// SPDX-License-Identifier: GPL-2.0

  #include <linux/init.h>

  #include <linux/memblock.h>

  #include <linux/fs.h>
  #include <linux/sysfs.h>
  #include <linux/kobject.h>

  #include <linux/memory_hotplug.h>

  #include <linux/mm.h>
  #include <linux/mmzone.h>
  #include <linux/pagemap.h>
  #include <linux/rmap.h>
  #include <linux/mmu_notifier.h>
  #include <linux/page_ext.h>
  #include <linux/page_idle.h>
  
  #define BITMAP_CHUNK_SIZE	sizeof(u64)
  #define BITMAP_CHUNK_BITS	(BITMAP_CHUNK_SIZE * BITS_PER_BYTE)
  
  /*
   * Idle page tracking only considers user memory pages, for other types of
   * pages the idle flag is always unset and an attempt to set it is silently
   * ignored.
   *
   * We treat a page as a user memory page if it is on an LRU list, because it is
   * always safe to pass such a page to rmap_walk(), which is essential for idle
   * page tracking. With such an indicator of user pages we can skip isolated
   * pages, but since there are not usually many of them, it will hardly affect
   * the overall result.
   *
   * This function tries to get a user memory page by pfn as described above.
   */
  static struct page *page_idle_get_page(unsigned long pfn)
  {

  	struct page *page = pfn_to_online_page(pfn);

  	pg_data_t *pgdat;

  	if (!page || !PageLRU(page) ||
  	    !get_page_unless_zero(page))
  		return NULL;

  	pgdat = page_pgdat(page);
  	spin_lock_irq(&pgdat->lru_lock);

  	if (unlikely(!PageLRU(page))) {
  		put_page(page);
  		page = NULL;
  	}

  	spin_unlock_irq(&pgdat->lru_lock);

  	return page;
  }

  static bool page_idle_clear_pte_refs_one(struct page *page,

  					struct vm_area_struct *vma,
  					unsigned long addr, void *arg)
  {

  	struct page_vma_mapped_walk pvmw = {
  		.page = page,
  		.vma = vma,
  		.address = addr,
  	};

  	bool referenced = false;

  	while (page_vma_mapped_walk(&pvmw)) {
  		addr = pvmw.address;
  		if (pvmw.pte) {

  			/*
  			 * For PTE-mapped THP, one sub page is referenced,
  			 * the whole THP is referenced.
  			 */
  			if (ptep_clear_young_notify(vma, addr, pvmw.pte))
  				referenced = true;

  		} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {

  			if (pmdp_clear_young_notify(vma, addr, pvmw.pmd))
  				referenced = true;

  		} else {
  			/* unexpected pmd-mapped page? */
  			WARN_ON_ONCE(1);
  		}

  	}

  	if (referenced) {
  		clear_page_idle(page);
  		/*
  		 * We cleared the referenced bit in a mapping to this page. To
  		 * avoid interference with page reclaim, mark it young so that
  		 * page_referenced() will return > 0.
  		 */
  		set_page_young(page);
  	}

  	return true;

  }
  
  static void page_idle_clear_pte_refs(struct page *page)
  {
  	/*
  	 * Since rwc.arg is unused, rwc is effectively immutable, so we
  	 * can make it static const to save some cycles and stack.
  	 */
  	static const struct rmap_walk_control rwc = {
  		.rmap_one = page_idle_clear_pte_refs_one,
  		.anon_lock = page_lock_anon_vma_read,
  	};
  	bool need_lock;
  
  	if (!page_mapped(page) ||
  	    !page_rmapping(page))
  		return;
  
  	need_lock = !PageAnon(page) || PageKsm(page);
  	if (need_lock && !trylock_page(page))
  		return;
  
  	rmap_walk(page, (struct rmap_walk_control *)&rwc);
  
  	if (need_lock)
  		unlock_page(page);
  }
  
  static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj,
  				     struct bin_attribute *attr, char *buf,
  				     loff_t pos, size_t count)
  {
  	u64 *out = (u64 *)buf;
  	struct page *page;
  	unsigned long pfn, end_pfn;
  	int bit;
  
  	if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
  		return -EINVAL;
  
  	pfn = pos * BITS_PER_BYTE;
  	if (pfn >= max_pfn)
  		return 0;
  
  	end_pfn = pfn + count * BITS_PER_BYTE;
  	if (end_pfn > max_pfn)

  		end_pfn = max_pfn;

  
  	for (; pfn < end_pfn; pfn++) {
  		bit = pfn % BITMAP_CHUNK_BITS;
  		if (!bit)
  			*out = 0ULL;
  		page = page_idle_get_page(pfn);
  		if (page) {
  			if (page_is_idle(page)) {
  				/*
  				 * The page might have been referenced via a
  				 * pte, in which case it is not idle. Clear
  				 * refs and recheck.
  				 */
  				page_idle_clear_pte_refs(page);
  				if (page_is_idle(page))
  					*out |= 1ULL << bit;
  			}
  			put_page(page);
  		}
  		if (bit == BITMAP_CHUNK_BITS - 1)
  			out++;
  		cond_resched();
  	}
  	return (char *)out - buf;
  }
  
  static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj,
  				      struct bin_attribute *attr, char *buf,
  				      loff_t pos, size_t count)
  {
  	const u64 *in = (u64 *)buf;
  	struct page *page;
  	unsigned long pfn, end_pfn;
  	int bit;
  
  	if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
  		return -EINVAL;
  
  	pfn = pos * BITS_PER_BYTE;
  	if (pfn >= max_pfn)
  		return -ENXIO;
  
  	end_pfn = pfn + count * BITS_PER_BYTE;
  	if (end_pfn > max_pfn)

  		end_pfn = max_pfn;

  
  	for (; pfn < end_pfn; pfn++) {
  		bit = pfn % BITMAP_CHUNK_BITS;
  		if ((*in >> bit) & 1) {
  			page = page_idle_get_page(pfn);
  			if (page) {
  				page_idle_clear_pte_refs(page);
  				set_page_idle(page);
  				put_page(page);
  			}
  		}
  		if (bit == BITMAP_CHUNK_BITS - 1)
  			in++;
  		cond_resched();
  	}
  	return (char *)in - buf;
  }
  
  static struct bin_attribute page_idle_bitmap_attr =

  		__BIN_ATTR(bitmap, 0600,

  			   page_idle_bitmap_read, page_idle_bitmap_write, 0);
  
  static struct bin_attribute *page_idle_bin_attrs[] = {
  	&page_idle_bitmap_attr,
  	NULL,
  };

  static const struct attribute_group page_idle_attr_group = {

  	.bin_attrs = page_idle_bin_attrs,
  	.name = "page_idle",
  };
  
  #ifndef CONFIG_64BIT
  static bool need_page_idle(void)
  {
  	return true;
  }
  struct page_ext_operations page_idle_ops = {
  	.need = need_page_idle,
  };
  #endif
  
  static int __init page_idle_init(void)
  {
  	int err;
  
  	err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
  	if (err) {
  		pr_err("page_idle: register sysfs failed
  ");
  		return err;
  	}
  	return 0;
  }
  subsys_initcall(page_idle_init);