/*
   * linux/mm/compaction.c
   *
   * Memory compaction for the reduction of external fragmentation. Note that
   * this heavily depends upon page migration to do all the real heavy
   * lifting
   *
   * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
   */
  #include <linux/swap.h>
  #include <linux/migrate.h>
  #include <linux/compaction.h>
  #include <linux/mm_inline.h>
  #include <linux/backing-dev.h>

  #include <linux/sysctl.h>

  #include <linux/sysfs.h>

  #include "internal.h"

  #define CREATE_TRACE_POINTS
  #include <trace/events/compaction.h>

  /*
   * compact_control is used to track pages being migrated and the free pages
   * they are being migrated to during memory compaction. The free_pfn starts
   * at the end of a zone and migrate_pfn begins at the start. Movable pages
   * are moved to the end of a zone during a compaction run and the run
   * completes when free_pfn <= migrate_pfn
   */
  struct compact_control {
  	struct list_head freepages;	/* List of free pages to migrate to */
  	struct list_head migratepages;	/* List of pages being migrated */
  	unsigned long nr_freepages;	/* Number of isolated free pages */
  	unsigned long nr_migratepages;	/* Number of pages to migrate */
  	unsigned long free_pfn;		/* isolate_freepages search base */
  	unsigned long migrate_pfn;	/* isolate_migratepages search base */

  	bool sync;			/* Synchronous migration */

  
  	/* Account for isolated anon and file pages */
  	unsigned long nr_anon;
  	unsigned long nr_file;

  	unsigned int order;		/* order a direct compactor needs */
  	int migratetype;		/* MOVABLE, RECLAIMABLE etc */

  	struct zone *zone;

  
  	int compact_mode;

  };
  
  static unsigned long release_freepages(struct list_head *freelist)
  {
  	struct page *page, *next;
  	unsigned long count = 0;
  
  	list_for_each_entry_safe(page, next, freelist, lru) {
  		list_del(&page->lru);
  		__free_page(page);
  		count++;
  	}
  
  	return count;
  }
  
  /* Isolate free pages onto a private freelist. Must hold zone->lock */
  static unsigned long isolate_freepages_block(struct zone *zone,
  				unsigned long blockpfn,
  				struct list_head *freelist)
  {
  	unsigned long zone_end_pfn, end_pfn;

  	int nr_scanned = 0, total_isolated = 0;

  	struct page *cursor;
  
  	/* Get the last PFN we should scan for free pages at */
  	zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
  	end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);
  
  	/* Find the first usable PFN in the block to initialse page cursor */
  	for (; blockpfn < end_pfn; blockpfn++) {
  		if (pfn_valid_within(blockpfn))
  			break;
  	}
  	cursor = pfn_to_page(blockpfn);
  
  	/* Isolate free pages. This assumes the block is valid */
  	for (; blockpfn < end_pfn; blockpfn++, cursor++) {
  		int isolated, i;
  		struct page *page = cursor;
  
  		if (!pfn_valid_within(blockpfn))
  			continue;

  		nr_scanned++;

  
  		if (!PageBuddy(page))
  			continue;
  
  		/* Found a free page, break it into order-0 pages */
  		isolated = split_free_page(page);
  		total_isolated += isolated;
  		for (i = 0; i < isolated; i++) {
  			list_add(&page->lru, freelist);
  			page++;
  		}
  
  		/* If a page was split, advance to the end of it */
  		if (isolated) {
  			blockpfn += isolated - 1;
  			cursor += isolated - 1;
  		}
  	}

  	trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);

  	return total_isolated;
  }
  
  /* Returns true if the page is within a block suitable for migration to */
  static bool suitable_migration_target(struct page *page)
  {
  
  	int migratetype = get_pageblock_migratetype(page);
  
  	/* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
  	if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
  		return false;
  
  	/* If the page is a large free page, then allow migration */
  	if (PageBuddy(page) && page_order(page) >= pageblock_order)
  		return true;
  
  	/* If the block is MIGRATE_MOVABLE, allow migration */
  	if (migratetype == MIGRATE_MOVABLE)
  		return true;
  
  	/* Otherwise skip the block */
  	return false;
  }
  
  /*
   * Based on information in the current compact_control, find blocks
   * suitable for isolating free pages from and then isolate them.
   */
  static void isolate_freepages(struct zone *zone,
  				struct compact_control *cc)
  {
  	struct page *page;
  	unsigned long high_pfn, low_pfn, pfn;
  	unsigned long flags;
  	int nr_freepages = cc->nr_freepages;
  	struct list_head *freelist = &cc->freepages;
  
  	pfn = cc->free_pfn;
  	low_pfn = cc->migrate_pfn + pageblock_nr_pages;
  	high_pfn = low_pfn;
  
