mm/page_alloc.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/mm/page_alloc.c
 *
 *  Manages the free list, the system allocates free pages here.
 *  Note that kmalloc() lives in slab.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *  Swap reorganised 29.12.95, Stephen Tweedie
 *  Support of BIGMEM added by Gerhard Wichert, Siemens AG, July 1999
 *  Reshaped it to be a zoned allocator, Ingo Molnar, Red Hat, 1999
 *  Discontiguous memory support, Kanoj Sarcar, SGI, Nov 1999
 *  Zone balancing, Kanoj Sarcar, SGI, Jan 2000
 *  Per cpu hot/cold page lists, bulk allocation, Martin J. Bligh, Sept 2002
 *          (lots of bits borrowed from Ingo Molnar & Andrew Morton)
 */

#include <linux/stddef.h>
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/interrupt.h>
#include <linux/jiffies.h>
#include <linux/compiler.h>
#include <linux/kernel.h>
#include <linux/kasan.h>
#include <linux/kmsan.h>
#include <linux/module.h>
#include <linux/suspend.h>
#include <linux/ratelimit.h>
#include <linux/oom.h>
#include <linux/topology.h>
#include <linux/sysctl.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/pagevec.h>
#include <linux/memory_hotplug.h>
#include <linux/nodemask.h>
#include <linux/vmstat.h>
#include <linux/fault-inject.h>
#include <linux/compaction.h>
#include <trace/events/kmem.h>
#include <trace/events/oom.h>
#include <linux/prefetch.h>
#include <linux/mm_inline.h>
#include <linux/mmu_notifier.h>
#include <linux/migrate.h>
#include <linux/sched/mm.h>
#include <linux/page_owner.h>
#include <linux/page_table_check.h>
#include <linux/memcontrol.h>
#include <linux/ftrace.h>
#include <linux/lockdep.h>
#include <linux/psi.h>
#include <linux/khugepaged.h>
#include <linux/delayacct.h>
#include <linux/cacheinfo.h>
#include <linux/pgalloc_tag.h>
#include <asm/div64.h>
#include "internal.h"
#include "shuffle.h"
#include "page_reporting.h"

/* Free Page Internal flags: for internal, non-pcp variants of free_pages(). */
typedef int __bitwise fpi_t;

/* No special request */
#define FPI_NONE		((__force fpi_t)0)

/*
 * Skip free page reporting notification for the (possibly merged) page.
 * This does not hinder free page reporting from grabbing the page,
 * reporting it and marking it "reported" -  it only skips notifying
 * the free page reporting infrastructure about a newly freed page. For
 * example, used when temporarily pulling a page from a freelist and
 * putting it back unmodified.
 */
#define FPI_SKIP_REPORT_NOTIFY	((__force fpi_t)BIT(0))

/*
 * Place the (possibly merged) page to the tail of the freelist. Will ignore
 * page shuffling (relevant code - e.g., memory onlining - is expected to
 * shuffle the whole zone).
 *
 * Note: No code should rely on this flag for correctness - it's purely
 *       to allow for optimizations when handing back either fresh pages
 *       (memory onlining) or untouched pages (page isolation, free page
 *       reporting).
 */
#define FPI_TO_TAIL		((__force fpi_t)BIT(1))

/* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
static DEFINE_MUTEX(pcp_batch_high_lock);
#define MIN_PERCPU_PAGELIST_HIGH_FRACTION (8)

#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
/*
 * On SMP, spin_trylock is sufficient protection.
 * On PREEMPT_RT, spin_trylock is equivalent on both SMP and UP.
 */
#define pcp_trylock_prepare(flags)	do { } while (0)
#define pcp_trylock_finish(flag)	do { } while (0)
#else

/* UP spin_trylock always succeeds so disable IRQs to prevent re-entrancy. */
#define pcp_trylock_prepare(flags)	local_irq_save(flags)
#define pcp_trylock_finish(flags)	local_irq_restore(flags)
#endif

/*
 * Locking a pcp requires a PCP lookup followed by a spinlock. To avoid
 * a migration causing the wrong PCP to be locked and remote memory being
 * potentially allocated, pin the task to the CPU for the lookup+lock.
 * preempt_disable is used on !RT because it is faster than migrate_disable.
 * migrate_disable is used on RT because otherwise RT spinlock usage is
 * interfered with and a high priority task cannot preempt the allocator.
 */
#ifndef CONFIG_PREEMPT_RT
#define pcpu_task_pin()		preempt_disable()
#define pcpu_task_unpin()	preempt_enable()
#else
#define pcpu_task_pin()		migrate_disable()
#define pcpu_task_unpin()	migrate_enable()
#endif

/*
 * Generic helper to lookup and a per-cpu variable with an embedded spinlock.
 * Return value should be used with equivalent unlock helper.
 */
#define pcpu_spin_lock(type, member, ptr)				\
({									\
	type *_ret;							\
	pcpu_task_pin();						\
	_ret = this_cpu_ptr(ptr);					\
	spin_lock(&_ret->member);					\
	_ret;								\
})

#define pcpu_spin_trylock(type, member, ptr)				\
({									\
	type *_ret;							\
	pcpu_task_pin();						\
	_ret = this_cpu_ptr(ptr);					\
	if (!spin_trylock(&_ret->member)) {				\
		pcpu_task_unpin();					\
		_ret = NULL;						\
	}								\
	_ret;								\
})

#define pcpu_spin_unlock(member, ptr)					\
({									\
	spin_unlock(&ptr->member);					\
	pcpu_task_unpin();						\
})

/* struct per_cpu_pages specific helpers. */
#define pcp_spin_lock(ptr)						\
	pcpu_spin_lock(struct per_cpu_pages, lock, ptr)

#define pcp_spin_trylock(ptr)						\
	pcpu_spin_trylock(struct per_cpu_pages, lock, ptr)

#define pcp_spin_unlock(ptr)						\
	pcpu_spin_unlock(lock, ptr)

#ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
DEFINE_PER_CPU(int, numa_node);
EXPORT_PER_CPU_SYMBOL(numa_node);
#endif

DEFINE_STATIC_KEY_TRUE(vm_numa_stat_key);

#ifdef CONFIG_HAVE_MEMORYLESS_NODES
/*
 * N.B., Do NOT reference the '_numa_mem_' per cpu variable directly.
 * It will not be defined when CONFIG_HAVE_MEMORYLESS_NODES is not defined.
 * Use the accessor functions set_numa_mem(), numa_mem_id() and cpu_to_mem()
 * defined in <linux/topology.h>.
 */
DEFINE_PER_CPU(int, _numa_mem_);		/* Kernel "local memory" node */
EXPORT_PER_CPU_SYMBOL(_numa_mem_);
#endif

static DEFINE_MUTEX(pcpu_drain_mutex);

#ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY
volatile unsigned long latent_entropy __latent_entropy;
EXPORT_SYMBOL(latent_entropy);
#endif

/*
 * Array of node states.
 */
nodemask_t node_states[NR_NODE_STATES] __read_mostly = {
	[N_POSSIBLE] = NODE_MASK_ALL,
	[N_ONLINE] = { { [0] = 1UL } },
#ifndef CONFIG_NUMA
	[N_NORMAL_MEMORY] = { { [0] = 1UL } },
#ifdef CONFIG_HIGHMEM
	[N_HIGH_MEMORY] = { { [0] = 1UL } },
#endif
	[N_MEMORY] = { { [0] = 1UL } },
	[N_CPU] = { { [0] = 1UL } },
#endif	/* NUMA */
};
EXPORT_SYMBOL(node_states);

gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;

#ifdef CONFIG_HUGETLB_PAGE_SIZE_VARIABLE
unsigned int pageblock_order __read_mostly;
#endif

static void __free_pages_ok(struct page *page, unsigned int order,
			    fpi_t fpi_flags);

/*
 * results with 256, 32 in the lowmem_reserve sysctl:
 *	1G machine -> (16M dma, 800M-16M normal, 1G-800M high)
 *	1G machine -> (16M dma, 784M normal, 224M high)
 *	NORMAL allocation will leave 784M/256 of ram reserved in the ZONE_DMA
 *	HIGHMEM allocation will leave 224M/32 of ram reserved in ZONE_NORMAL
 *	HIGHMEM allocation will leave (224M+784M)/256 of ram reserved in ZONE_DMA
 *
 * TBD: should special case ZONE_DMA32 machines here - in those we normally
 * don't need any ZONE_NORMAL reservation
 */
static int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES] = {
#ifdef CONFIG_ZONE_DMA
	[ZONE_DMA] = 256,
#endif
#ifdef CONFIG_ZONE_DMA32
	[ZONE_DMA32] = 256,
#endif
	[ZONE_NORMAL] = 32,
#ifdef CONFIG_HIGHMEM
	[ZONE_HIGHMEM] = 0,
#endif
	[ZONE_MOVABLE] = 0,
};

char * const zone_names[MAX_NR_ZONES] = {
#ifdef CONFIG_ZONE_DMA
	 "DMA",
#endif
#ifdef CONFIG_ZONE_DMA32
	 "DMA32",
#endif
	 "Normal",
#ifdef CONFIG_HIGHMEM
	 "HighMem",
#endif
	 "Movable",
#ifdef CONFIG_ZONE_DEVICE
	 "Device",
#endif
};

const char * const migratetype_names[MIGRATE_TYPES] = {
	"Unmovable",
	"Movable",
	"Reclaimable",
	"HighAtomic",
#ifdef CONFIG_CMA
	"CMA",
#endif
#ifdef CONFIG_MEMORY_ISOLATION
	"Isolate",
#endif
};

int min_free_kbytes = 1024;
int user_min_free_kbytes = -1;
static int watermark_boost_factor __read_mostly = 15000;
static int watermark_scale_factor = 10;

/* movable_zone is the "real" zone pages in ZONE_MOVABLE are taken from */
int movable_zone;
EXPORT_SYMBOL(movable_zone);

#if MAX_NUMNODES > 1
unsigned int nr_node_ids __read_mostly = MAX_NUMNODES;
unsigned int nr_online_nodes __read_mostly = 1;
EXPORT_SYMBOL(nr_node_ids);
EXPORT_SYMBOL(nr_online_nodes);
#endif

static bool page_contains_unaccepted(struct page *page, unsigned int order);
static void accept_page(struct page *page, unsigned int order);
static bool try_to_accept_memory(struct zone *zone, unsigned int order);
static inline bool has_unaccepted_memory(void);
static bool __free_unaccepted(struct page *page);

int page_group_by_mobility_disabled __read_mostly;

#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
/*
 * During boot we initialize deferred pages on-demand, as needed, but once
 * page_alloc_init_late() has finished, the deferred pages are all initialized,
 * and we can permanently disable that path.
 */
DEFINE_STATIC_KEY_TRUE(deferred_pages);

static inline bool deferred_pages_enabled(void)
{
	return static_branch_unlikely(&deferred_pages);
}

/*
 * deferred_grow_zone() is __init, but it is called from
 * get_page_from_freelist() during early boot until deferred_pages permanently
 * disables this call. This is why we have refdata wrapper to avoid warning,
 * and to ensure that the function body gets unloaded.
 */
static bool __ref
_deferred_grow_zone(struct zone *zone, unsigned int order)
{
	return deferred_grow_zone(zone, order);
}
#else
static inline bool deferred_pages_enabled(void)
{
	return false;
}
#endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */

/* Return a pointer to the bitmap storing bits affecting a block of pages */
static inline unsigned long *get_pageblock_bitmap(const struct page *page,
							unsigned long pfn)
{
#ifdef CONFIG_SPARSEMEM
	return section_to_usemap(__pfn_to_section(pfn));
#else
	return page_zone(page)->pageblock_flags;
#endif /* CONFIG_SPARSEMEM */
}

static inline int pfn_to_bitidx(const struct page *page, unsigned long pfn)
{
#ifdef CONFIG_SPARSEMEM
	pfn &= (PAGES_PER_SECTION-1);
#else
	pfn = pfn - pageblock_start_pfn(page_zone(page)->zone_start_pfn);
#endif /* CONFIG_SPARSEMEM */
	return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS;
}

