page_alloc.c

	while (nr_pageblocks--) {
		set_pageblock_migratetype(pageblock_page, migratetype);
		pageblock_page += pageblock_nr_pages;
	}
}

/* Remove an element from the buddy allocator from the fallback list */
static inline struct page *
__rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
{
	struct free_area * area;
	int current_order;
	struct page *page;
	int migratetype, i;

	/* Find the largest possible block of pages in the other list */
	for (current_order = MAX_ORDER-1; current_order >= order;
						--current_order) {
		for (i = 0;; i++) {
			migratetype = fallbacks[start_migratetype][i];

			/* MIGRATE_RESERVE handled later if necessary */
			if (migratetype == MIGRATE_RESERVE)
				break;

			area = &(zone->free_area[current_order]);
			if (list_empty(&area->free_list[migratetype]))
				continue;

			page = list_entry(area->free_list[migratetype].next,
					struct page, lru);
			area->nr_free--;

			/*
			 * If breaking a large block of pages, move all free
			 * pages to the preferred allocation list. If falling
			 * back for a reclaimable kernel allocation, be more
			 * aggressive about taking ownership of free pages
			 *
			 * On the other hand, never change migration
			 * type of MIGRATE_CMA pageblocks nor move CMA
			 * pages on different free lists. We don't
			 * want unmovable pages to be allocated from
			 * MIGRATE_CMA areas.
			 */
			if (!is_migrate_cma(migratetype) &&
			    (unlikely(current_order >= pageblock_order / 2) ||
			     start_migratetype == MIGRATE_RECLAIMABLE ||
			     page_group_by_mobility_disabled)) {
				int pages;
				pages = move_freepages_block(zone, page,
								start_migratetype);

				/* Claim the whole block if over half of it is free */
				if (pages >= (1 << (pageblock_order-1)) ||
						page_group_by_mobility_disabled)
					set_pageblock_migratetype(page,
								start_migratetype);

				migratetype = start_migratetype;
			}

			/* Remove the page from the freelists */
			list_del(&page->lru);
			rmv_page_order(page);

			/* Take ownership for orders >= pageblock_order */
			if (current_order >= pageblock_order &&
			    !is_migrate_cma(migratetype))
				change_pageblock_range(page, current_order,
							start_migratetype);

			expand(zone, page, order, current_order, area,
			       is_migrate_cma(migratetype)
			     ? migratetype : start_migratetype);

			trace_mm_page_alloc_extfrag(page, order, current_order,
				start_migratetype, migratetype);

			return page;
		}
	}

	return NULL;
}

/*
 * Do the hard work of removing an element from the buddy allocator.
 * Call me with the zone->lock already held.
 */
static struct page *__rmqueue(struct zone *zone, unsigned int order,
						int migratetype)
{
	struct page *page;

retry_reserve:
	page = __rmqueue_smallest(zone, order, migratetype);

	if (unlikely(!page) && migratetype != MIGRATE_RESERVE) {
		page = __rmqueue_fallback(zone, order, migratetype);

		/*
		 * Use MIGRATE_RESERVE rather than fail an allocation. goto
		 * is used because __rmqueue_smallest is an inline function
		 * and we want just one call site
		 */
		if (!page) {
			migratetype = MIGRATE_RESERVE;
			goto retry_reserve;
		}
	}

	trace_mm_page_alloc_zone_locked(page, order, migratetype);
	return page;
}

/*
 * Obtain a specified number of elements from the buddy allocator, all under
 * a single hold of the lock, for efficiency.  Add them to the supplied list.
 * Returns the number of new pages which were placed at *list.
 */
static int rmqueue_bulk(struct zone *zone, unsigned int order,
			unsigned long count, struct list_head *list,
			int migratetype, int cold)
{
	int mt = migratetype, i;

	spin_lock(&zone->lock);
	for (i = 0; i < count; ++i) {
		struct page *page = __rmqueue(zone, order, migratetype);
		if (unlikely(page == NULL))
			break;