  	/*
  	 * Isolate free pages until enough are available to migrate the
  	 * pages on cc->migratepages. We stop searching if the migrate
  	 * and free page scanners meet or enough free pages are isolated.
  	 */
  	spin_lock_irqsave(&zone->lock, flags);
  	for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
  					pfn -= pageblock_nr_pages) {
  		unsigned long isolated;
  
  		if (!pfn_valid(pfn))
  			continue;
  
  		/*
  		 * Check for overlapping nodes/zones. It's possible on some
  		 * configurations to have a setup like
  		 * node0 node1 node0
  		 * i.e. it's possible that all pages within a zones range of
  		 * pages do not belong to a single zone.
  		 */
  		page = pfn_to_page(pfn);
  		if (page_zone(page) != zone)
  			continue;
  
  		/* Check the block is suitable for migration */
  		if (!suitable_migration_target(page))
  			continue;
  
  		/* Found a block suitable for isolating free pages from */
  		isolated = isolate_freepages_block(zone, pfn, freelist);
  		nr_freepages += isolated;
  
  		/*
  		 * Record the highest PFN we isolated pages from. When next
  		 * looking for free pages, the search will restart here as
  		 * page migration may have returned some pages to the allocator
  		 */
  		if (isolated)
  			high_pfn = max(high_pfn, pfn);
  	}
  	spin_unlock_irqrestore(&zone->lock, flags);
  
  	/* split_free_page does not map the pages */
  	list_for_each_entry(page, freelist, lru) {
  		arch_alloc_page(page, 0);
  		kernel_map_pages(page, 1, 1);
  	}
  
  	cc->free_pfn = high_pfn;
  	cc->nr_freepages = nr_freepages;
  }
  
  /* Update the number of anon and file isolated pages in the zone */
  static void acct_isolated(struct zone *zone, struct compact_control *cc)
  {
  	struct page *page;
  	unsigned int count[NR_LRU_LISTS] = { 0, };
  
  	list_for_each_entry(page, &cc->migratepages, lru) {
  		int lru = page_lru_base_type(page);
  		count[lru]++;
  	}
  
  	cc->nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
  	cc->nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
  	__mod_zone_page_state(zone, NR_ISOLATED_ANON, cc->nr_anon);
  	__mod_zone_page_state(zone, NR_ISOLATED_FILE, cc->nr_file);
  }
  
  /* Similar to reclaim, but different enough that they don't share logic */
  static bool too_many_isolated(struct zone *zone)
  {

  	unsigned long active, inactive, isolated;

  
  	inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
  					zone_page_state(zone, NR_INACTIVE_ANON);

  	active = zone_page_state(zone, NR_ACTIVE_FILE) +
  					zone_page_state(zone, NR_ACTIVE_ANON);

  	isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
  					zone_page_state(zone, NR_ISOLATED_ANON);

  	return isolated > (inactive + active) / 2;

  }
  
  /*
   * Isolate all pages that can be migrated from the block pointed to by
   * the migrate scanner within compact_control.
   */
  static unsigned long isolate_migratepages(struct zone *zone,
  					struct compact_control *cc)
  {
  	unsigned long low_pfn, end_pfn;

  	unsigned long last_pageblock_nr = 0, pageblock_nr;

  	unsigned long nr_scanned = 0, nr_isolated = 0;

  	struct list_head *migratelist = &cc->migratepages;
  
  	/* Do not scan outside zone boundaries */
  	low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
  
  	/* Only scan within a pageblock boundary */
  	end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
  
  	/* Do not cross the free scanner or scan within a memory hole */
  	if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
  		cc->migrate_pfn = end_pfn;
  		return 0;
  	}
  
  	/*
  	 * Ensure that there are not too many pages isolated from the LRU
  	 * list by either parallel reclaimers or compaction. If there are,
  	 * delay for some time until fewer pages are isolated
  	 */
  	while (unlikely(too_many_isolated(zone))) {
  		congestion_wait(BLK_RW_ASYNC, HZ/10);
  
  		if (fatal_signal_pending(current))
  			return 0;
  	}
  
  	/* Time to isolate some pages for migration */
  	spin_lock_irq(&zone->lru_lock);
  	for (; low_pfn < end_pfn; low_pfn++) {
  		struct page *page;
  		if (!pfn_valid_within(low_pfn))
  			continue;

  		nr_scanned++;