/**
 * get_pfnblock_flags_mask - Return the requested group of flags for the pageblock_nr_pages block of pages
 * @page: The page within the block of interest
 * @pfn: The target page frame number
 * @mask: mask of bits that the caller is interested in
 *
 * Return: pageblock_bits flags
 */
unsigned long get_pfnblock_flags_mask(const struct page *page,
					unsigned long pfn, unsigned long mask)
{
	unsigned long *bitmap;
	unsigned long bitidx, word_bitidx;
	unsigned long word;

	bitmap = get_pageblock_bitmap(page, pfn);
	bitidx = pfn_to_bitidx(page, pfn);
	word_bitidx = bitidx / BITS_PER_LONG;
	bitidx &= (BITS_PER_LONG-1);
	/*
	 * This races, without locks, with set_pfnblock_flags_mask(). Ensure
	 * a consistent read of the memory array, so that results, even though
	 * racy, are not corrupted.
	 */
	word = READ_ONCE(bitmap[word_bitidx]);
	return (word >> bitidx) & mask;
}

static __always_inline int get_pfnblock_migratetype(const struct page *page,
					unsigned long pfn)
{
	return get_pfnblock_flags_mask(page, pfn, MIGRATETYPE_MASK);
}

/**
 * set_pfnblock_flags_mask - Set the requested group of flags for a pageblock_nr_pages block of pages
 * @page: The page within the block of interest
 * @flags: The flags to set
 * @pfn: The target page frame number
 * @mask: mask of bits that the caller is interested in
 */
void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
					unsigned long pfn,
					unsigned long mask)
{
	unsigned long *bitmap;
	unsigned long bitidx, word_bitidx;
	unsigned long word;

	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
	BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits));

	bitmap = get_pageblock_bitmap(page, pfn);
	bitidx = pfn_to_bitidx(page, pfn);
	word_bitidx = bitidx / BITS_PER_LONG;
	bitidx &= (BITS_PER_LONG-1);

	VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);

	mask <<= bitidx;
	flags <<= bitidx;

	word = READ_ONCE(bitmap[word_bitidx]);
	do {
	} while (!try_cmpxchg(&bitmap[word_bitidx], &word, (word & ~mask) | flags));
}

void set_pageblock_migratetype(struct page *page, int migratetype)
{
	if (unlikely(page_group_by_mobility_disabled &&
		     migratetype < MIGRATE_PCPTYPES))
		migratetype = MIGRATE_UNMOVABLE;

	set_pfnblock_flags_mask(page, (unsigned long)migratetype,
				page_to_pfn(page), MIGRATETYPE_MASK);
}

#ifdef CONFIG_DEBUG_VM
static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
{
	int ret;
	unsigned seq;
	unsigned long pfn = page_to_pfn(page);
	unsigned long sp, start_pfn;

	do {
		seq = zone_span_seqbegin(zone);
		start_pfn = zone->zone_start_pfn;
		sp = zone->spanned_pages;
		ret = !zone_spans_pfn(zone, pfn);
	} while (zone_span_seqretry(zone, seq));

	if (ret)
		pr_err("page 0x%lx outside node %d zone %s [ 0x%lx - 0x%lx ]\n",
			pfn, zone_to_nid(zone), zone->name,
			start_pfn, start_pfn + sp);

	return ret;
}

/*
 * Temporary debugging check for pages not lying within a given zone.
 */
static bool __maybe_unused bad_range(struct zone *zone, struct page *page)
{
	if (page_outside_zone_boundaries(zone, page))
		return true;
	if (zone != page_zone(page))
		return true;

	return false;
}
#else
static inline bool __maybe_unused bad_range(struct zone *zone, struct page *page)
{
	return false;
}
#endif

static void bad_page(struct page *page, const char *reason)
{
	static unsigned long resume;
	static unsigned long nr_shown;
	static unsigned long nr_unshown;

	/*
	 * Allow a burst of 60 reports, then keep quiet for that minute;
	 * or allow a steady drip of one report per second.
	 */
	if (nr_shown == 60) {
		if (time_before(jiffies, resume)) {
			nr_unshown++;
			goto out;
		}
		if (nr_unshown) {
			pr_alert(
			      "BUG: Bad page state: %lu messages suppressed\n",
				nr_unshown);
			nr_unshown = 0;
		}
		nr_shown = 0;
	}
	if (nr_shown++ == 0)
		resume = jiffies + 60 * HZ;

	pr_alert("BUG: Bad page state in process %s  pfn:%05lx\n",
		current->comm, page_to_pfn(page));
	dump_page(page, reason);

	print_modules();
	dump_stack();
out:
	/* Leave bad fields for debug, except PageBuddy could make trouble */
	page_mapcount_reset(page); /* remove PageBuddy */
	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
}

static inline unsigned int order_to_pindex(int migratetype, int order)
{
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	if (order > PAGE_ALLOC_COSTLY_ORDER) {
		VM_BUG_ON(order != HPAGE_PMD_ORDER);
		return NR_LOWORDER_PCP_LISTS;
	}
#else
	VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
#endif

	return (MIGRATE_PCPTYPES * order) + migratetype;
}

static inline int pindex_to_order(unsigned int pindex)
{
	int order = pindex / MIGRATE_PCPTYPES;

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	if (pindex == NR_LOWORDER_PCP_LISTS)
		order = HPAGE_PMD_ORDER;
#else
	VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
#endif

	return order;
}

static inline bool pcp_allowed_order(unsigned int order)
{
	if (order <= PAGE_ALLOC_COSTLY_ORDER)
		return true;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	if (order == HPAGE_PMD_ORDER)
		return true;
#endif
	return false;
}

/*
 * Higher-order pages are called "compound pages".  They are structured thusly:
 *
 * The first PAGE_SIZE page is called the "head page" and have PG_head set.
 *
 * The remaining PAGE_SIZE pages are called "tail pages". PageTail() is encoded
 * in bit 0 of page->compound_head. The rest of bits is pointer to head page.
 *
 * The first tail page's ->compound_order holds the order of allocation.
 * This usage means that zero-order pages may not be compound.
 */

void prep_compound_page(struct page *page, unsigned int order)
{
	int i;
	int nr_pages = 1 << order;

	__SetPageHead(page);
	for (i = 1; i < nr_pages; i++)
		prep_compound_tail(page, i);

	prep_compound_head(page, order);
}

static inline void set_buddy_order(struct page *page, unsigned int order)
{
	set_page_private(page, order);
	__SetPageBuddy(page);
}

#ifdef CONFIG_COMPACTION
static inline struct capture_control *task_capc(struct zone *zone)
{
	struct capture_control *capc = current->capture_control;

	return unlikely(capc) &&
		!(current->flags & PF_KTHREAD) &&
		!capc->page &&
		capc->cc->zone == zone ? capc : NULL;
}

static inline bool
compaction_capture(struct capture_control *capc, struct page *page,
		   int order, int migratetype)
{
	if (!capc || order != capc->cc->order)
		return false;

	/* Do not accidentally pollute CMA or isolated regions*/
	if (is_migrate_cma(migratetype) ||
	    is_migrate_isolate(migratetype))
		return false;

	/*
	 * Do not let lower order allocations pollute a movable pageblock
	 * unless compaction is also requesting movable pages.
	 * This might let an unmovable request use a reclaimable pageblock
	 * and vice-versa but no more than normal fallback logic which can
	 * have trouble finding a high-order free page.
	 */
	if (order < pageblock_order && migratetype == MIGRATE_MOVABLE &&
	    capc->cc->migratetype != MIGRATE_MOVABLE)
		return false;

	capc->page = page;
	return true;
}

#else
static inline struct capture_control *task_capc(struct zone *zone)
{
	return NULL;
}

static inline bool
compaction_capture(struct capture_control *capc, struct page *page,
		   int order, int migratetype)
{
	return false;
}
#endif /* CONFIG_COMPACTION */

static inline void account_freepages(struct zone *zone, int nr_pages,
				     int migratetype)
{
	if (is_migrate_isolate(migratetype))
		return;

	__mod_zone_page_state(zone, NR_FREE_PAGES, nr_pages);

	if (is_migrate_cma(migratetype))
		__mod_zone_page_state(zone, NR_FREE_CMA_PAGES, nr_pages);
}

/* Used for pages not on another list */
static inline void __add_to_free_list(struct page *page, struct zone *zone,
				      unsigned int order, int migratetype,
				      bool tail)
{
	struct free_area *area = &zone->free_area[order];

	VM_WARN_ONCE(get_pageblock_migratetype(page) != migratetype,
		     "page type is %lu, passed migratetype is %d (nr=%d)\n",
		     get_pageblock_migratetype(page), migratetype, 1 << order);

	if (tail)
		list_add_tail(&page->buddy_list, &area->free_list[migratetype]);
	else
		list_add(&page->buddy_list, &area->free_list[migratetype]);
	area->nr_free++;
}

/*
 * Used for pages which are on another list. Move the pages to the tail
 * of the list - so the moved pages won't immediately be considered for
 * allocation again (e.g., optimization for memory onlining).
 */
static inline void move_to_free_list(struct page *page, struct zone *zone,
				     unsigned int order, int old_mt, int new_mt)
{
	struct free_area *area = &zone->free_area[order];

	/* Free page moving can fail, so it happens before the type update */
	VM_WARN_ONCE(get_pageblock_migratetype(page) != old_mt,
		     "page type is %lu, passed migratetype is %d (nr=%d)\n",
		     get_pageblock_migratetype(page), old_mt, 1 << order);

	list_move_tail(&page->buddy_list, &area->free_list[new_mt]);

	account_freepages(zone, -(1 << order), old_mt);
	account_freepages(zone, 1 << order, new_mt);
}

static inline void __del_page_from_free_list(struct page *page, struct zone *zone,
					     unsigned int order, int migratetype)
{
        VM_WARN_ONCE(get_pageblock_migratetype(page) != migratetype,
		     "page type is %lu, passed migratetype is %d (nr=%d)\n",
		     get_pageblock_migratetype(page), migratetype, 1 << order);

	/* clear reported state and update reported page count */
	if (page_reported(page))
		__ClearPageReported(page);

	list_del(&page->buddy_list);
	__ClearPageBuddy(page);
	set_page_private(page, 0);
	zone->free_area[order].nr_free--;
}

static inline void del_page_from_free_list(struct page *page, struct zone *zone,
					   unsigned int order, int migratetype)
{
	__del_page_from_free_list(page, zone, order, migratetype);
	account_freepages(zone, -(1 << order), migratetype);
}

static inline struct page *get_page_from_free_area(struct free_area *area,
					    int migratetype)
{
	return list_first_entry_or_null(&area->free_list[migratetype],
					struct page, buddy_list);
}

/*
 * If this is not the largest possible page, check if the buddy
 * of the next-highest order is free. If it is, it's possible
 * that pages are being freed that will coalesce soon. In case,
 * that is happening, add the free page to the tail of the list
 * so it's less likely to be used soon and more likely to be merged
 * as a higher order page
 */
static inline bool
buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn,
		   struct page *page, unsigned int order)
{
	unsigned long higher_page_pfn;
	struct page *higher_page;

	if (order >= MAX_PAGE_ORDER - 1)
		return false;

	higher_page_pfn = buddy_pfn & pfn;
	higher_page = page + (higher_page_pfn - pfn);

	return find_buddy_page_pfn(higher_page, higher_page_pfn, order + 1,
			NULL) != NULL;
}

