text: // SPDX-License-Identifier: GPL-2.0
  #include <linux/mm.h>
  #include <linux/mmzone.h>
  #include <linux/page_reporting.h>
  #include <linux/gfp.h>
  #include <linux/export.h>
  #include <linux/delay.h>
  #include <linux/scatterlist.h>
  
  #include "page_reporting.h"
  #include "internal.h"
  
  #define PAGE_REPORTING_DELAY	(2 * HZ)
  static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
  
  enum {
  	PAGE_REPORTING_IDLE = 0,
  	PAGE_REPORTING_REQUESTED,
  	PAGE_REPORTING_ACTIVE
  };
  
  /* request page reporting */
  static void
  __page_reporting_request(struct page_reporting_dev_info *prdev)
  {
  	unsigned int state;
  
  	/* Check to see if we are in desired state */
  	state = atomic_read(&prdev->state);
  	if (state == PAGE_REPORTING_REQUESTED)
  		return;
  
  	/*
  	 *  If reporting is already active there is nothing we need to do.
  	 *  Test against 0 as that represents PAGE_REPORTING_IDLE.
  	 */
  	state = atomic_xchg(&prdev->state, PAGE_REPORTING_REQUESTED);
  	if (state != PAGE_REPORTING_IDLE)
  		return;
  
  	/*
  	 * Delay the start of work to allow a sizable queue to build. For
  	 * now we are limiting this to running no more than once every
  	 * couple of seconds.
  	 */
  	schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
  }
  
  /* notify prdev of free page reporting request */
  void __page_reporting_notify(void)
  {
  	struct page_reporting_dev_info *prdev;
  
  	/*
  	 * We use RCU to protect the pr_dev_info pointer. In almost all
  	 * cases this should be present, however in the unlikely case of
  	 * a shutdown this will be NULL and we should exit.
  	 */
  	rcu_read_lock();
  	prdev = rcu_dereference(pr_dev_info);
  	if (likely(prdev))
  		__page_reporting_request(prdev);
  
  	rcu_read_unlock();
  }
  
  static void
  page_reporting_drain(struct page_reporting_dev_info *prdev,
  		     struct scatterlist *sgl, unsigned int nents, bool reported)
  {
  	struct scatterlist *sg = sgl;
  
  	/*
  	 * Drain the now reported pages back into their respective
  	 * free lists/areas. We assume at least one page is populated.
  	 */
  	do {
  		struct page *page = sg_page(sg);
  		int mt = get_pageblock_migratetype(page);
  		unsigned int order = get_order(sg->length);
  
  		__putback_isolated_page(page, order, mt);
  
  		/* If the pages were not reported due to error skip flagging */
  		if (!reported)
  			continue;
  
  		/*
  		 * If page was not comingled with another page we can
  		 * consider the result to be "reported" since the page
  		 * hasn't been modified, otherwise we will need to
  		 * report on the new larger page when we make our way
  		 * up to that higher order.
  		 */
  		if (PageBuddy(page) && buddy_order(page) == order)
  			__SetPageReported(page);
  	} while ((sg = sg_next(sg)));
  
  	/* reinitialize scatterlist now that it is empty */
  	sg_init_table(sgl, nents);
  }
  
  /*
   * The page reporting cycle consists of 4 stages, fill, report, drain, and
   * idle. We will cycle through the first 3 stages until we cannot obtain a
   * full scatterlist of pages, in that case we will switch to idle.
   */
  static int
  page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
  		     unsigned int order, unsigned int mt,
  		     struct scatterlist *sgl, unsigned int *offset)
  {
  	struct free_area *area = &zone->free_area[order];
  	struct list_head *list = &area->free_list[mt];
  	unsigned int page_len = PAGE_SIZE << order;
  	struct page *page, *next;
  	long budget;
  	int err = 0;
  
  	/*
  	 * Perform early check, if free area is empty there is
  	 * nothing to process so we can skip this free_list.
  	 */
  	if (list_empty(list))
  		return err;
  
  	spin_lock_irq(&zone->lock);
  