		/*
		 * Split buddy pages returned by expand() are received here
		 * in physical page order. The page is added to the callers and
		 * list and the list head then moves forward. From the callers
		 * perspective, the linked list is ordered by page number in
		 * some conditions. This is useful for IO devices that can
		 * merge IO requests if the physical pages are ordered
		 * properly.
		 */
		if (likely(cold == 0))
			list_add(&page->lru, list);
		else
			list_add_tail(&page->lru, list);
		if (IS_ENABLED(CONFIG_CMA)) {
			mt = get_pageblock_migratetype(page);
			if (!is_migrate_cma(mt) && !is_migrate_isolate(mt))
				mt = migratetype;
		}
		set_freepage_migratetype(page, mt);
		list = &page->lru;
		if (is_migrate_cma(mt))
			__mod_zone_page_state(zone, NR_FREE_CMA_PAGES,
					      -(1 << order));
	}
	__mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order));
	spin_unlock(&zone->lock);
	return i;
}

#ifdef CONFIG_NUMA
/*
 * Called from the vmstat counter updater to drain pagesets of this
 * currently executing processor on remote nodes after they have
 * expired.
 *
 * Note that this function must be called with the thread pinned to
 * a single processor.
 */
void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp)
{
	unsigned long flags;
	int to_drain;
	unsigned long batch;

	local_irq_save(flags);
	batch = ACCESS_ONCE(pcp->batch);
	if (pcp->count >= batch)
		to_drain = batch;
	else
		to_drain = pcp->count;
	if (to_drain > 0) {
		free_pcppages_bulk(zone, to_drain, pcp);
		pcp->count -= to_drain;
	}
	local_irq_restore(flags);
}
#endif

/*
 * Drain pages of the indicated processor.
 *
 * The processor must either be the current processor and the
 * thread pinned to the current processor or a processor that
 * is not online.
 */
static void drain_pages(unsigned int cpu)
{
	unsigned long flags;
	struct zone *zone;

	for_each_populated_zone(zone) {
		struct per_cpu_pageset *pset;
		struct per_cpu_pages *pcp;

		local_irq_save(flags);
		pset = per_cpu_ptr(zone->pageset, cpu);

		pcp = &pset->pcp;
		if (pcp->count) {
			free_pcppages_bulk(zone, pcp->count, pcp);
			pcp->count = 0;
		}
		local_irq_restore(flags);
	}
}

/*
 * Spill all of this CPU's per-cpu pages back into the buddy allocator.
 */
void drain_local_pages(void *arg)
{
	drain_pages(smp_processor_id());
}

/*
 * Spill all the per-cpu pages from all CPUs back into the buddy allocator.
 *
 * Note that this code is protected against sending an IPI to an offline
 * CPU but does not guarantee sending an IPI to newly hotplugged CPUs:
 * on_each_cpu_mask() blocks hotplug and won't talk to offlined CPUs but
 * nothing keeps CPUs from showing up after we populated the cpumask and
 * before the call to on_each_cpu_mask().
 */
void drain_all_pages(void)
{
	int cpu;
	struct per_cpu_pageset *pcp;
	struct zone *zone;

	/*
	 * Allocate in the BSS so we wont require allocation in
	 * direct reclaim path for CONFIG_CPUMASK_OFFSTACK=y
	 */
	static cpumask_t cpus_with_pcps;

	/*
	 * We don't care about racing with CPU hotplug event
	 * as offline notification will cause the notified
	 * cpu to drain that CPU pcps and on_each_cpu_mask
	 * disables preemption as part of its processing
	 */
	for_each_online_cpu(cpu) {
		bool has_pcps = false;
		for_each_populated_zone(zone) {
			pcp = per_cpu_ptr(zone->pageset, cpu);
			if (pcp->pcp.count) {
				has_pcps = true;
				break;
			}
		}
		if (has_pcps)
			cpumask_set_cpu(cpu, &cpus_with_pcps);
		else
			cpumask_clear_cpu(cpu, &cpus_with_pcps);
	}
	on_each_cpu_mask(&cpus_with_pcps, drain_local_pages, NULL, 1);
}

