevec_lookup_entries() will search for and return a group of up
   * to @nr_pages pages and shadow entries in the mapping.  All
   * entries are placed in @pvec.  pagevec_lookup_entries() takes a
   * reference against actual pages in @pvec.
   *
   * The search returns a group of mapping-contiguous entries with
   * ascending indexes.  There may be holes in the indices due to
   * not-present entries.
   *
   * Only one subpage of a Transparent Huge Page is returned in one call:
   * allowing truncate_inode_pages_range() to evict the whole THP without
   * cycling through a pagevec of extra references.
   *
   * pagevec_lookup_entries() returns the number of entries which were
   * found.
   */
  unsigned pagevec_lookup_entries(struct pagevec *pvec,
  				struct address_space *mapping,
  				pgoff_t start, unsigned nr_entries,
  				pgoff_t *indices)
  {
  	pvec->nr = find_get_entries(mapping, start, nr_entries,
  				    pvec->pages, indices);
  	return pagevec_count(pvec);
  }
  
  /**
   * pagevec_remove_exceptionals - pagevec exceptionals pruning
   * @pvec:	The pagevec to prune
   *
   * pagevec_lookup_entries() fills both pages and exceptional radix
   * tree entries into the pagevec.  This function prunes all
   * exceptionals from @pvec without leaving holes, so that it can be
   * passed on to page-only pagevec operations.
   */
  void pagevec_remove_exceptionals(struct pagevec *pvec)
  {
  	int i, j;
  
  	for (i = 0, j = 0; i < pagevec_count(pvec); i++) {
  		struct page *page = pvec->pages[i];
  		if (!xa_is_value(page))
  			pvec->pages[j++] = page;
  	}
  	pvec->nr = j;
  }
  
  /**
   * pagevec_lookup_range - gang pagecache lookup
   * @pvec:	Where the resulting pages are placed
   * @mapping:	The address_space to search
   * @start:	The starting page index
   * @end:	The final page index
   *
   * pagevec_lookup_range() will search for & return a group of up to PAGEVEC_SIZE
   * pages in the mapping starting from index @start and upto index @end
   * (inclusive).  The pages are placed in @pvec.  pagevec_lookup() takes a
   * reference against the pages in @pvec.
   *
   * The search returns a group of mapping-contiguous pages with ascending
   * indexes.  There may be holes in the indices due to not-present pages. We
   * also update @start to index the next page for the traversal.
   *
   * pagevec_lookup_range() returns the number of pages which were found. If this
   * number is smaller than PAGEVEC_SIZE, the end of specified range has been
   * reached.
   */
  unsigned pagevec_lookup_range(struct pagevec *pvec,
  		struct address_space *mapping, pgoff_t *start, pgoff_t end)
  {
  	pvec->nr = find_get_pages_range(mapping, start, end, PAGEVEC_SIZE,
  					pvec->pages);
  	return pagevec_count(pvec);
  }
  EXPORT_SYMBOL(pagevec_lookup_range);
  
  unsigned pagevec_lookup_range_tag(struct pagevec *pvec,
  		struct address_space *mapping, pgoff_t *index, pgoff_t end,
  		xa_mark_t tag)
  {
  	pvec->nr = find_get_pages_range_tag(mapping, index, end, tag,
  					PAGEVEC_SIZE, pvec->pages);
  	return pagevec_count(pvec);
  }
  EXPORT_SYMBOL(pagevec_lookup_range_tag);
  
  unsigned pagevec_lookup_range_nr_tag(struct pagevec *pvec,
  		struct address_space *mapping, pgoff_t *index, pgoff_t end,
  		xa_mark_t tag, unsigned max_pages)
  {
  	pvec->nr = find_get_pages_range_tag(mapping, index, end, tag,
  		min_t(unsigned int, max_pages, PAGEVEC_SIZE), pvec->pages);
  	return pagevec_count(pvec);
  }
  EXPORT_SYMBOL(pagevec_lookup_range_nr_tag);
  /*
   * Perform any setup for the swap system
   */
  void __init swap_setup(void)
  {
  	unsigned long megs = totalram_pages() >> (20 - PAGE_SHIFT);
  
  	/* Use a smaller cluster for small-memory machines */
  	if (megs < 16)
  		page_cluster = 2;
  	else
  		page_cluster = 3;
  	/*
  	 * Right now other parts of the system means that we
  	 * _really_ don't want to cluster much more
  	 */
  }
  
  #ifdef CONFIG_DEV_PAGEMAP_OPS
  void put_devmap_managed_page(struct page *page)
  {
  	int count;
  
  	if (WARN_ON_ONCE(!page_is_devmap_managed(page)))
  		return;
  
  	count = page_ref_dec_return(page);
  
  	/*
  	 * devmap page refcounts are 1-based, rather than 0-based: if
  	 * refcount is 1, then the page is free and the refcount is
  	 * stable because nobody holds a reference on the page.
  	 */
  	if (count == 1)
  		free_devmap_managed_page(page);
  	else if (!count)
  		__put_page(page);
  }
  EXPORT_SYMBOL(put_devmap_managed_page);
  #endif
  