  	/*
  	 * Limit how many calls we will be making to the page reporting
  	 * device for this list. By doing this we avoid processing any
  	 * given list for too long.
  	 *
  	 * The current value used allows us enough calls to process over a
  	 * sixteenth of the current list plus one additional call to handle
  	 * any pages that may have already been present from the previous
  	 * list processed. This should result in us reporting all pages on
  	 * an idle system in about 30 seconds.
  	 *
  	 * The division here should be cheap since PAGE_REPORTING_CAPACITY
  	 * should always be a power of 2.
  	 */
  	budget = DIV_ROUND_UP(area->nr_free, PAGE_REPORTING_CAPACITY * 16);
  
  	/* loop through free list adding unreported pages to sg list */
  	list_for_each_entry_safe(page, next, list, lru) {
  		/* We are going to skip over the reported pages. */
  		if (PageReported(page))
  			continue;
  
  		/*
  		 * If we fully consumed our budget then update our
  		 * state to indicate that we are requesting additional
  		 * processing and exit this list.
  		 */
  		if (budget < 0) {
  			atomic_set(&prdev->state, PAGE_REPORTING_REQUESTED);
  			next = page;
  			break;
  		}
  
  		/* Attempt to pull page from list and place in scatterlist */
  		if (*offset) {
  			if (!__isolate_free_page(page, order)) {
  				next = page;
  				break;
  			}
  
  			/* Add page to scatter list */
  			--(*offset);
  			sg_set_page(&sgl[*offset], page, page_len, 0);
  
  			continue;
  		}
  
  		/*
  		 * Make the first non-reported page in the free list
  		 * the new head of the free list before we release the
  		 * zone lock.
  		 */
  		if (!list_is_first(&page->lru, list))
  			list_rotate_to_front(&page->lru, list);
  
  		/* release lock before waiting on report processing */
  		spin_unlock_irq(&zone->lock);
  
  		/* begin processing pages in local list */
  		err = prdev->report(prdev, sgl, PAGE_REPORTING_CAPACITY);
  
  		/* reset offset since the full list was reported */
  		*offset = PAGE_REPORTING_CAPACITY;
  
  		/* update budget to reflect call to report function */
  		budget--;
  
  		/* reacquire zone lock and resume processing */
  		spin_lock_irq(&zone->lock);
  
  		/* flush reported pages from the sg list */
  		page_reporting_drain(prdev, sgl, PAGE_REPORTING_CAPACITY, !err);
  
  		/*
  		 * Reset next to first entry, the old next isn't valid
  		 * since we dropped the lock to report the pages
  		 */
  		next = list_first_entry(list, struct page, lru);
  
  		/* exit on error */
  		if (err)
  			break;
  	}
  
  	/* Rotate any leftover pages to the head of the freelist */
  	if (&next->lru != list && !list_is_first(&next->lru, list))
  		list_rotate_to_front(&next->lru, list);
  
  	spin_unlock_irq(&zone->lock);
  
  	return err;
  }
  
  static int
  page_reporting_process_zone(struct page_reporting_dev_info *prdev,
  			    struct scatterlist *sgl, struct zone *zone)
  {
  	unsigned int order, mt, leftover, offset = PAGE_REPORTING_CAPACITY;
  	unsigned long watermark;
  	int err = 0;
  
  	/* Generate minimum watermark to be able to guarantee progress */
  	watermark = low_wmark_pages(zone) +
  		    (PAGE_REPORTING_CAPACITY << PAGE_REPORTING_MIN_ORDER);
  
  	/*
  	 * Cancel request if insufficient free memory or if we failed
  	 * to allocate page reporting statistics for the zone.
  	 */
  	if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
  		return err;
  
  	/* Process each free list starting from lowest order/mt */
  	for (order = PAGE_REPORTING_MIN_ORDER; order < MAX_ORDER; order++) {
  		for (mt = 0; mt < MIGRATE_TYPES; mt++) {
  			/* We do not pull pages from the isolate free list */
  			if (is_migrate_isolate(mt))
  				continue;
  
  			err = page_reporting_cycle(prdev, zone, order, mt,
  						   sgl, &offset);
  			if (err)
  				return err;
  		}
  	}
  