  
  		/* Get the page and skip if free */
  		page = pfn_to_page(low_pfn);
  		if (PageBuddy(page))
  			continue;

  		/*
  		 * For async migration, also only scan in MOVABLE blocks. Async
  		 * migration is optimistic to see if the minimum amount of work
  		 * satisfies the allocation
  		 */
  		pageblock_nr = low_pfn >> pageblock_order;
  		if (!cc->sync && last_pageblock_nr != pageblock_nr &&
  				get_pageblock_migratetype(page) != MIGRATE_MOVABLE) {
  			low_pfn += pageblock_nr_pages;
  			low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
  			last_pageblock_nr = pageblock_nr;
  			continue;
  		}

  		if (!PageLRU(page))
  			continue;
  
  		/*
  		 * PageLRU is set, and lru_lock excludes isolation,
  		 * splitting and collapsing (collapsing has already
  		 * happened if PageLRU is set).
  		 */
  		if (PageTransHuge(page)) {
  			low_pfn += (1 << compound_order(page)) - 1;
  			continue;
  		}

  		/* Try isolate the page */
  		if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
  			continue;

  		VM_BUG_ON(PageTransCompound(page));

  		/* Successfully isolated */
  		del_page_from_lru_list(zone, page, page_lru(page));
  		list_add(&page->lru, migratelist);

  		cc->nr_migratepages++;

  		nr_isolated++;

  
  		/* Avoid isolating too much */
  		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
  			break;
  	}
  
  	acct_isolated(zone, cc);
  
  	spin_unlock_irq(&zone->lru_lock);
  	cc->migrate_pfn = low_pfn;

  	trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);

  	return cc->nr_migratepages;
  }
  
  /*
   * This is a migrate-callback that "allocates" freepages by taking pages
   * from the isolated freelists in the block we are migrating to.
   */
  static struct page *compaction_alloc(struct page *migratepage,
  					unsigned long data,
  					int **result)
  {
  	struct compact_control *cc = (struct compact_control *)data;
  	struct page *freepage;
  
  	/* Isolate free pages if necessary */
  	if (list_empty(&cc->freepages)) {
  		isolate_freepages(cc->zone, cc);
  
  		if (list_empty(&cc->freepages))
  			return NULL;
  	}
  
  	freepage = list_entry(cc->freepages.next, struct page, lru);
  	list_del(&freepage->lru);
  	cc->nr_freepages--;
  
  	return freepage;
  }
  
  /*
   * We cannot control nr_migratepages and nr_freepages fully when migration is
   * running as migrate_pages() has no knowledge of compact_control. When
   * migration is complete, we count the number of pages on the lists by hand.
   */
  static void update_nr_listpages(struct compact_control *cc)
  {
  	int nr_migratepages = 0;
  	int nr_freepages = 0;
  	struct page *page;
  
  	list_for_each_entry(page, &cc->migratepages, lru)
  		nr_migratepages++;
  	list_for_each_entry(page, &cc->freepages, lru)
  		nr_freepages++;
  
  	cc->nr_migratepages = nr_migratepages;
  	cc->nr_freepages = nr_freepages;
  }
  
  static int compact_finished(struct zone *zone,

  			    struct compact_control *cc)

  {

  	unsigned int order;

  	unsigned long watermark;

  	if (fatal_signal_pending(current))
  		return COMPACT_PARTIAL;
  
  	/* Compaction run completes if the migrate and free scanner meet */
  	if (cc->free_pfn <= cc->migrate_pfn)
  		return COMPACT_COMPLETE;

  	/* Compaction run is not finished if the watermark is not met */

  	if (cc->compact_mode != COMPACT_MODE_KSWAPD)
  		watermark = low_wmark_pages(zone);
  	else
  		watermark = high_wmark_pages(zone);
  	watermark += (1 << cc->order);

  	if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
  		return COMPACT_CONTINUE;

  	/*
  	 * order == -1 is expected when compacting via
  	 * /proc/sys/vm/compact_memory
  	 */

  	if (cc->order == -1)
  		return COMPACT_CONTINUE;

  	/*
  	 * Generating only one page of the right order is not enough
  	 * for kswapd, we must continue until we're above the high
  	 * watermark as a pool for high order GFP_ATOMIC allocations
  	 * too.
  	 */
  	if (cc->compact_mode == COMPACT_MODE_KSWAPD)
  		return COMPACT_CONTINUE;