/*
 * Freeing function for a buddy system allocator.
 *
 * The concept of a buddy system is to maintain direct-mapped table
 * (containing bit values) for memory blocks of various "orders".
 * The bottom level table contains the map for the smallest allocatable
 * units of memory (here, pages), and each level above it describes
 * pairs of units from the levels below, hence, "buddies".
 * At a high level, all that happens here is marking the table entry
 * at the bottom level available, and propagating the changes upward
 * as necessary, plus some accounting needed to play nicely with other
 * parts of the VM system.
 * At each level, we keep a list of pages, which are heads of continuous
 * free pages of length of (1 << order) and marked with PageBuddy.
 * Page's order is recorded in page_private(page) field.
 * So when we are allocating or freeing one, we can derive the state of the
 * other.  That is, if we allocate a small block, and both were
 * free, the remainder of the region must be split into blocks.
 * If a block is freed, and its buddy is also free, then this
 * triggers coalescing into a block of larger size.
 *
 * -- nyc
 */

static inline void __free_one_page(struct page *page,
		unsigned long pfn,
		struct zone *zone, unsigned int order,
		int migratetype, fpi_t fpi_flags)
{
	struct capture_control *capc = task_capc(zone);
	unsigned long buddy_pfn = 0;
	unsigned long combined_pfn;
	struct page *buddy;
	bool to_tail;

	VM_BUG_ON(!zone_is_initialized(zone));
	VM_BUG_ON_PAGE(page->flags & PAGE_FLAGS_CHECK_AT_PREP, page);

	VM_BUG_ON(migratetype == -1);
	VM_BUG_ON_PAGE(pfn & ((1 << order) - 1), page);
	VM_BUG_ON_PAGE(bad_range(zone, page), page);

	account_freepages(zone, 1 << order, migratetype);

	while (order < MAX_PAGE_ORDER) {
		int buddy_mt = migratetype;

		if (compaction_capture(capc, page, order, migratetype)) {
			account_freepages(zone, -(1 << order), migratetype);
			return;
		}

		buddy = find_buddy_page_pfn(page, pfn, order, &buddy_pfn);
		if (!buddy)
			goto done_merging;

		if (unlikely(order >= pageblock_order)) {
			/*
			 * We want to prevent merge between freepages on pageblock
			 * without fallbacks and normal pageblock. Without this,
			 * pageblock isolation could cause incorrect freepage or CMA
			 * accounting or HIGHATOMIC accounting.
			 */
			buddy_mt = get_pfnblock_migratetype(buddy, buddy_pfn);

			if (migratetype != buddy_mt &&
			    (!migratetype_is_mergeable(migratetype) ||
			     !migratetype_is_mergeable(buddy_mt)))
				goto done_merging;
		}

		/*
		 * Our buddy is free or it is CONFIG_DEBUG_PAGEALLOC guard page,
		 * merge with it and move up one order.
		 */
		if (page_is_guard(buddy))
			clear_page_guard(zone, buddy, order);
		else
			__del_page_from_free_list(buddy, zone, order, buddy_mt);

		if (unlikely(buddy_mt != migratetype)) {
			/*
			 * Match buddy type. This ensures that an
			 * expand() down the line puts the sub-blocks
			 * on the right freelists.
			 */
			set_pageblock_migratetype(buddy, migratetype);
		}

		combined_pfn = buddy_pfn & pfn;
		page = page + (combined_pfn - pfn);
		pfn = combined_pfn;
		order++;
	}

done_merging:
	set_buddy_order(page, order);

	if (fpi_flags & FPI_TO_TAIL)
		to_tail = true;
	else if (is_shuffle_order(order))
		to_tail = shuffle_pick_tail();
	else
		to_tail = buddy_merge_likely(pfn, buddy_pfn, page, order);

	__add_to_free_list(page, zone, order, migratetype, to_tail);

	/* Notify page reporting subsystem of freed page */
	if (!(fpi_flags & FPI_SKIP_REPORT_NOTIFY))
		page_reporting_notify_free(order);
}

/*
 * A bad page could be due to a number of fields. Instead of multiple branches,
 * try and check multiple fields with one check. The caller must do a detailed
 * check if necessary.
 */
static inline bool page_expected_state(struct page *page,
					unsigned long check_flags)
{
	if (unlikely(atomic_read(&page->_mapcount) != -1))
		return false;

	if (unlikely((unsigned long)page->mapping |
			page_ref_count(page) |
#ifdef CONFIG_MEMCG
			page->memcg_data |
#endif
#ifdef CONFIG_PAGE_POOL
			((page->pp_magic & ~0x3UL) == PP_SIGNATURE) |
#endif
			(page->flags & check_flags)))
		return false;

	return true;
}

static const char *page_bad_reason(struct page *page, unsigned long flags)
{
	const char *bad_reason = NULL;

	if (unlikely(atomic_read(&page->_mapcount) != -1))
		bad_reason = "nonzero mapcount";
	if (unlikely(page->mapping != NULL))
		bad_reason = "non-NULL mapping";
	if (unlikely(page_ref_count(page) != 0))
		bad_reason = "nonzero _refcount";
	if (unlikely(page->flags & flags)) {
		if (flags == PAGE_FLAGS_CHECK_AT_PREP)
			bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag(s) set";
		else
			bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
	}
#ifdef CONFIG_MEMCG
	if (unlikely(page->memcg_data))
		bad_reason = "page still charged to cgroup";
#endif
#ifdef CONFIG_PAGE_POOL
	if (unlikely((page->pp_magic & ~0x3UL) == PP_SIGNATURE))
		bad_reason = "page_pool leak";
#endif
	return bad_reason;
}

static void free_page_is_bad_report(struct page *page)
{
	bad_page(page,
		 page_bad_reason(page, PAGE_FLAGS_CHECK_AT_FREE));
}

static inline bool free_page_is_bad(struct page *page)
{
	if (likely(page_expected_state(page, PAGE_FLAGS_CHECK_AT_FREE)))
		return false;

	/* Something has gone sideways, find it */
	free_page_is_bad_report(page);
	return true;
}

static inline bool is_check_pages_enabled(void)
{
	return static_branch_unlikely(&check_pages_enabled);
}

static int free_tail_page_prepare(struct page *head_page, struct page *page)
{
	struct folio *folio = (struct folio *)head_page;
	int ret = 1;

	/*
	 * We rely page->lru.next never has bit 0 set, unless the page
	 * is PageTail(). Let's make sure that's true even for poisoned ->lru.
	 */
	BUILD_BUG_ON((unsigned long)LIST_POISON1 & 1);

	if (!is_check_pages_enabled()) {
		ret = 0;
		goto out;
	}
	switch (page - head_page) {
	case 1:
		/* the first tail page: these may be in place of ->mapping */
		if (unlikely(folio_entire_mapcount(folio))) {
			bad_page(page, "nonzero entire_mapcount");
			goto out;
		}
		if (unlikely(folio_large_mapcount(folio))) {
			bad_page(page, "nonzero large_mapcount");
			goto out;
		}
		if (unlikely(atomic_read(&folio->_nr_pages_mapped))) {
			bad_page(page, "nonzero nr_pages_mapped");
			goto out;
		}
		if (unlikely(atomic_read(&folio->_pincount))) {
			bad_page(page, "nonzero pincount");
			goto out;
		}
		break;
	case 2:
		/* the second tail page: deferred_list overlaps ->mapping */
		if (unlikely(!list_empty(&folio->_deferred_list))) {
			bad_page(page, "on deferred list");
			goto out;
		}
		break;
	default:
		if (page->mapping != TAIL_MAPPING) {
			bad_page(page, "corrupted mapping in tail page");
			goto out;
		}
		break;
	}
	if (unlikely(!PageTail(page))) {
		bad_page(page, "PageTail not set");
		goto out;
	}
	if (unlikely(compound_head(page) != head_page)) {
		bad_page(page, "compound_head not consistent");
		goto out;
	}
	ret = 0;
out:
	page->mapping = NULL;
	clear_compound_head(page);
	return ret;
}

/*
 * Skip KASAN memory poisoning when either:
 *
 * 1. For generic KASAN: deferred memory initialization has not yet completed.
 *    Tag-based KASAN modes skip pages freed via deferred memory initialization
 *    using page tags instead (see below).
 * 2. For tag-based KASAN modes: the page has a match-all KASAN tag, indicating
 *    that error detection is disabled for accesses via the page address.
 *
 * Pages will have match-all tags in the following circumstances:
 *
 * 1. Pages are being initialized for the first time, including during deferred
 *    memory init; see the call to page_kasan_tag_reset in __init_single_page.
 * 2. The allocation was not unpoisoned due to __GFP_SKIP_KASAN, with the
 *    exception of pages unpoisoned by kasan_unpoison_vmalloc.
 * 3. The allocation was excluded from being checked due to sampling,
 *    see the call to kasan_unpoison_pages.
 *
 * Poisoning pages during deferred memory init will greatly lengthen the
 * process and cause problem in large memory systems as the deferred pages
 * initialization is done with interrupt disabled.
 *
 * Assuming that there will be no reference to those newly initialized
 * pages before they are ever allocated, this should have no effect on
 * KASAN memory tracking as the poison will be properly inserted at page
 * allocation time. The only corner case is when pages are allocated by
 * on-demand allocation and then freed again before the deferred pages
 * initialization is done, but this is not likely to happen.
 */
static inline bool should_skip_kasan_poison(struct page *page)
{
	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
		return deferred_pages_enabled();

	return page_kasan_tag(page) == KASAN_TAG_KERNEL;
}

void kernel_init_pages(struct page *page, int numpages)
{
	int i;

	/* s390's use of memset() could override KASAN redzones. */
	kasan_disable_current();
	for (i = 0; i < numpages; i++)
		clear_highpage_kasan_tagged(page + i);
	kasan_enable_current();
}

__always_inline bool free_pages_prepare(struct page *page,
			unsigned int order)
{
	int bad = 0;
	bool skip_kasan_poison = should_skip_kasan_poison(page);
	bool init = want_init_on_free();
	bool compound = PageCompound(page);

	VM_BUG_ON_PAGE(PageTail(page), page);

	trace_mm_page_free(page, order);
	kmsan_free_page(page, order);

	if (memcg_kmem_online() && PageMemcgKmem(page))
		__memcg_kmem_uncharge_page(page, order);

	if (unlikely(PageHWPoison(page)) && !order) {
		/* Do not let hwpoison pages hit pcplists/buddy */
		reset_page_owner(page, order);
		page_table_check_free(page, order);
		pgalloc_tag_sub(page, 1 << order);
		return false;
	}

	VM_BUG_ON_PAGE(compound && compound_order(page) != order, page);

	/*
	 * Check tail pages before head page information is cleared to
	 * avoid checking PageCompound for order-0 pages.
	 */
	if (unlikely(order)) {
		int i;

		if (compound)
			page[1].flags &= ~PAGE_FLAGS_SECOND;
		for (i = 1; i < (1 << order); i++) {
			if (compound)
				bad += free_tail_page_prepare(page, page + i);
			if (is_check_pages_enabled()) {
				if (free_page_is_bad(page + i)) {
					bad++;
					continue;
				}
			}
			(page + i)->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
		}
	}
	if (PageMappingFlags(page))
		page->mapping = NULL;
	if (is_check_pages_enabled()) {
		if (free_page_is_bad(page))
			bad++;
		if (bad)
			return false;
	}

	page_cpupid_reset_last(page);
	page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
	reset_page_owner(page, order);
	page_table_check_free(page, order);
	pgalloc_tag_sub(page, 1 << order);

	if (!PageHighMem(page)) {
		debug_check_no_locks_freed(page_address(page),
					   PAGE_SIZE << order);
		debug_check_no_obj_freed(page_address(page),
					   PAGE_SIZE << order);
	}

	kernel_poison_pages(page, 1 << order);