  	/* report the leftover pages before going idle */
  	leftover = PAGE_REPORTING_CAPACITY - offset;
  	if (leftover) {
  		sgl = &sgl[offset];
  		err = prdev->report(prdev, sgl, leftover);
  
  		/* flush any remaining pages out from the last report */
  		spin_lock_irq(&zone->lock);
  		page_reporting_drain(prdev, sgl, leftover, !err);
  		spin_unlock_irq(&zone->lock);
  	}
  
  	return err;
  }
  
  static void page_reporting_process(struct work_struct *work)
  {
  	struct delayed_work *d_work = to_delayed_work(work);
  	struct page_reporting_dev_info *prdev =
  		container_of(d_work, struct page_reporting_dev_info, work);
  	int err = 0, state = PAGE_REPORTING_ACTIVE;
  	struct scatterlist *sgl;
  	struct zone *zone;
  
  	/*
  	 * Change the state to "Active" so that we can track if there is
  	 * anyone requests page reporting after we complete our pass. If
  	 * the state is not altered by the end of the pass we will switch
  	 * to idle and quit scheduling reporting runs.
  	 */
  	atomic_set(&prdev->state, state);
  
  	/* allocate scatterlist to store pages being reported on */
  	sgl = kmalloc_array(PAGE_REPORTING_CAPACITY, sizeof(*sgl), GFP_KERNEL);
  	if (!sgl)
  		goto err_out;
  
  	sg_init_table(sgl, PAGE_REPORTING_CAPACITY);
  
  	for_each_zone(zone) {
  		err = page_reporting_process_zone(prdev, sgl, zone);
  		if (err)
  			break;
  	}
  
  	kfree(sgl);
  err_out:
  	/*
  	 * If the state has reverted back to requested then there may be
  	 * additional pages to be processed. We will defer for 2s to allow
  	 * more pages to accumulate.
  	 */
  	state = atomic_cmpxchg(&prdev->state, state, PAGE_REPORTING_IDLE);
  	if (state == PAGE_REPORTING_REQUESTED)
  		schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
  }
  
  static DEFINE_MUTEX(page_reporting_mutex);
  DEFINE_STATIC_KEY_FALSE(page_reporting_enabled);
  
  int page_reporting_register(struct page_reporting_dev_info *prdev)
  {
  	int err = 0;
  
  	mutex_lock(&page_reporting_mutex);
  
  	/* nothing to do if already in use */
  	if (rcu_access_pointer(pr_dev_info)) {
  		err = -EBUSY;
  		goto err_out;
  	}
  
  	/* initialize state and work structures */
  	atomic_set(&prdev->state, PAGE_REPORTING_IDLE);
  	INIT_DELAYED_WORK(&prdev->work, &page_reporting_process);
  
  	/* Begin initial flush of zones */
  	__page_reporting_request(prdev);
  
  	/* Assign device to allow notifications */
  	rcu_assign_pointer(pr_dev_info, prdev);
  
  	/* enable page reporting notification */
  	if (!static_key_enabled(&page_reporting_enabled)) {
  		static_branch_enable(&page_reporting_enabled);
  		pr_info("Free page reporting enabled\n");
  	}
  err_out:
  	mutex_unlock(&page_reporting_mutex);
  
  	return err;
  }
  EXPORT_SYMBOL_GPL(page_reporting_register);
  
  void page_reporting_unregister(struct page_reporting_dev_info *prdev)
  {
  	mutex_lock(&page_reporting_mutex);
  
  	if (rcu_access_pointer(pr_dev_info) == prdev) {
  		/* Disable page reporting notification */
  		RCU_INIT_POINTER(pr_dev_info, NULL);
  		synchronize_rcu();
  
  		/* Flush any existing work, and lock it out */
  		cancel_delayed_work_sync(&prdev->work);
  	}
  
  	mutex_unlock(&page_reporting_mutex);
  }
  EXPORT_SYMBOL_GPL(page_reporting_unregister);
  