#ifdef CONFIG_HIBERNATION

void mark_free_pages(struct zone *zone)
{
	unsigned long pfn, max_zone_pfn;
	unsigned long flags;
	int order, t;
	struct list_head *curr;

	if (!zone->spanned_pages)
		return;

	spin_lock_irqsave(&zone->lock, flags);

	max_zone_pfn = zone_end_pfn(zone);
	for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++)
		if (pfn_valid(pfn)) {
			struct page *page = pfn_to_page(pfn);

			if (!swsusp_page_is_forbidden(page))
				swsusp_unset_page_free(page);
		}

	for_each_migratetype_order(order, t) {
		list_for_each(curr, &zone->free_area[order].free_list[t]) {
			unsigned long i;

			pfn = page_to_pfn(list_entry(curr, struct page, lru));
			for (i = 0; i < (1UL << order); i++)
				swsusp_set_page_free(pfn_to_page(pfn + i));
		}
	}
	spin_unlock_irqrestore(&zone->lock, flags);
}
#endif /* CONFIG_PM */

/*
 * Free a 0-order page
 * cold == 1 ? free a cold page : free a hot page
 */
void free_hot_cold_page(struct page *page, int cold)
{
	struct zone *zone = page_zone(page);
	struct per_cpu_pages *pcp;
	unsigned long flags;
	int migratetype;

	if (!free_pages_prepare(page, 0))
		return;

	migratetype = get_pageblock_migratetype(page);
	set_freepage_migratetype(page, migratetype);
	local_irq_save(flags);
	__count_vm_event(PGFREE);

	/*
	 * We only track unmovable, reclaimable and movable on pcp lists.
	 * Free ISOLATE pages back to the allocator because they are being
	 * offlined but treat RESERVE as movable pages so we can get those
	 * areas back if necessary. Otherwise, we may have to free
	 * excessively into the page allocator
	 */
	if (migratetype >= MIGRATE_PCPTYPES) {
		if (unlikely(is_migrate_isolate(migratetype))) {
			free_one_page(zone, page, 0, migratetype);
			goto out;
		}
		migratetype = MIGRATE_MOVABLE;
	}

	pcp = &this_cpu_ptr(zone->pageset)->pcp;
	if (cold)
		list_add_tail(&page->lru, &pcp->lists[migratetype]);
	else
		list_add(&page->lru, &pcp->lists[migratetype]);
	pcp->count++;
	if (pcp->count >= pcp->high) {
		unsigned long batch = ACCESS_ONCE(pcp->batch);
		free_pcppages_bulk(zone, batch, pcp);
		pcp->count -= batch;
	}

out:
	local_irq_restore(flags);
}

/*
 * Free a list of 0-order pages
 */
void free_hot_cold_page_list(struct list_head *list, int cold)
{
	struct page *page, *next;

	list_for_each_entry_safe(page, next, list, lru) {
		trace_mm_page_free_batched(page, cold);
		free_hot_cold_page(page, cold);
	}
}

/*
 * split_page takes a non-compound higher-order page, and splits it into
 * n (1<<order) sub-pages: page[0..n]
 * Each sub-page must be freed individually.
 *
 * Note: this is probably too low level an operation for use in drivers.
 * Please consult with lkml before using this in your driver.
 */
void split_page(struct page *page, unsigned int order)
{
	int i;

	VM_BUG_ON(PageCompound(page));
	VM_BUG_ON(!page_count(page));

#ifdef CONFIG_KMEMCHECK
	/*
	 * Split shadow pages too, because free(page[0]) would
	 * otherwise free the whole shadow.
	 */
	if (kmemcheck_page_is_tracked(page))
		split_page(virt_to_page(page[0].shadow), order);
#endif

	for (i = 1; i < (1 << order); i++)
		set_page_refcounted(page + i);
}
EXPORT_SYMBOL_GPL(split_page);

static int __isolate_free_page(struct page *page, unsigned int order)
{
	unsigned long watermark;
	struct zone *zone;
	int mt;