	/*
	 * As memory initialization might be integrated into KASAN,
	 * KASAN poisoning and memory initialization code must be
	 * kept together to avoid discrepancies in behavior.
	 *
	 * With hardware tag-based KASAN, memory tags must be set before the
	 * page becomes unavailable via debug_pagealloc or arch_free_page.
	 */
	if (!skip_kasan_poison) {
		kasan_poison_pages(page, order, init);

		/* Memory is already initialized if KASAN did it internally. */
		if (kasan_has_integrated_init())
			init = false;
	}
	if (init)
		kernel_init_pages(page, 1 << order);

	/*
	 * arch_free_page() can make the page's contents inaccessible.  s390
	 * does this.  So nothing which can access the page's contents should
	 * happen after this.
	 */
	arch_free_page(page, order);

	debug_pagealloc_unmap_pages(page, 1 << order);

	return true;
}

/*
 * Frees a number of pages from the PCP lists
 * Assumes all pages on list are in same zone.
 * count is the number of pages to free.
 */
static void free_pcppages_bulk(struct zone *zone, int count,
					struct per_cpu_pages *pcp,
					int pindex)
{
	unsigned long flags;
	unsigned int order;
	struct page *page;

	/*
	 * Ensure proper count is passed which otherwise would stuck in the
	 * below while (list_empty(list)) loop.
	 */
	count = min(pcp->count, count);

	/* Ensure requested pindex is drained first. */
	pindex = pindex - 1;

	spin_lock_irqsave(&zone->lock, flags);

	while (count > 0) {
		struct list_head *list;
		int nr_pages;

		/* Remove pages from lists in a round-robin fashion. */
		do {
			if (++pindex > NR_PCP_LISTS - 1)
				pindex = 0;
			list = &pcp->lists[pindex];
		} while (list_empty(list));

		order = pindex_to_order(pindex);
		nr_pages = 1 << order;
		do {
			unsigned long pfn;
			int mt;

			page = list_last_entry(list, struct page, pcp_list);
			pfn = page_to_pfn(page);
			mt = get_pfnblock_migratetype(page, pfn);

			/* must delete to avoid corrupting pcp list */
			list_del(&page->pcp_list);
			count -= nr_pages;
			pcp->count -= nr_pages;

			__free_one_page(page, pfn, zone, order, mt, FPI_NONE);
			trace_mm_page_pcpu_drain(page, order, mt);
		} while (count > 0 && !list_empty(list));
	}

	spin_unlock_irqrestore(&zone->lock, flags);
}

static void free_one_page(struct zone *zone, struct page *page,
			  unsigned long pfn, unsigned int order,
			  fpi_t fpi_flags)
{
	unsigned long flags;
	int migratetype;

	spin_lock_irqsave(&zone->lock, flags);
	migratetype = get_pfnblock_migratetype(page, pfn);
	__free_one_page(page, pfn, zone, order, migratetype, fpi_flags);
	spin_unlock_irqrestore(&zone->lock, flags);
}

static void __free_pages_ok(struct page *page, unsigned int order,
			    fpi_t fpi_flags)
{
	unsigned long pfn = page_to_pfn(page);
	struct zone *zone = page_zone(page);

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

	free_one_page(zone, page, pfn, order, fpi_flags);

	__count_vm_events(PGFREE, 1 << order);
}

void __free_pages_core(struct page *page, unsigned int order)
{
	unsigned int nr_pages = 1 << order;
	struct page *p = page;
	unsigned int loop;

	/*
	 * When initializing the memmap, __init_single_page() sets the refcount
	 * of all pages to 1 ("allocated"/"not free"). We have to set the
	 * refcount of all involved pages to 0.
	 */
	prefetchw(p);
	for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
		prefetchw(p + 1);
		__ClearPageReserved(p);
		set_page_count(p, 0);
	}
	__ClearPageReserved(p);
	set_page_count(p, 0);

	atomic_long_add(nr_pages, &page_zone(page)->managed_pages);

	if (page_contains_unaccepted(page, order)) {
		if (order == MAX_PAGE_ORDER && __free_unaccepted(page))
			return;

		accept_page(page, order);
	}

	/*
	 * Bypass PCP and place fresh pages right to the tail, primarily
	 * relevant for memory onlining.
	 */
	__free_pages_ok(page, order, FPI_TO_TAIL);
}

/*
 * Check that the whole (or subset of) a pageblock given by the interval of
 * [start_pfn, end_pfn) is valid and within the same zone, before scanning it
 * with the migration of free compaction scanner.
 *
 * Return struct page pointer of start_pfn, or NULL if checks were not passed.
 *
 * 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. We assume that a border between node0 and node1
 * can occur within a single pageblock, but not a node0 node1 node0
 * interleaving within a single pageblock. It is therefore sufficient to check
 * the first and last page of a pageblock and avoid checking each individual
 * page in a pageblock.
 *
 * Note: the function may return non-NULL struct page even for a page block
 * which contains a memory hole (i.e. there is no physical memory for a subset
 * of the pfn range). For example, if the pageblock order is MAX_PAGE_ORDER, which
 * will fall into 2 sub-sections, and the end pfn of the pageblock may be hole
 * even though the start pfn is online and valid. This should be safe most of
 * the time because struct pages are still initialized via init_unavailable_range()
 * and pfn walkers shouldn't touch any physical memory range for which they do
 * not recognize any specific metadata in struct pages.
 */
struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
				     unsigned long end_pfn, struct zone *zone)
{
	struct page *start_page;
	struct page *end_page;

	/* end_pfn is one past the range we are checking */
	end_pfn--;

	if (!pfn_valid(end_pfn))
		return NULL;

	start_page = pfn_to_online_page(start_pfn);
	if (!start_page)
		return NULL;

	if (page_zone(start_page) != zone)
		return NULL;

	end_page = pfn_to_page(end_pfn);

	/* This gives a shorter code than deriving page_zone(end_page) */
	if (page_zone_id(start_page) != page_zone_id(end_page))
		return NULL;

	return start_page;
}

/*
 * The order of subdivision here is critical for the IO subsystem.
 * Please do not alter this order without good reasons and regression
 * testing. Specifically, as large blocks of memory are subdivided,
 * the order in which smaller blocks are delivered depends on the order
 * they're subdivided in this function. This is the primary factor
 * influencing the order in which pages are delivered to the IO
 * subsystem according to empirical testing, and this is also justified
 * by considering the behavior of a buddy system containing a single
 * large block of memory acted on by a series of small allocations.
 * This behavior is a critical factor in sglist merging's success.
 *
 * -- nyc
 */
static inline void expand(struct zone *zone, struct page *page,
	int low, int high, int migratetype)
{
	unsigned long size = 1 << high;
	unsigned long nr_added = 0;

	while (high > low) {
		high--;
		size >>= 1;
		VM_BUG_ON_PAGE(bad_range(zone, &page[size]), &page[size]);

		/*
		 * Mark as guard pages (or page), that will allow to
		 * merge back to allocator when buddy will be freed.
		 * Corresponding page table entries will not be touched,
		 * pages will stay not present in virtual address space
		 */
		if (set_page_guard(zone, &page[size], high))
			continue;

		__add_to_free_list(&page[size], zone, high, migratetype, false);
		set_buddy_order(&page[size], high);
		nr_added += size;
	}
	account_freepages(zone, nr_added, migratetype);
}

static void check_new_page_bad(struct page *page)
{
	if (unlikely(page->flags & __PG_HWPOISON)) {
		/* Don't complain about hwpoisoned pages */
		page_mapcount_reset(page); /* remove PageBuddy */
		return;
	}

	bad_page(page,
		 page_bad_reason(page, PAGE_FLAGS_CHECK_AT_PREP));
}

/*
 * This page is about to be returned from the page allocator
 */
static bool check_new_page(struct page *page)
{
	if (likely(page_expected_state(page,
				PAGE_FLAGS_CHECK_AT_PREP|__PG_HWPOISON)))
		return false;

	check_new_page_bad(page);
	return true;
}

static inline bool check_new_pages(struct page *page, unsigned int order)
{
	if (is_check_pages_enabled()) {
		for (int i = 0; i < (1 << order); i++) {
			struct page *p = page + i;

			if (check_new_page(p))
				return true;
		}
	}

	return false;
}

static inline bool should_skip_kasan_unpoison(gfp_t flags)
{
	/* Don't skip if a software KASAN mode is enabled. */
	if (IS_ENABLED(CONFIG_KASAN_GENERIC) ||
	    IS_ENABLED(CONFIG_KASAN_SW_TAGS))
		return false;

	/* Skip, if hardware tag-based KASAN is not enabled. */
	if (!kasan_hw_tags_enabled())
		return true;

	/*
	 * With hardware tag-based KASAN enabled, skip if this has been
	 * requested via __GFP_SKIP_KASAN.
	 */
	return flags & __GFP_SKIP_KASAN;
}

static inline bool should_skip_init(gfp_t flags)
{
	/* Don't skip, if hardware tag-based KASAN is not enabled. */
	if (!kasan_hw_tags_enabled())
		return false;

	/* For hardware tag-based KASAN, skip if requested. */
	return (flags & __GFP_SKIP_ZERO);
}

inline void post_alloc_hook(struct page *page, unsigned int order,
				gfp_t gfp_flags)
{
	bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags) &&
			!should_skip_init(gfp_flags);
	bool zero_tags = init && (gfp_flags & __GFP_ZEROTAGS);
	int i;

	set_page_private(page, 0);
	set_page_refcounted(page);

	arch_alloc_page(page, order);
	debug_pagealloc_map_pages(page, 1 << order);

	/*
	 * Page unpoisoning must happen before memory initialization.
	 * Otherwise, the poison pattern will be overwritten for __GFP_ZERO
	 * allocations and the page unpoisoning code will complain.
	 */
	kernel_unpoison_pages(page, 1 << order);

	/*
	 * As memory initialization might be integrated into KASAN,
	 * KASAN unpoisoning and memory initializion code must be
	 * kept together to avoid discrepancies in behavior.
	 */

	/*
	 * If memory tags should be zeroed
	 * (which happens only when memory should be initialized as well).
	 */
	if (zero_tags) {
		/* Initialize both memory and memory tags. */
		for (i = 0; i != 1 << order; ++i)
			tag_clear_highpage(page + i);

		/* Take note that memory was initialized by the loop above. */
		init = false;
	}
	if (!should_skip_kasan_unpoison(gfp_flags) &&
	    kasan_unpoison_pages(page, order, init)) {
		/* Take note that memory was initialized by KASAN. */
		if (kasan_has_integrated_init())
			init = false;
	} else {
		/*
		 * If memory tags have not been set by KASAN, reset the page
		 * tags to ensure page_address() dereferencing does not fault.
		 */
		for (i = 0; i != 1 << order; ++i)
			page_kasan_tag_reset(page + i);
	}
	/* If memory is still not initialized, initialize it now. */
	if (init)
		kernel_init_pages(page, 1 << order);

	set_page_owner(page, order, gfp_flags);
	page_table_check_alloc(page, order);
	pgalloc_tag_add(page, current, 1 << order);
}

static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
							unsigned int alloc_flags)
{
	post_alloc_hook(page, order, gfp_flags);

	if (order && (gfp_flags & __GFP_COMP))
		prep_compound_page(page, order);

	/*
	 * page is set pfmemalloc 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.
	 */
	if (alloc_flags & ALLOC_NO_WATERMARKS)
		set_page_pfmemalloc(page);
	else
		clear_page_pfmemalloc(page);
}

/*
 * Go through the free lists for the given migratetype and remove
 * the smallest available page from the freelists
 */
static __always_inline
struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
						int migratetype)
{
	unsigned int current_order;
	struct free_area *area;
	struct page *page;