  	/* Direct compactor: Is a suitable page free? */
  	for (order = cc->order; order < MAX_ORDER; order++) {
  		/* Job done if page is free of the right migratetype */
  		if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
  			return COMPACT_PARTIAL;
  
  		/* Job done if allocation would set block type */
  		if (order >= pageblock_order && zone->free_area[order].nr_free)
  			return COMPACT_PARTIAL;
  	}

  	return COMPACT_CONTINUE;
  }

  /*
   * compaction_suitable: Is this suitable to run compaction on this zone now?
   * Returns
   *   COMPACT_SKIPPED  - If there are too few free pages for compaction
   *   COMPACT_PARTIAL  - If the allocation would succeed without compaction
   *   COMPACT_CONTINUE - If compaction should run now
   */
  unsigned long compaction_suitable(struct zone *zone, int order)
  {
  	int fragindex;
  	unsigned long watermark;
  
  	/*
  	 * Watermarks for order-0 must be met for compaction. Note the 2UL.
  	 * This is because during migration, copies of pages need to be
  	 * allocated and for a short time, the footprint is higher
  	 */
  	watermark = low_wmark_pages(zone) + (2UL << order);
  	if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
  		return COMPACT_SKIPPED;
  
  	/*

  	 * order == -1 is expected when compacting via
  	 * /proc/sys/vm/compact_memory
  	 */
  	if (order == -1)
  		return COMPACT_CONTINUE;
  
  	/*

  	 * fragmentation index determines if allocation failures are due to
  	 * low memory or external fragmentation
  	 *
  	 * index of -1 implies allocations might succeed dependingon watermarks
  	 * index towards 0 implies failure is due to lack of memory
  	 * index towards 1000 implies failure is due to fragmentation
  	 *
  	 * Only compact if a failure would be due to fragmentation.
  	 */
  	fragindex = fragmentation_index(zone, order);
  	if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
  		return COMPACT_SKIPPED;
  
  	if (fragindex == -1 && zone_watermark_ok(zone, order, watermark, 0, 0))
  		return COMPACT_PARTIAL;
  
  	return COMPACT_CONTINUE;
  }

  static int compact_zone(struct zone *zone, struct compact_control *cc)
  {
  	int ret;

  	ret = compaction_suitable(zone, cc->order);
  	switch (ret) {
  	case COMPACT_PARTIAL:
  	case COMPACT_SKIPPED:
  		/* Compaction is likely to fail */
  		return ret;
  	case COMPACT_CONTINUE:
  		/* Fall through to compaction */
  		;
  	}

  	/* Setup to move all movable pages to the end of the zone */
  	cc->migrate_pfn = zone->zone_start_pfn;
  	cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
  	cc->free_pfn &= ~(pageblock_nr_pages-1);
  
  	migrate_prep_local();
  
  	while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
  		unsigned long nr_migrate, nr_remaining;
  
  		if (!isolate_migratepages(zone, cc))
  			continue;
  
  		nr_migrate = cc->nr_migratepages;
  		migrate_pages(&cc->migratepages, compaction_alloc,

  				(unsigned long)cc, false,

  				cc->sync);

  		update_nr_listpages(cc);
  		nr_remaining = cc->nr_migratepages;
  
  		count_vm_event(COMPACTBLOCKS);
  		count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
  		if (nr_remaining)
  			count_vm_events(COMPACTPAGEFAILED, nr_remaining);

  		trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
  						nr_remaining);

  
  		/* Release LRU pages not migrated */
  		if (!list_empty(&cc->migratepages)) {
  			putback_lru_pages(&cc->migratepages);
  			cc->nr_migratepages = 0;
  		}
  
  	}
  
  	/* Release free pages and check accounting */
  	cc->nr_freepages -= release_freepages(&cc->freepages);
  	VM_BUG_ON(cc->nr_freepages != 0);
  
  	return ret;
  }

  unsigned long compact_zone_order(struct zone *zone,

  				 int order, gfp_t gfp_mask,
  				 bool sync,
  				 int compact_mode)

  {
  	struct compact_control cc = {
  		.nr_freepages = 0,
  		.nr_migratepages = 0,
  		.order = order,
  		.migratetype = allocflags_to_migratetype(gfp_mask),
  		.zone = zone,