	BUG_ON(!PageBuddy(page));

	zone = page_zone(page);
	mt = get_pageblock_migratetype(page);

	if (!is_migrate_isolate(mt)) {
		/* Obey watermarks as if the page was being allocated */
		watermark = low_wmark_pages(zone) + (1 << order);
		if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
			return 0;

		__mod_zone_freepage_state(zone, -(1UL << order), mt);
	}

	/* Remove page from free list */
	list_del(&page->lru);
	zone->free_area[order].nr_free--;
	rmv_page_order(page);

	/* Set the pageblock if the isolated page is at least a pageblock */
	if (order >= pageblock_order - 1) {
		struct page *endpage = page + (1 << order) - 1;
		for (; page < endpage; page += pageblock_nr_pages) {
			int mt = get_pageblock_migratetype(page);
			if (!is_migrate_isolate(mt) && !is_migrate_cma(mt))
				set_pageblock_migratetype(page,
							  MIGRATE_MOVABLE);
		}
	}

	return 1UL << order;
}

/*
 * Similar to split_page except the page is already free. As this is only
 * being used for migration, the migratetype of the block also changes.
 * As this is called with interrupts disabled, the caller is responsible
 * for calling arch_alloc_page() and kernel_map_page() after interrupts
 * are enabled.
 *
 * Note: this is probably too low level an operation for use in drivers.
 * Please consult with lkml before using this in your driver.
 */
int split_free_page(struct page *page)
{
	unsigned int order;
	int nr_pages;

	order = page_order(page);

	nr_pages = __isolate_free_page(page, order);
	if (!nr_pages)
		return 0;

	/* Split into individual pages */
	set_page_refcounted(page);
	split_page(page, order);
	return nr_pages;
}

/*
 * Really, prep_compound_page() should be called from __rmqueue_bulk().  But
 * we cheat by calling it from here, in the order > 0 path.  Saves a branch
 * or two.
 */
static inline
struct page *buffered_rmqueue(struct zone *preferred_zone,
			struct zone *zone, int order, gfp_t gfp_flags,
			int migratetype)
{
	unsigned long flags;
	struct page *page;
	int cold = !!(gfp_flags & __GFP_COLD);

again:
	if (likely(order == 0)) {
		struct per_cpu_pages *pcp;
		struct list_head *list;

		local_irq_save(flags);
		pcp = &this_cpu_ptr(zone->pageset)->pcp;
		list = &pcp->lists[migratetype];
		if (list_empty(list)) {
			pcp->count += rmqueue_bulk(zone, 0,
					pcp->batch, list,
					migratetype, cold);
			if (unlikely(list_empty(list)))
				goto failed;
		}

		if (cold)
			page = list_entry(list->prev, struct page, lru);
		else
			page = list_entry(list->next, struct page, lru);

		list_del(&page->lru);
		pcp->count--;
	} else {
		if (unlikely(gfp_flags & __GFP_NOFAIL)) {
			/*
			 * __GFP_NOFAIL is not to be used in new code.
			 *
			 * All __GFP_NOFAIL callers should be fixed so that they
			 * properly detect and handle allocation failures.
			 *
			 * We most definitely don't want callers attempting to
			 * allocate greater than order-1 page units with
			 * __GFP_NOFAIL.
			 */
			WARN_ON_ONCE(order > 1);
		}
		spin_lock_irqsave(&zone->lock, flags);
		page = __rmqueue(zone, order, migratetype);
		spin_unlock(&zone->lock);
		if (!page)
			goto failed;
		__mod_zone_freepage_state(zone, -(1 << order),
					  get_pageblock_migratetype(page));
	}