	/* Find a page of the appropriate size in the preferred list */
	for (current_order = order; current_order < NR_PAGE_ORDERS; ++current_order) {
		area = &(zone->free_area[current_order]);
		page = get_page_from_free_area(area, migratetype);
		if (!page)
			continue;
		del_page_from_free_list(page, zone, current_order, migratetype);
		expand(zone, page, order, current_order, migratetype);
		trace_mm_page_alloc_zone_locked(page, order, migratetype,
				pcp_allowed_order(order) &&
				migratetype < MIGRATE_PCPTYPES);
		return page;
	}

	return NULL;
}


/*
 * This array describes the order lists are fallen back to when
 * the free lists for the desirable migrate type are depleted
 *
 * The other migratetypes do not have fallbacks.
 */
static int fallbacks[MIGRATE_PCPTYPES][MIGRATE_PCPTYPES - 1] = {
	[MIGRATE_UNMOVABLE]   = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE   },
	[MIGRATE_MOVABLE]     = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE },
	[MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE,   MIGRATE_MOVABLE   },
};

#ifdef CONFIG_CMA
static __always_inline struct page *__rmqueue_cma_fallback(struct zone *zone,
					unsigned int order)
{
	return __rmqueue_smallest(zone, order, MIGRATE_CMA);
}
#else
static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
					unsigned int order) { return NULL; }
#endif

/*
 * Change the type of a block and move all its free pages to that
 * type's freelist.
 */
static int __move_freepages_block(struct zone *zone, unsigned long start_pfn,
				  int old_mt, int new_mt)
{
	struct page *page;
	unsigned long pfn, end_pfn;
	unsigned int order;
	int pages_moved = 0;

	VM_WARN_ON(start_pfn & (pageblock_nr_pages - 1));
	end_pfn = pageblock_end_pfn(start_pfn);

	for (pfn = start_pfn; pfn < end_pfn;) {
		page = pfn_to_page(pfn);
		if (!PageBuddy(page)) {
			pfn++;
			continue;
		}

		/* Make sure we are not inadvertently changing nodes */
		VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page);
		VM_BUG_ON_PAGE(page_zone(page) != zone, page);

		order = buddy_order(page);

		move_to_free_list(page, zone, order, old_mt, new_mt);

		pfn += 1 << order;
		pages_moved += 1 << order;
	}

	set_pageblock_migratetype(pfn_to_page(start_pfn), new_mt);

	return pages_moved;
}

static bool prep_move_freepages_block(struct zone *zone, struct page *page,
				      unsigned long *start_pfn,
				      int *num_free, int *num_movable)
{
	unsigned long pfn, start, end;

	pfn = page_to_pfn(page);
	start = pageblock_start_pfn(pfn);
	end = pageblock_end_pfn(pfn);

	/*
	 * The caller only has the lock for @zone, don't touch ranges
	 * that straddle into other zones. While we could move part of
	 * the range that's inside the zone, this call is usually
	 * accompanied by other operations such as migratetype updates
	 * which also should be locked.
	 */
	if (!zone_spans_pfn(zone, start))
		return false;
	if (!zone_spans_pfn(zone, end - 1))
		return false;

	*start_pfn = start;

	if (num_free) {
		*num_free = 0;
		*num_movable = 0;
		for (pfn = start; pfn < end;) {
			page = pfn_to_page(pfn);
			if (PageBuddy(page)) {
				int nr = 1 << buddy_order(page);

				*num_free += nr;
				pfn += nr;
				continue;
			}
			/*
			 * We assume that pages that could be isolated for
			 * migration are movable. But we don't actually try
			 * isolating, as that would be expensive.
			 */
			if (PageLRU(page) || __PageMovable(page))
				(*num_movable)++;
			pfn++;
		}
	}

	return true;
}

static int move_freepages_block(struct zone *zone, struct page *page,
				int old_mt, int new_mt)
{
	unsigned long start_pfn;

	if (!prep_move_freepages_block(zone, page, &start_pfn, NULL, NULL))
		return -1;

	return __move_freepages_block(zone, start_pfn, old_mt, new_mt);
}

#ifdef CONFIG_MEMORY_ISOLATION
/* Look for a buddy that straddles start_pfn */
static unsigned long find_large_buddy(unsigned long start_pfn)
{
	int order = 0;
	struct page *page;
	unsigned long pfn = start_pfn;

	while (!PageBuddy(page = pfn_to_page(pfn))) {
		/* Nothing found */
		if (++order > MAX_PAGE_ORDER)
			return start_pfn;
		pfn &= ~0UL << order;
	}

	/*
	 * Found a preceding buddy, but does it straddle?
	 */
	if (pfn + (1 << buddy_order(page)) > start_pfn)
		return pfn;

	/* Nothing found */
	return start_pfn;
}

/* Split a multi-block free page into its individual pageblocks */
static void split_large_buddy(struct zone *zone, struct page *page,
			      unsigned long pfn, int order)
{
	unsigned long end_pfn = pfn + (1 << order);

	VM_WARN_ON_ONCE(order <= pageblock_order);
	VM_WARN_ON_ONCE(pfn & (pageblock_nr_pages - 1));

	/* Caller removed page from freelist, buddy info cleared! */
	VM_WARN_ON_ONCE(PageBuddy(page));

	while (pfn != end_pfn) {
		int mt = get_pfnblock_migratetype(page, pfn);

		__free_one_page(page, pfn, zone, pageblock_order, mt, FPI_NONE);
		pfn += pageblock_nr_pages;
		page = pfn_to_page(pfn);
	}
}

/**
 * move_freepages_block_isolate - move free pages in block for page isolation
 * @zone: the zone
 * @page: the pageblock page
 * @migratetype: migratetype to set on the pageblock
 *
 * This is similar to move_freepages_block(), but handles the special
 * case encountered in page isolation, where the block of interest
 * might be part of a larger buddy spanning multiple pageblocks.
 *
 * Unlike the regular page allocator path, which moves pages while
 * stealing buddies off the freelist, page isolation is interested in
 * arbitrary pfn ranges that may have overlapping buddies on both ends.
 *
 * This function handles that. Straddling buddies are split into
 * individual pageblocks. Only the block of interest is moved.
 *
 * Returns %true if pages could be moved, %false otherwise.
 */
bool move_freepages_block_isolate(struct zone *zone, struct page *page,
				  int migratetype)
{
	unsigned long start_pfn, pfn;

	if (!prep_move_freepages_block(zone, page, &start_pfn, NULL, NULL))
		return false;

	/* No splits needed if buddies can't span multiple blocks */
	if (pageblock_order == MAX_PAGE_ORDER)
		goto move;

	/* We're a tail block in a larger buddy */
	pfn = find_large_buddy(start_pfn);
	if (pfn != start_pfn) {
		struct page *buddy = pfn_to_page(pfn);
		int order = buddy_order(buddy);

		del_page_from_free_list(buddy, zone, order,
					get_pfnblock_migratetype(buddy, pfn));
		set_pageblock_migratetype(page, migratetype);
		split_large_buddy(zone, buddy, pfn, order);
		return true;
	}

	/* We're the starting block of a larger buddy */
	if (PageBuddy(page) && buddy_order(page) > pageblock_order) {
		int order = buddy_order(page);

		del_page_from_free_list(page, zone, order,
					get_pfnblock_migratetype(page, pfn));
		set_pageblock_migratetype(page, migratetype);
		split_large_buddy(zone, page, pfn, order);
		return true;
	}
move:
	__move_freepages_block(zone, start_pfn,
			       get_pfnblock_migratetype(page, start_pfn),
			       migratetype);
	return true;
}
#endif /* CONFIG_MEMORY_ISOLATION */

static void change_pageblock_range(struct page *pageblock_page,
					int start_order, int migratetype)
{
	int nr_pageblocks = 1 << (start_order - pageblock_order);

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

/*
 * When we are falling back to another migratetype during allocation, try to
 * steal extra free pages from the same pageblocks to satisfy further
 * allocations, instead of polluting multiple pageblocks.
 *
 * If we are stealing a relatively large buddy page, it is likely there will
 * be more free pages in the pageblock, so try to steal them all. For
 * reclaimable and unmovable allocations, we steal regardless of page size,
 * as fragmentation caused by those allocations polluting movable pageblocks
 * is worse than movable allocations stealing from unmovable and reclaimable
 * pageblocks.
 */
static bool can_steal_fallback(unsigned int order, int start_mt)
{
	/*
	 * Leaving this order check is intended, although there is
	 * relaxed order check in next check. The reason is that
	 * we can actually steal whole pageblock if this condition met,
	 * but, below check doesn't guarantee it and that is just heuristic
	 * so could be changed anytime.
	 */
	if (order >= pageblock_order)
		return true;

	if (order >= pageblock_order / 2 ||
		start_mt == MIGRATE_RECLAIMABLE ||
		start_mt == MIGRATE_UNMOVABLE ||
		page_group_by_mobility_disabled)
		return true;

	return false;
}

static inline bool boost_watermark(struct zone *zone)
{
	unsigned long max_boost;

	if (!watermark_boost_factor)
		return false;
	/*
	 * Don't bother in zones that are unlikely to produce results.
	 * On small machines, including kdump capture kernels running
	 * in a small area, boosting the watermark can cause an out of
	 * memory situation immediately.
	 */
	if ((pageblock_nr_pages * 4) > zone_managed_pages(zone))
		return false;

	max_boost = mult_frac(zone->_watermark[WMARK_HIGH],
			watermark_boost_factor, 10000);

	/*
	 * high watermark may be uninitialised if fragmentation occurs
	 * very early in boot so do not boost. We do not fall
	 * through and boost by pageblock_nr_pages as failing
	 * allocations that early means that reclaim is not going
	 * to help and it may even be impossible to reclaim the
	 * boosted watermark resulting in a hang.
	 */
	if (!max_boost)
		return false;

	max_boost = max(pageblock_nr_pages, max_boost);

	zone->watermark_boost = min(zone->watermark_boost + pageblock_nr_pages,
		max_boost);

	return true;
}

/*
 * This function implements actual steal behaviour. If order is large enough, we
 * can claim the whole pageblock for the requested migratetype. If not, we check
 * the pageblock for constituent pages; if at least half of the pages are free
 * or compatible, we can still claim the whole block, so pages freed in the
 * future will be put on the correct free list. Otherwise, we isolate exactly
 * the order we need from the fallback block and leave its migratetype alone.
 */
static struct page *
steal_suitable_fallback(struct zone *zone, struct page *page,
			int current_order, int order, int start_type,
			unsigned int alloc_flags, bool whole_block)
{
	int free_pages, movable_pages, alike_pages;
	unsigned long start_pfn;
	int block_type;

	block_type = get_pageblock_migratetype(page);

	/*
	 * This can happen due to races and we want to prevent broken
	 * highatomic accounting.
	 */
	if (is_migrate_highatomic(block_type))
		goto single_page;

	/* Take ownership for orders >= pageblock_order */
	if (current_order >= pageblock_order) {
		del_page_from_free_list(page, zone, current_order, block_type);
		change_pageblock_range(page, current_order, start_type);
		expand(zone, page, order, current_order, start_type);
		return page;
	}

	/*
	 * Boost watermarks to increase reclaim pressure to reduce the
	 * likelihood of future fallbacks. Wake kswapd now as the node
	 * may be balanced overall and kswapd will not wake naturally.
	 */
	if (boost_watermark(zone) && (alloc_flags & ALLOC_KSWAPD))
		set_bit(ZONE_BOOSTED_WATERMARK, &zone->flags);

	/* We are not allowed to try stealing from the whole block */
	if (!whole_block)
		goto single_page;

	/* moving whole block can fail due to zone boundary conditions */
	if (!prep_move_freepages_block(zone, page, &start_pfn, &free_pages,
				       &movable_pages))
		goto single_page;