  		.sync = sync,

  		.compact_mode = compact_mode,

  	};
  	INIT_LIST_HEAD(&cc.freepages);
  	INIT_LIST_HEAD(&cc.migratepages);
  
  	return compact_zone(zone, &cc);
  }

  int sysctl_extfrag_threshold = 500;

  /**
   * try_to_compact_pages - Direct compact to satisfy a high-order allocation
   * @zonelist: The zonelist used for the current allocation
   * @order: The order of the current allocation
   * @gfp_mask: The GFP mask of the current allocation
   * @nodemask: The allowed nodes to allocate from

   * @sync: Whether migration is synchronous or not

   *
   * This is the main entry point for direct page compaction.
   */
  unsigned long try_to_compact_pages(struct zonelist *zonelist,

  			int order, gfp_t gfp_mask, nodemask_t *nodemask,
  			bool sync)

  {
  	enum zone_type high_zoneidx = gfp_zone(gfp_mask);
  	int may_enter_fs = gfp_mask & __GFP_FS;
  	int may_perform_io = gfp_mask & __GFP_IO;

  	struct zoneref *z;
  	struct zone *zone;
  	int rc = COMPACT_SKIPPED;
  
  	/*
  	 * Check whether it is worth even starting compaction. The order check is
  	 * made because an assumption is made that the page allocator can satisfy
  	 * the "cheaper" orders without taking special steps
  	 */

  	if (!order || !may_enter_fs || !may_perform_io)

  		return rc;
  
  	count_vm_event(COMPACTSTALL);
  
  	/* Compact each zone in the list */
  	for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
  								nodemask) {

  		int status;

  		status = compact_zone_order(zone, order, gfp_mask, sync,
  					    COMPACT_MODE_DIRECT_RECLAIM);

  		rc = max(status, rc);

  		/* If a normal allocation would succeed, stop compacting */
  		if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))

  			break;
  	}
  
  	return rc;
  }

  /* Compact all zones within a node */
  static int compact_node(int nid)
  {
  	int zoneid;
  	pg_data_t *pgdat;
  	struct zone *zone;
  
  	if (nid < 0 || nid >= nr_node_ids || !node_online(nid))
  		return -EINVAL;
  	pgdat = NODE_DATA(nid);
  
  	/* Flush pending updates to the LRU lists */
  	lru_add_drain_all();
  
  	for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
  		struct compact_control cc = {
  			.nr_freepages = 0,
  			.nr_migratepages = 0,

  			.order = -1,

  			.compact_mode = COMPACT_MODE_DIRECT_RECLAIM,

  		};
  
  		zone = &pgdat->node_zones[zoneid];
  		if (!populated_zone(zone))
  			continue;
  
  		cc.zone = zone;
  		INIT_LIST_HEAD(&cc.freepages);
  		INIT_LIST_HEAD(&cc.migratepages);
  
  		compact_zone(zone, &cc);
  
  		VM_BUG_ON(!list_empty(&cc.freepages));
  		VM_BUG_ON(!list_empty(&cc.migratepages));
  	}
  
  	return 0;
  }
  
  /* Compact all nodes in the system */
  static int compact_nodes(void)
  {
  	int nid;
  
  	for_each_online_node(nid)
  		compact_node(nid);
  
  	return COMPACT_COMPLETE;
  }
  
  /* The written value is actually unused, all memory is compacted */
  int sysctl_compact_memory;
  
  /* This is the entry point for compacting all nodes via /proc/sys/vm */
  int sysctl_compaction_handler(struct ctl_table *table, int write,
  			void __user *buffer, size_t *length, loff_t *ppos)
  {
  	if (write)
  		return compact_nodes();
  
  	return 0;
  }

  int sysctl_extfrag_handler(struct ctl_table *table, int write,
  			void __user *buffer, size_t *length, loff_t *ppos)
  {
  	proc_dointvec_minmax(table, write, buffer, length, ppos);
  
  	return 0;
  }

  #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
  ssize_t sysfs_compact_node(struct sys_device *dev,
  			struct sysdev_attribute *attr,
  			const char *buf, size_t count)
  {
  	compact_node(dev->id);
  
  	return count;
  }
  static SYSDEV_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
  
  int compaction_register_node(struct node *node)
  {
  	return sysdev_create_file(&node->sysdev, &attr_compact);
  }
  
  void compaction_unregister_node(struct node *node)
  {
  	return sysdev_remove_file(&node->sysdev, &attr_compact);
  }
  #endif /* CONFIG_SYSFS && CONFIG_NUMA */