	__count_zone_vm_events(PGALLOC, zone, 1 << order);
	zone_statistics(preferred_zone, zone, gfp_flags);
	local_irq_restore(flags);

	VM_BUG_ON(bad_range(zone, page));
	if (prep_new_page(page, order, gfp_flags))
		goto again;
	return page;

failed:
	local_irq_restore(flags);
	return NULL;
}

#ifdef CONFIG_FAIL_PAGE_ALLOC

static struct {
	struct fault_attr attr;

	u32 ignore_gfp_highmem;
	u32 ignore_gfp_wait;
	u32 min_order;
} fail_page_alloc = {
	.attr = FAULT_ATTR_INITIALIZER,
	.ignore_gfp_wait = 1,
	.ignore_gfp_highmem = 1,
	.min_order = 1,
};

static int __init setup_fail_page_alloc(char *str)
{
	return setup_fault_attr(&fail_page_alloc.attr, str);
}
__setup("fail_page_alloc=", setup_fail_page_alloc);

static bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
{
	if (order < fail_page_alloc.min_order)
		return false;
	if (gfp_mask & __GFP_NOFAIL)
		return false;
	if (fail_page_alloc.ignore_gfp_highmem && (gfp_mask & __GFP_HIGHMEM))
		return false;
	if (fail_page_alloc.ignore_gfp_wait && (gfp_mask & __GFP_WAIT))
		return false;

	return should_fail(&fail_page_alloc.attr, 1 << order);
}

#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS

static int __init fail_page_alloc_debugfs(void)
{
	umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
	struct dentry *dir;

	dir = fault_create_debugfs_attr("fail_page_alloc", NULL,
					&fail_page_alloc.attr);
	if (IS_ERR(dir))
		return PTR_ERR(dir);

	if (!debugfs_create_bool("ignore-gfp-wait", mode, dir,
				&fail_page_alloc.ignore_gfp_wait))
		goto fail;
	if (!debugfs_create_bool("ignore-gfp-highmem", mode, dir,
				&fail_page_alloc.ignore_gfp_highmem))
		goto fail;
	if (!debugfs_create_u32("min-order", mode, dir,
				&fail_page_alloc.min_order))
		goto fail;

	return 0;
fail:
	debugfs_remove_recursive(dir);

	return -ENOMEM;
}

late_initcall(fail_page_alloc_debugfs);

#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */

#else /* CONFIG_FAIL_PAGE_ALLOC */

static inline bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
{
	return false;
}

#endif /* CONFIG_FAIL_PAGE_ALLOC */

/*
 * Return true if free pages are above 'mark'. This takes into account the order
 * of the allocation.
 */
static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark,
		      int classzone_idx, int alloc_flags, long free_pages)
{
	/* free_pages my go negative - that's OK */
	long min = mark;
	long lowmem_reserve = z->lowmem_reserve[classzone_idx];
	int o;
	long free_cma = 0;

	free_pages -= (1 << order) - 1;
	if (alloc_flags & ALLOC_HIGH)
		min -= min / 2;
	if (alloc_flags & ALLOC_HARDER)
		min -= min / 4;
#ifdef CONFIG_CMA
	/* If allocation can't use CMA areas don't use free CMA pages */
	if (!(alloc_flags & ALLOC_CMA))
		free_cma = zone_page_state(z, NR_FREE_CMA_PAGES);
#endif

	if (free_pages - free_cma <= min + lowmem_reserve)
		return false;
	for (o = 0; o < order; o++) {
		/* At the next order, this order's pages become unavailable */
		free_pages -= z->free_area[o].nr_free << o;

		/* Require fewer higher order pages to be free */
		min >>= 1;

		if (free_pages <= min)
			return false;
	}
	return true;
}

bool zone_watermark_ok(struct zone *z, int order, unsigned long mark,
		      int classzone_idx, int alloc_flags)
{
	return __zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags,
					zone_page_state(z, NR_FREE_PAGES));
}

bool zone_watermark_ok_safe(struct zone *z, int order, unsigned long mark,
		      int classzone_idx, int alloc_flags)
{
	long free_pages = zone_page_state(z, NR_FREE_PAGES);

	if (z->percpu_drift_mark && free_pages < z->percpu_drift_mark)
		free_pages = zone_page_state_snapshot(z, NR_FREE_PAGES);

	return __zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags,
								free_pages);
}