	/*
	 * Determine how many pages are compatible with our allocation.
	 * For movable allocation, it's the number of movable pages which
	 * we just obtained. For other types it's a bit more tricky.
	 */
	if (start_type == MIGRATE_MOVABLE) {
		alike_pages = movable_pages;
	} else {
		/*
		 * If we are falling back a RECLAIMABLE or UNMOVABLE allocation
		 * to MOVABLE pageblock, consider all non-movable pages as
		 * compatible. If it's UNMOVABLE falling back to RECLAIMABLE or
		 * vice versa, be conservative since we can't distinguish the
		 * exact migratetype of non-movable pages.
		 */
		if (block_type == MIGRATE_MOVABLE)
			alike_pages = pageblock_nr_pages
						- (free_pages + movable_pages);
		else
			alike_pages = 0;
	}
	/*
	 * If a sufficient number of pages in the block are either free or of
	 * compatible migratability as our allocation, claim the whole block.
	 */
	if (free_pages + alike_pages >= (1 << (pageblock_order-1)) ||
			page_group_by_mobility_disabled) {
		__move_freepages_block(zone, start_pfn, block_type, start_type);
		return __rmqueue_smallest(zone, order, start_type);
	}

single_page:
	del_page_from_free_list(page, zone, current_order, block_type);
	expand(zone, page, order, current_order, block_type);
	return page;
}

/*
 * Check whether there is a suitable fallback freepage with requested order.
 * If only_stealable is true, this function returns fallback_mt only if
 * we can steal other freepages all together. This would help to reduce
 * fragmentation due to mixed migratetype pages in one pageblock.
 */
int find_suitable_fallback(struct free_area *area, unsigned int order,
			int migratetype, bool only_stealable, bool *can_steal)
{
	int i;
	int fallback_mt;

	if (area->nr_free == 0)
		return -1;

	*can_steal = false;
	for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) {
		fallback_mt = fallbacks[migratetype][i];
		if (free_area_empty(area, fallback_mt))
			continue;

		if (can_steal_fallback(order, migratetype))
			*can_steal = true;

		if (!only_stealable)
			return fallback_mt;

		if (*can_steal)
			return fallback_mt;
	}

	return -1;
}

/*
 * Reserve a pageblock for exclusive use of high-order atomic allocations if
 * there are no empty page blocks that contain a page with a suitable order
 */
static void reserve_highatomic_pageblock(struct page *page, struct zone *zone)
{
	int mt;
	unsigned long max_managed, flags;

	/*
	 * The number reserved as: minimum is 1 pageblock, maximum is
	 * roughly 1% of a zone. But if 1% of a zone falls below a
	 * pageblock size, then don't reserve any pageblocks.
	 * Check is race-prone but harmless.
	 */
	if ((zone_managed_pages(zone) / 100) < pageblock_nr_pages)
		return;
	max_managed = ALIGN((zone_managed_pages(zone) / 100), pageblock_nr_pages);
	if (zone->nr_reserved_highatomic >= max_managed)
		return;

	spin_lock_irqsave(&zone->lock, flags);

	/* Recheck the nr_reserved_highatomic limit under the lock */
	if (zone->nr_reserved_highatomic >= max_managed)
		goto out_unlock;

	/* Yoink! */
	mt = get_pageblock_migratetype(page);
	/* Only reserve normal pageblocks (i.e., they can merge with others) */
	if (migratetype_is_mergeable(mt))
		if (move_freepages_block(zone, page, mt,
					 MIGRATE_HIGHATOMIC) != -1)
			zone->nr_reserved_highatomic += pageblock_nr_pages;

out_unlock:
	spin_unlock_irqrestore(&zone->lock, flags);
}

/*
 * Used when an allocation is about to fail under memory pressure. This
 * potentially hurts the reliability of high-order allocations when under
 * intense memory pressure but failed atomic allocations should be easier
 * to recover from than an OOM.
 *
 * If @force is true, try to unreserve a pageblock even though highatomic
 * pageblock is exhausted.
 */
static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
						bool force)
{
	struct zonelist *zonelist = ac->zonelist;
	unsigned long flags;
	struct zoneref *z;
	struct zone *zone;
	struct page *page;
	int order;
	int ret;

	for_each_zone_zonelist_nodemask(zone, z, zonelist, ac->highest_zoneidx,
								ac->nodemask) {
		/*
		 * Preserve at least one pageblock unless memory pressure
		 * is really high.
		 */
		if (!force && zone->nr_reserved_highatomic <=
					pageblock_nr_pages)
			continue;

		spin_lock_irqsave(&zone->lock, flags);
		for (order = 0; order < NR_PAGE_ORDERS; order++) {
			struct free_area *area = &(zone->free_area[order]);
			int mt;

			page = get_page_from_free_area(area, MIGRATE_HIGHATOMIC);
			if (!page)
				continue;

			mt = get_pageblock_migratetype(page);
			/*
			 * In page freeing path, migratetype change is racy so
			 * we can counter several free pages in a pageblock
			 * in this loop although we changed the pageblock type
			 * from highatomic to ac->migratetype. So we should
			 * adjust the count once.
			 */
			if (is_migrate_highatomic(mt)) {
				/*
				 * It should never happen but changes to
				 * locking could inadvertently allow a per-cpu
				 * drain to add pages to MIGRATE_HIGHATOMIC
				 * while unreserving so be safe and watch for
				 * underflows.
				 */
				zone->nr_reserved_highatomic -= min(
						pageblock_nr_pages,
						zone->nr_reserved_highatomic);
			}

			/*
			 * Convert to ac->migratetype and avoid the normal
			 * pageblock stealing heuristics. Minimally, the caller
			 * is doing the work and needs the pages. More
			 * importantly, if the block was always converted to
			 * MIGRATE_UNMOVABLE or another type then the number
			 * of pageblocks that cannot be completely freed
			 * may increase.
			 */
			ret = move_freepages_block(zone, page, mt,
						   ac->migratetype);
			/*
			 * Reserving this block already succeeded, so this should
			 * not fail on zone boundaries.
			 */
			WARN_ON_ONCE(ret == -1);
			if (ret > 0) {
				spin_unlock_irqrestore(&zone->lock, flags);
				return ret;
			}
		}
		spin_unlock_irqrestore(&zone->lock, flags);
	}

	return false;
}

/*
 * Try finding a free buddy page on the fallback list and put it on the free
 * list of requested migratetype, possibly along with other pages from the same
 * block, depending on fragmentation avoidance heuristics. Returns true if
 * fallback was found so that __rmqueue_smallest() can grab it.
 *
 * The use of signed ints for order and current_order is a deliberate
 * deviation from the rest of this file, to make the for loop
 * condition simpler.
 */
static __always_inline struct page *
__rmqueue_fallback(struct zone *zone, int order, int start_migratetype,
						unsigned int alloc_flags)
{
	struct free_area *area;
	int current_order;
	int min_order = order;
	struct page *page;
	int fallback_mt;
	bool can_steal;

	/*
	 * Do not steal pages from freelists belonging to other pageblocks
	 * i.e. orders < pageblock_order. If there are no local zones free,
	 * the zonelists will be reiterated without ALLOC_NOFRAGMENT.
	 */
	if (order < pageblock_order && alloc_flags & ALLOC_NOFRAGMENT)
		min_order = pageblock_order;

	/*
	 * Find the largest available free page in the other list. This roughly
	 * approximates finding the pageblock with the most free pages, which
	 * would be too costly to do exactly.
	 */
	for (current_order = MAX_PAGE_ORDER; current_order >= min_order;
				--current_order) {
		area = &(zone->free_area[current_order]);
		fallback_mt = find_suitable_fallback(area, current_order,
				start_migratetype, false, &can_steal);
		if (fallback_mt == -1)
			continue;

		/*
		 * We cannot steal all free pages from the pageblock and the
		 * requested migratetype is movable. In that case it's better to
		 * steal and split the smallest available page instead of the
		 * largest available page, because even if the next movable
		 * allocation falls back into a different pageblock than this
		 * one, it won't cause permanent fragmentation.
		 */
		if (!can_steal && start_migratetype == MIGRATE_MOVABLE
					&& current_order > order)
			goto find_smallest;

		goto do_steal;
	}

	return NULL;

find_smallest:
	for (current_order = order; current_order < NR_PAGE_ORDERS; current_order++) {
		area = &(zone->free_area[current_order]);
		fallback_mt = find_suitable_fallback(area, current_order,
				start_migratetype, false, &can_steal);
		if (fallback_mt != -1)
			break;
	}

	/*
	 * This should not happen - we already found a suitable fallback
	 * when looking for the largest page.
	 */
	VM_BUG_ON(current_order > MAX_PAGE_ORDER);

do_steal:
	page = get_page_from_free_area(area, fallback_mt);

	/* take off list, maybe claim block, expand remainder */
	page = steal_suitable_fallback(zone, page, current_order, order,
				       start_migratetype, alloc_flags, can_steal);

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

	return page;
}

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

	if (IS_ENABLED(CONFIG_CMA)) {
		/*
		 * Balance movable allocations between regular and CMA areas by
		 * allocating from CMA when over half of the zone's free memory
		 * is in the CMA area.
		 */
		if (alloc_flags & ALLOC_CMA &&
		    zone_page_state(zone, NR_FREE_CMA_PAGES) >
		    zone_page_state(zone, NR_FREE_PAGES) / 2) {
			page = __rmqueue_cma_fallback(zone, order);
			if (page)
				return page;
		}
	}

	page = __rmqueue_smallest(zone, order, migratetype);
	if (unlikely(!page)) {
		if (alloc_flags & ALLOC_CMA)
			page = __rmqueue_cma_fallback(zone, order);

		if (!page)
			page = __rmqueue_fallback(zone, order, migratetype,
						  alloc_flags);
	}
	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, unsigned int alloc_flags)
{
	unsigned long flags;
	int i;

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

		/*
		 * Split buddy pages returned by expand() are received here in
		 * physical page order. The page is added to the tail of
		 * caller's list. From the callers perspective, the linked list
		 * is ordered by page number under some conditions. This is
		 * useful for IO devices that can forward direction from the
		 * head, thus also in the physical page order. This is useful
		 * for IO devices that can merge IO requests if the physical
		 * pages are ordered properly.
		 */
		list_add_tail(&page->pcp_list, list);
	}
	spin_unlock_irqrestore(&zone->lock, flags);

	return i;
}

/*
 * Called from the vmstat counter updater to decay the PCP high.
 * Return whether there are addition works to do.
 */
int decay_pcp_high(struct zone *zone, struct per_cpu_pages *pcp)
{
	int high_min, to_drain, batch;
	int todo = 0;

	high_min = READ_ONCE(pcp->high_min);
	batch = READ_ONCE(pcp->batch);
	/*
	 * Decrease pcp->high periodically to try to free possible
	 * idle PCP pages.  And, avoid to free too many pages to
	 * control latency.  This caps pcp->high decrement too.
	 */
	if (pcp->high > high_min) {
		pcp->high = max3(pcp->count - (batch << CONFIG_PCP_BATCH_SCALE_MAX),
				 pcp->high - (pcp->high >> 3), high_min);
		if (pcp->high > high_min)
			todo++;
	}

	to_drain = pcp->count - pcp->high;
	if (to_drain > 0) {
		spin_lock(&pcp->lock);
		free_pcppages_bulk(zone, to_drain, pcp, 0);
		spin_unlock(&pcp->lock);
		todo++;
	}

	return todo;
}

#ifdef CONFIG_NUMA
/*
 * Called from the vmstat counter updater to drain pagesets of this
 * currently executing processor on remote nodes after they have
 * expired.
 */
void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp)
{
	int to_drain, batch;

	batch = READ_ONCE(pcp->batch);
	to_drain = min(pcp->count, batch);
	if (to_drain > 0) {
		spin_lock(&pcp->lock);
		free_pcppages_bulk(zone, to_drain, pcp, 0);
		spin_unlock(&pcp->lock);
	}
}
#endif

/*
 * Drain pcplists of the indicated processor and zone.
 */
static void drain_pages_zone(unsigned int cpu, struct zone *zone)
{
	struct per_cpu_pages *pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu);
	int count = READ_ONCE(pcp->count);

	while (count) {
		int to_drain = min(count, pcp->batch << CONFIG_PCP_BATCH_SCALE_MAX);
		count -= to_drain;

		spin_lock(&pcp->lock);
		free_pcppages_bulk(zone, to_drain, pcp, 0);
		spin_unlock(&pcp->lock);
	}
}

/*
 * Drain pcplists of all zones on the indicated processor.
 */
static void drain_pages(unsigned int cpu)
{
	struct zone *zone;

	for_each_populated_zone(zone) {
		drain_pages_zone(cpu, zone);
	}
}

/*
 * Spill all of this CPU's per-cpu pages back into the buddy allocator.
 */
void drain_local_pages(struct zone *zone)
{
	int cpu = smp_processor_id();

	if (zone)
		drain_pages_zone(cpu, zone);
	else
		drain_pages(cpu);
}

/*
 * The implementation of drain_all_pages(), exposing an extra parameter to
 * drain on all cpus.
 *
 * drain_all_pages() is optimized to only execute on cpus where pcplists are
 * not empty. The check for non-emptiness can however race with a free to
 * pcplist that has not yet increased the pcp->count from 0 to 1. Callers
 * that need the guarantee that every CPU has drained can disable the
 * optimizing racy check.
 */
static void __drain_all_pages(struct zone *zone, bool force_all_cpus)
{
	int cpu;

	/*
	 * Allocate in the BSS so we won't require allocation in
	 * direct reclaim path for CONFIG_CPUMASK_OFFSTACK=y
	 */
	static cpumask_t cpus_with_pcps;

	/*
	 * Do not drain if one is already in progress unless it's specific to
	 * a zone. Such callers are primarily CMA and memory hotplug and need
	 * the drain to be complete when the call returns.
	 */
	if (unlikely(!mutex_trylock(&pcpu_drain_mutex))) {
		if (!zone)
			return;
		mutex_lock(&pcpu_drain_mutex);
	}

	/*
	 * 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) {
		struct per_cpu_pages *pcp;
		struct zone *z;
		bool has_pcps = false;

		if (force_all_cpus) {
			/*
			 * The pcp.count check is racy, some callers need a
			 * guarantee that no cpu is missed.
			 */
			has_pcps = true;
		} else if (zone) {
			pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu);
			if (pcp->count)
				has_pcps = true;
		} else {
			for_each_populated_zone(z) {
				pcp = per_cpu_ptr(z->per_cpu_pageset, cpu);
				if (pcp->count) {
					has_pcps = true;
					break;
				}
			}
		}

		if (has_pcps)
			cpumask_set_cpu(cpu, &cpus_with_pcps);
		else
			cpumask_clear_cpu(cpu, &cpus_with_pcps);
	}

	for_each_cpu(cpu, &cpus_with_pcps) {
		if (zone)
			drain_pages_zone(cpu, zone);
		else
			drain_pages(cpu);
	}

	mutex_unlock(&pcpu_drain_mutex);
}

/*
 * Spill all the per-cpu pages from all CPUs back into the buddy allocator.
 *
 * When zone parameter is non-NULL, spill just the single zone's pages.
 */
void drain_all_pages(struct zone *zone)
{
	__drain_all_pages(zone, false);
}

static int nr_pcp_free(struct per_cpu_pages *pcp, int batch, int high, bool free_high)
{
	int min_nr_free, max_nr_free;

	/* Free as much as possible if batch freeing high-order pages. */
	if (unlikely(free_high))
		return min(pcp->count, batch << CONFIG_PCP_BATCH_SCALE_MAX);

	/* Check for PCP disabled or boot pageset */
	if (unlikely(high < batch))
		return 1;

	/* Leave at least pcp->batch pages on the list */
	min_nr_free = batch;
	max_nr_free = high - batch;

	/*
	 * Increase the batch number to the number of the consecutive
	 * freed pages to reduce zone lock contention.
	 */
	batch = clamp_t(int, pcp->free_count, min_nr_free, max_nr_free);

	return batch;
}

static int nr_pcp_high(struct per_cpu_pages *pcp, struct zone *zone,
		       int batch, bool free_high)
{
	int high, high_min, high_max;

	high_min = READ_ONCE(pcp->high_min);
	high_max = READ_ONCE(pcp->high_max);
	high = pcp->high = clamp(pcp->high, high_min, high_max);

	if (unlikely(!high))
		return 0;

	if (unlikely(free_high)) {
		pcp->high = max(high - (batch << CONFIG_PCP_BATCH_SCALE_MAX),
				high_min);
		return 0;
	}

	/*
	 * If reclaim is active, limit the number of pages that can be
	 * stored on pcp lists
	 */
	if (test_bit(ZONE_RECLAIM_ACTIVE, &zone->flags)) {
		int free_count = max_t(int, pcp->free_count, batch);

		pcp->high = max(high - free_count, high_min);
		return min(batch << 2, pcp->high);
	}

	if (high_min == high_max)
		return high;

	if (test_bit(ZONE_BELOW_HIGH, &zone->flags)) {
		int free_count = max_t(int, pcp->free_count, batch);

		pcp->high = max(high - free_count, high_min);
		high = max(pcp->count, high_min);
	} else if (pcp->count >= high) {
		int need_high = pcp->free_count + batch;

		/* pcp->high should be large enough to hold batch freed pages */
		if (pcp->high < need_high)
			pcp->high = clamp(need_high, high_min, high_max);
	}

	return high;
}

static void free_unref_page_commit(struct zone *zone, struct per_cpu_pages *pcp,
				   struct page *page, int migratetype,
				   unsigned int order)
{
	int high, batch;
	int pindex;
	bool free_high = false;

	/*
	 * On freeing, reduce the number of pages that are batch allocated.
	 * See nr_pcp_alloc() where alloc_factor is increased for subsequent
	 * allocations.
	 */
	pcp->alloc_factor >>= 1;
	__count_vm_events(PGFREE, 1 << order);
	pindex = order_to_pindex(migratetype, order);
	list_add(&page->pcp_list, &pcp->lists[pindex]);
	pcp->count += 1 << order;

	batch = READ_ONCE(pcp->batch);
	/*
	 * As high-order pages other than THP's stored on PCP can contribute
	 * to fragmentation, limit the number stored when PCP is heavily
	 * freeing without allocation. The remainder after bulk freeing
	 * stops will be drained from vmstat refresh context.
	 */
	if (order && order <= PAGE_ALLOC_COSTLY_ORDER) {
		free_high = (pcp->free_count >= batch &&
			     (pcp->flags & PCPF_PREV_FREE_HIGH_ORDER) &&
			     (!(pcp->flags & PCPF_FREE_HIGH_BATCH) ||
			      pcp->count >= READ_ONCE(batch)));
		pcp->flags |= PCPF_PREV_FREE_HIGH_ORDER;
	} else if (pcp->flags & PCPF_PREV_FREE_HIGH_ORDER) {
		pcp->flags &= ~PCPF_PREV_FREE_HIGH_ORDER;
	}
	if (pcp->free_count < (batch << CONFIG_PCP_BATCH_SCALE_MAX))
		pcp->free_count += (1 << order);
	high = nr_pcp_high(pcp, zone, batch, free_high);
	if (pcp->count >= high) {
		free_pcppages_bulk(zone, nr_pcp_free(pcp, batch, high, free_high),
				   pcp, pindex);
		if (test_bit(ZONE_BELOW_HIGH, &zone->flags) &&
		    zone_watermark_ok(zone, 0, high_wmark_pages(zone),
				      ZONE_MOVABLE, 0))
			clear_bit(ZONE_BELOW_HIGH, &zone->flags);
	}
}

/*
 * Free a pcp page
 */
void free_unref_page(struct page *page, unsigned int order)
{
	unsigned long __maybe_unused UP_flags;
	struct per_cpu_pages *pcp;
	struct zone *zone;
	unsigned long pfn = page_to_pfn(page);
	int migratetype;

	if (!pcp_allowed_order(order)) {
		__free_pages_ok(page, order, FPI_NONE);
		return;
	}

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

	/*
	 * We only track unmovable, reclaimable and movable on pcp lists.
	 * Place ISOLATE pages on the isolated list because they are being
	 * offlined but treat HIGHATOMIC and CMA as movable pages so we can
	 * get those areas back if necessary. Otherwise, we may have to free
	 * excessively into the page allocator
	 */
	migratetype = get_pfnblock_migratetype(page, pfn);
	if (unlikely(migratetype >= MIGRATE_PCPTYPES)) {
		if (unlikely(is_migrate_isolate(migratetype))) {
			free_one_page(page_zone(page), page, pfn, order, FPI_NONE);
			return;
		}
		migratetype = MIGRATE_MOVABLE;
	}

	zone = page_zone(page);
	pcp_trylock_prepare(UP_flags);
	pcp = pcp_spin_trylock(zone->per_cpu_pageset);
	if (pcp) {
		free_unref_page_commit(zone, pcp, page, migratetype, order);
		pcp_spin_unlock(pcp);
	} else {
		free_one_page(zone, page, pfn, order, FPI_NONE);
	}
	pcp_trylock_finish(UP_flags);
}

/*
 * Free a batch of folios
 */
void free_unref_folios(struct folio_batch *folios)
{
	unsigned long __maybe_unused UP_flags;
	struct per_cpu_pages *pcp = NULL;
	struct zone *locked_zone = NULL;
	int i, j;

	/* Prepare folios for freeing */
	for (i = 0, j = 0; i < folios->nr; i++) {
		struct folio *folio = folios->folios[i];
		unsigned long pfn = folio_pfn(folio);
		unsigned int order = folio_order(folio);

		if (order > 0 && folio_test_large_rmappable(folio))
			folio_undo_large_rmappable(folio);
		if (!free_pages_prepare(&folio->page, order))
			continue;
		/*
		 * Free orders not handled on the PCP directly to the
		 * allocator.
		 */
		if (!pcp_allowed_order(order)) {
			free_one_page(folio_zone(folio), &folio->page,
				      pfn, order, FPI_NONE);
			continue;
		}
		folio->private = (void *)(unsigned long)order;
		if (j != i)
			folios->folios[j] = folio;
		j++;
	}
	folios->nr = j;

	for (i = 0; i < folios->nr; i++) {
		struct folio *folio = folios->folios[i];
		struct zone *zone = folio_zone(folio);
		unsigned long pfn = folio_pfn(folio);
		unsigned int order = (unsigned long)folio->private;
		int migratetype;

		folio->private = NULL;
		migratetype = get_pfnblock_migratetype(&folio->page, pfn);

		/* Different zone requires a different pcp lock */
		if (zone != locked_zone ||
		    is_migrate_isolate(migratetype)) {
			if (pcp) {
				pcp_spin_unlock(pcp);
				pcp_trylock_finish(UP_flags);
				locked_zone = NULL;
				pcp = NULL;
			}

			/*
			 * Free isolated pages directly to the
			 * allocator, see comment in free_unref_page.
			 */
			if (is_migrate_isolate(migratetype)) {
				free_one_page(zone, &folio->page, pfn,
					      order, FPI_NONE);
				continue;
			}

			/*
			 * trylock is necessary as folios may be getting freed
			 * from IRQ or SoftIRQ context after an IO completion.
			 */
			pcp_trylock_prepare(UP_flags);
			pcp = pcp_spin_trylock(zone->per_cpu_pageset);
			if (unlikely(!pcp)) {
				pcp_trylock_finish(UP_flags);
				free_one_page(zone, &folio->page, pfn,
					      order, FPI_NONE);
				continue;
			}
			locked_zone = zone;
		}

		/*
		 * Non-isolated types over MIGRATE_PCPTYPES get added
		 * to the MIGRATE_MOVABLE pcp list.
		 */
		if (unlikely(migratetype >= MIGRATE_PCPTYPES))
			migratetype = MIGRATE_MOVABLE;

		trace_mm_page_free_batched(&folio->page);
		free_unref_page_commit(zone, pcp, &folio->page, migratetype,
				order);
	}

	if (pcp) {
		pcp_spin_unlock(pcp);
		pcp_trylock_finish(UP_flags);
	}
	folio_batch_reinit(folios);
}