#ifdef CONFIG_NUMA
/*
 * zlc_setup - Setup for "zonelist cache".  Uses cached zone data to
 * skip over zones that are not allowed by the cpuset, or that have
 * been recently (in last second) found to be nearly full.  See further
 * comments in mmzone.h.  Reduces cache footprint of zonelist scans
 * that have to skip over a lot of full or unallowed zones.
 *
 * If the zonelist cache is present in the passed in zonelist, then
 * returns a pointer to the allowed node mask (either the current
 * tasks mems_allowed, or node_states[N_MEMORY].)
 *
 * If the zonelist cache is not available for this zonelist, does
 * nothing and returns NULL.
 *
 * If the fullzones BITMAP in the zonelist cache is stale (more than
 * a second since last zap'd) then we zap it out (clear its bits.)
 *
 * We hold off even calling zlc_setup, until after we've checked the
 * first zone in the zonelist, on the theory that most allocations will
 * be satisfied from that first zone, so best to examine that zone as
 * quickly as we can.
 */
static nodemask_t *zlc_setup(struct zonelist *zonelist, int alloc_flags)
{
	struct zonelist_cache *zlc;	/* cached zonelist speedup info */
	nodemask_t *allowednodes;	/* zonelist_cache approximation */

	zlc = zonelist->zlcache_ptr;
	if (!zlc)
		return NULL;

	if (time_after(jiffies, zlc->last_full_zap + HZ)) {
		bitmap_zero(zlc->fullzones, MAX_ZONES_PER_ZONELIST);
		zlc->last_full_zap = jiffies;
	}

	allowednodes = !in_interrupt() && (alloc_flags & ALLOC_CPUSET) ?
					&cpuset_current_mems_allowed :
					&node_states[N_MEMORY];
	return allowednodes;
}

/*
 * Given 'z' scanning a zonelist, run a couple of quick checks to see
 * if it is worth looking at further for free memory:
 *  1) Check that the zone isn't thought to be full (doesn't have its
 *     bit set in the zonelist_cache fullzones BITMAP).
 *  2) Check that the zones node (obtained from the zonelist_cache
 *     z_to_n[] mapping) is allowed in the passed in allowednodes mask.
 * Return true (non-zero) if zone is worth looking at further, or
 * else return false (zero) if it is not.
 *
 * This check -ignores- the distinction between various watermarks,
 * such as GFP_HIGH, GFP_ATOMIC, PF_MEMALLOC, ...  If a zone is
 * found to be full for any variation of these watermarks, it will
 * be considered full for up to one second by all requests, unless
 * we are so low on memory on all allowed nodes that we are forced
 * into the second scan of the zonelist.
 *
 * In the second scan we ignore this zonelist cache and exactly
 * apply the watermarks to all zones, even it is slower to do so.
 * We are low on memory in the second scan, and should leave no stone
 * unturned looking for a free page.
 */
static int zlc_zone_worth_trying(struct zonelist *zonelist, struct zoneref *z,
						nodemask_t *allowednodes)
{
	struct zonelist_cache *zlc;	/* cached zonelist speedup info */
	int i;				/* index of *z in zonelist zones */
	int n;				/* node that zone *z is on */

	zlc = zonelist->zlcache_ptr;
	if (!zlc)
		return 1;

	i = z - zonelist->_zonerefs;
	n = zlc->z_to_n[i];

	/* This zone is worth trying if it is allowed but not full */
	return node_isset(n, *allowednodes) && !test_bit(i, zlc->fullzones);
}

/*
 * Given 'z' scanning a zonelist, set the corresponding bit in
 * zlc->fullzones, so that subsequent attempts to allocate a page
 * from that zone don't waste time re-examining it.
 */
static void zlc_mark_zone_full(struct zonelist *zonelist, struct zoneref *z)
{
	struct zonelist_cache *zlc;	/* cached zonelist speedup info */
	int i;				/* index of *z in zonelist zones */

	zlc = zonelist->zlcache_ptr;
	if (!zlc)
		return;

	i = z - zonelist->_zonerefs;

	set_bit(i, zlc->fullzones);
}

/*
 * clear all zones full, called after direct reclaim makes progress so that
 * a zone that was recently full is not skipped over for up to a second
 */
static void zlc_clear_zones_full(struct zonelist *zonelist)
{
	struct zonelist_cache *zlc;	/* cached zonelist speedup info */

	zlc = zonelist->zlcache_ptr;
	if (!zlc)
		return;

	bitmap_zero(zlc->fullzones, MAX_ZONES_PER_ZONELIST);
}

static bool zone_allows_reclaim(struct zone *local_zone, struct zone *zone)
{
	return node_isset(local_zone->node, zone->zone_pgdat->reclaim_nodes);
}

static void __paginginit init_zone_allows_reclaim(int nid)
{
	int i;

	for_each_online_node(i)
		if (node_distance(nid, i) <= RECLAIM_DISTANCE)
			node_set(i, NODE_DATA(nid)->reclaim_nodes);
		else
			zone_reclaim_mode = 1;
}

#else	/* CONFIG_NUMA */

static nodemask_t *zlc_setup(struct zonelist *zonelist, int alloc_flags)
{
	return NULL;
}

static int zlc_zone_worth_trying(struct zonelist *zonelist, struct zoneref *z,
				nodemask_t *allowednodes)
{
	return 1;
}

static void zlc_mark_zone_full(struct zonelist *zonelist, struct zoneref *z)
{
}

static void zlc_clear_zones_full(struct zonelist *zonelist)
{
}

static bool zone_allows_reclaim(struct zone *local_zone, struct zone *zone)
{
	return true;
}

static inline void init_zone_allows_reclaim(int nid)
{
}
#endif	/* CONFIG_NUMA */

/*
 * get_page_from_freelist goes through the zonelist trying to allocate
 * a page.
 */
static struct page *
get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order,
		struct zonelist *zonelist, int high_zoneidx, int alloc_flags,
		struct zone *preferred_zone, int migratetype)
{
	struct zoneref *z;
	struct page *page = NULL;
	int classzone_idx;
	struct zone *zone;
	nodemask_t *allowednodes = NULL;/* zonelist_cache approximation */
	int zlc_active = 0;		/* set if using zonelist_cache */
	int did_zlc_setup = 0;		/* just call zlc_setup() one time */

	classzone_idx = zone_idx(preferred_zone);
zonelist_scan:
	/*
	 * Scan zonelist, looking for a zone with enough free.
	 * See also cpuset_zone_allowed() comment in kernel/cpuset.c.
	 */
	for_each_zone_zonelist_nodemask(zone, z, zonelist,
						high_zoneidx, nodemask) {
		if (IS_ENABLED(CONFIG_NUMA) && zlc_active &&
			!zlc_zone_worth_trying(zonelist, z, allowednodes))
				continue;
		if ((alloc_flags & ALLOC_CPUSET) &&
			!cpuset_zone_allowed_softwall(zone, gfp_mask))
				continue;
		/*
		 * When allocating a page cache page for writing, we
		 * want to get it from a zone that is within its dirty
		 * limit, such that no single zone holds more than its
		 * proportional share of globally allowed dirty pages.
		 * The dirty limits take into account the zone's
		 * lowmem reserves and high watermark so that kswapd
		 * should be able to balance it without having to
		 * write pages from its LRU list.
		 *
		 * This may look like it could increase pressure on
		 * lower zones by failing allocations in higher zones
		 * before they are full.  But the pages that do spill
		 * over are limited as the lower zones are protected
		 * by this very same mechanism.  It should not become
		 * a practical burden to them.
		 *
		 * XXX: For now, allow allocations to potentially
		 * exceed the per-zone dirty limit in the slowpath
		 * (ALLOC_WMARK_LOW unset) before going into reclaim,
		 * which is important when on a NUMA setup the allowed
		 * zones are together not big enough to reach the
		 * global limit.  The proper fix for these situations
		 * will require awareness of zones in the
		 * dirty-throttling and the flusher threads.
		 */
		if ((alloc_flags & ALLOC_WMARK_LOW) &&
		    (gfp_mask & __GFP_WRITE) && !zone_dirty_ok(zone))
			goto this_zone_full;

		BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK);
		if (!(alloc_flags & ALLOC_NO_WATERMARKS)) {
			unsigned long mark;
			int ret;

			mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
			if (zone_watermark_ok(zone, order, mark,
				    classzone_idx, alloc_flags))
				goto try_this_zone;

			if (IS_ENABLED(CONFIG_NUMA) &&
					!did_zlc_setup && nr_online_nodes > 1) {
				/*
				 * we do zlc_setup if there are multiple nodes
				 * and before considering the first zone allowed
				 * by the cpuset.
				 */
				allowednodes = zlc_setup(zonelist, alloc_flags);
				zlc_active = 1;
				did_zlc_setup = 1;
			}

			if (zone_reclaim_mode == 0 ||
			    !zone_allows_reclaim(preferred_zone, zone))
				goto this_zone_full;

			/*
			 * As we may have just activated ZLC, check if the first
			 * eligible zone has failed zone_reclaim recently.
			 */
			if (IS_ENABLED(CONFIG_NUMA) && zlc_active &&
				!zlc_zone_worth_trying(zonelist, z, allowednodes))
				continue;

			ret = zone_reclaim(zone, gfp_mask, order);
			switch (ret) {
			case ZONE_RECLAIM_NOSCAN:
				/* did not scan */
				continue;
			case ZONE_RECLAIM_FULL:
				/* scanned but unreclaimable */
				continue;
			default:
				/* did we reclaim enough */
				if (zone_watermark_ok(zone, order, mark,
						classzone_idx, alloc_flags))
					goto try_this_zone;

				/*
				 * Failed to reclaim enough to meet watermark.
				 * Only mark the zone full if checking the min
				 * watermark or if we failed to reclaim just
				 * 1<<order pages or else the page allocator
				 * fastpath will prematurely mark zones full
				 * when the watermark is between the low and
				 * min watermarks.
				 */
				if (((alloc_flags & ALLOC_WMARK_MASK) == ALLOC_WMARK_MIN) ||
				    ret == ZONE_RECLAIM_SOME)
					goto this_zone_full;

				continue;
			}
		}

try_this_zone:
		page = buffered_rmqueue(preferred_zone, zone, order,
						gfp_mask, migratetype);
		if (page)
			break;
this_zone_full:
		if (IS_ENABLED(CONFIG_NUMA))
			zlc_mark_zone_full(zonelist, z);
	}

	if (unlikely(IS_ENABLED(CONFIG_NUMA) && page == NULL && zlc_active)) {
		/* Disable zlc cache for second zonelist scan */
		zlc_active = 0;
		goto zonelist_scan;
	}

	if (page)
		/*
		 * page->pfmemalloc is set when ALLOC_NO_WATERMARKS was
		 * necessary to allocate the page. The expectation is
		 * that the caller is taking steps that will free more
		 * memory. The caller should avoid the page being used
		 * for !PFMEMALLOC purposes.
		 */
		page->pfmemalloc = !!(alloc_flags & ALLOC_NO_WATERMARKS);

	return page;
}

/*
 * Large machines with many possible nodes should not always dump per-node
 * meminfo in irq context.
 */
static inline bool should_suppress_show_mem(void)
{