/*
 * 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_PAGE(PageCompound(page), page);
	VM_BUG_ON_PAGE(!page_count(page), page);

	for (i = 1; i < (1 << order); i++)
		set_page_refcounted(page + i);
	split_page_owner(page, order, 0);
	pgalloc_tag_split(page, 1 << order);
	split_page_memcg(page, order, 0);
}
EXPORT_SYMBOL_GPL(split_page);

int __isolate_free_page(struct page *page, unsigned int order)
{
	struct zone *zone = page_zone(page);
	int mt = get_pageblock_migratetype(page);

	if (!is_migrate_isolate(mt)) {
		unsigned long watermark;
		/*
		 * Obey watermarks as if the page was being allocated. We can
		 * emulate a high-order watermark check with a raised order-0
		 * watermark, because we already know our high-order page
		 * exists.
		 */
		watermark = zone->_watermark[WMARK_MIN] + (1UL << order);
		if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
			return 0;
	}

	del_page_from_free_list(page, zone, order, mt);

	/*
	 * Set the pageblock if the isolated page is at least half of 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);
			/*
			 * Only change normal pageblocks (i.e., they can merge
			 * with others)
			 */
			if (migratetype_is_mergeable(mt))
				move_freepages_block(zone, page, mt,
						     MIGRATE_MOVABLE);
		}
	}

	return 1UL << order;
}

/**
 * __putback_isolated_page - Return a now-isolated page back where we got it
 * @page: Page that was isolated
 * @order: Order of the isolated page
 * @mt: The page's pageblock's migratetype
 *
 * This function is meant to return a page pulled from the free lists via
 * __isolate_free_page back to the free lists they were pulled from.
 */
void __putback_isolated_page(struct page *page, unsigned int order, int mt)
{
	struct zone *zone = page_zone(page);

	/* zone lock should be held when this function is called */
	lockdep_assert_held(&zone->lock);

	/* Return isolated page to tail of freelist. */
	__free_one_page(page, page_to_pfn(page), zone, order, mt,
			FPI_SKIP_REPORT_NOTIFY | FPI_TO_TAIL);
}

/*
 * Update NUMA hit/miss statistics
 */
static inline void zone_statistics(struct zone *preferred_zone, struct zone *z,
				   long nr_account)
{
#ifdef CONFIG_NUMA
	enum numa_stat_item local_stat = NUMA_LOCAL;

	/* skip numa counters update if numa stats is disabled */
	if (!static_branch_likely(&vm_numa_stat_key))
		return;

	if (zone_to_nid(z) != numa_node_id())
		local_stat = NUMA_OTHER;

	if (zone_to_nid(z) == zone_to_nid(preferred_zone))
		__count_numa_events(z, NUMA_HIT, nr_account);
	else {
		__count_numa_events(z, NUMA_MISS, nr_account);
		__count_numa_events(preferred_zone, NUMA_FOREIGN, nr_account);
	}
	__count_numa_events(z, local_stat, nr_account);
#endif
}

static __always_inline
struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
			   unsigned int order, unsigned int alloc_flags,
			   int migratetype)
{
	struct page *page;
	unsigned long flags;

	do {
		page = NULL;
		spin_lock_irqsave(&zone->lock, flags);
		if (alloc_flags & ALLOC_HIGHATOMIC)
			page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
		if (!page) {
			page = __rmqueue(zone, order, migratetype, alloc_flags);

			/*
			 * If the allocation fails, allow OOM handling access
			 * to HIGHATOMIC reserves as failing now is worse than
			 * failing a high-order atomic allocation in the
			 * future.
			 */
			if (!page && (alloc_flags & ALLOC_OOM))
				page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);

			if (!page) {
				spin_unlock_irqrestore(&zone->lock, flags);
				return NULL;
			}
		}
		spin_unlock_irqrestore(&zone->lock, flags);
	} while (check_new_pages(page, order));

	__count_zid_vm_events(PGALLOC, page_zonenum(page), 1 << order);
	zone_statistics(preferred_zone, zone, 1);

	return page;
}

static int nr_pcp_alloc(struct per_cpu_pages *pcp, struct zone *zone, int order)
{
	int high, base_batch, batch, max_nr_alloc;
	int high_max, high_min;

	base_batch = READ_ONCE(pcp->batch);
	high_min = READ_ONCE(pcp->high_min);
	high_max = READ_ONCE(pcp->high_max);
	high = pcp->high = clamp(pcp->high, high_min, high_max);

	/* Check for PCP disabled or boot pageset */
	if (unlikely(high < base_batch))
		return 1;

	if (order)
		batch = base_batch;
	else
		batch = (base_batch << pcp->alloc_factor);

	/*
	 * If we had larger pcp->high, we could avoid to allocate from
	 * zone.
	 */
	if (high_min != high_max && !test_bit(ZONE_BELOW_HIGH, &zone->flags))
		high = pcp->high = min(high + batch, high_max);

	if (!order) {
		max_nr_alloc = max(high - pcp->count - base_batch, base_batch);
		/*
		 * Double the number of pages allocated each time there is
		 * subsequent allocation of order-0 pages without any freeing.
		 */
		if (batch <= max_nr_alloc &&
		    pcp->alloc_factor < CONFIG_PCP_BATCH_SCALE_MAX)
			pcp->alloc_factor++;
		batch = min(batch, max_nr_alloc);
	}

	/*
	 * Scale batch relative to order if batch implies free pages
	 * can be stored on the PCP. Batch can be 1 for small zones or
	 * for boot pagesets which should never store free pages as
	 * the pages may belong to arbitrary zones.
	 */
	if (batch > 1)
		batch = max(batch >> order, 2);

	return batch;
}

/* Remove page from the per-cpu list, caller must protect the list */
static inline
struct page *__rmqueue_pcplist(struct zone *zone, unsigned int order,
			int migratetype,
			unsigned int alloc_flags,
			struct per_cpu_pages *pcp,
			struct list_head *list)
{
	struct page *page;

	do {
		if (list_empty(list)) {
			int batch = nr_pcp_alloc(pcp, zone, order);
			int alloced;

			alloced = rmqueue_bulk(zone, order,
					batch, list,
					migratetype, alloc_flags);

			pcp->count += alloced << order;
			if (unlikely(list_empty(list)))
				return NULL;
		}

		page = list_first_entry(list, struct page, pcp_list);
		list_del(&page->pcp_list);
		pcp->count -= 1 << order;
	} while (check_new_pages(page, order));

	return page;
}

/* Lock and remove page from the per-cpu list */
static struct page *rmqueue_pcplist(struct zone *preferred_zone,
			struct zone *zone, unsigned int order,
			int migratetype, unsigned int alloc_flags)
{
	struct per_cpu_pages *pcp;
	struct list_head *list;
	struct page *page;
	unsigned long __maybe_unused UP_flags;

	/* spin_trylock may fail due to a parallel drain or IRQ reentrancy. */
	pcp_trylock_prepare(UP_flags);
	pcp = pcp_spin_trylock(zone->per_cpu_pageset);
	if (!pcp) {
		pcp_trylock_finish(UP_flags);
		return NULL;
	}

	/*
	 * On allocation, reduce the number of pages that are batch freed.
	 * See nr_pcp_free() where free_factor is increased for subsequent
	 * frees.
	 */
	pcp->free_count >>= 1;
	list = &pcp->lists[order_to_pindex(migratetype, order)];
	page = __rmqueue_pcplist(zone, order, migratetype, alloc_flags, pcp, list);
	pcp_spin_unlock(pcp);
	pcp_trylock_finish(UP_flags);
	if (page) {
		__count_zid_vm_events(PGALLOC, page_zonenum(page), 1 << order);
		zone_statistics(preferred_zone, zone, 1);
	}
	return page;
}

/*
 * Allocate a page from the given zone.
 * Use pcplists for THP or "cheap" high-order allocations.
 */

/*
 * Do not instrument rmqueue() with KMSAN. This function may call
 * __msan_poison_alloca() through a call to set_pfnblock_flags_mask().
 * If __msan_poison_alloca() attempts to allocate pages for the stack depot, it
 * may call rmqueue() again, which will result in a deadlock.
 */
__no_sanitize_memory
static inline
struct page *rmqueue(struct zone *preferred_zone,
			struct zone *zone, unsigned int order,
			gfp_t gfp_flags, unsigned int alloc_flags,
			int migratetype)
{
	struct page *page;

	/*
	 * We most definitely don't want callers attempting to
	 * allocate greater than order-1 page units with __GFP_NOFAIL.
	 */
	WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));

	if (likely(pcp_allowed_order(order))) {
		page = rmqueue_pcplist(preferred_zone, zone, order,
				       migratetype, alloc_flags);
		if (likely(page))
			goto out;
	}

	page = rmqueue_buddy(preferred_zone, zone, order, alloc_flags,
							migratetype);

out:
	/* Separate test+clear to avoid unnecessary atomics */
	if ((alloc_flags & ALLOC_KSWAPD) &&
	    unlikely(test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags))) {
		clear_bit(ZONE_BOOSTED_WATERMARK, &zone->flags);
		wakeup_kswapd(zone, 0, 0, zone_idx(zone));
	}

	VM_BUG_ON_PAGE(page && bad_range(zone, page), page);
	return page;
}

noinline bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
{
	return __should_fail_alloc_page(gfp_mask, order);
}
ALLOW_ERROR_INJECTION(should_fail_alloc_page, TRUE);

static inline long __zone_watermark_unusable_free(struct zone *z,
				unsigned int order, unsigned int alloc_flags)
{
	long unusable_free = (1 << order) - 1;

	/*
	 * If the caller does not have rights to reserves below the min
	 * watermark then subtract the high-atomic reserves. This will
	 * over-estimate the size of the atomic reserve but it avoids a search.
	 */
	if (likely(!(alloc_flags & ALLOC_RESERVES)))
		unusable_free += z->nr_reserved_highatomic;

#ifdef CONFIG_CMA
	/* If allocation can't use CMA areas don't use free CMA pages */
	if (!(alloc_flags & ALLOC_CMA))
		unusable_free += zone_page_state(z, NR_FREE_CMA_PAGES);
#endif
#ifdef CONFIG_UNACCEPTED_MEMORY
	unusable_free += zone_page_state(z, NR_UNACCEPTED);
#endif

	return unusable_free;
}

/*
 * Return true if free base pages are above 'mark'. For high-order checks it
 * will return true of the order-0 watermark is reached and there is at least
 * one free page of a suitable size. Checking now avoids taking the zone lock
 * to check in the allocation paths if no pages are free.
 */
bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
			 int highest_zoneidx, unsigned int alloc_flags,
			 long free_pages)
{
	long min = mark;
	int o;

	/* free_pages may go negative - that's OK */
	free_pages -= __zone_watermark_unusable_free(z, order, alloc_flags);

	if (unlikely(alloc_flags & ALLOC_RESERVES)) {
		/*
		 * __GFP_HIGH allows access to 50% of the min reserve as well
		 * as OOM.
		 */
		if (alloc_flags & ALLOC_MIN_RESERVE) {
			min -= min / 2;

			/*
			 * Non-blocking allocations (e.g. GFP_ATOMIC) can
			 * access more reserves than just __GFP_HIGH. Other
			 * non-blocking allocations requests such as GFP_NOWAIT
			 * or (GFP_KERNEL & ~__GFP_DIRECT_RECLAIM) do not get
			 * access to the min reserve.
			 */
			if (alloc_flags & ALLOC_NON_BLOCK)
				min -= min / 4;
		}

		/*
		 * OOM victims can try even harder than the normal reserve
		 * users on the grounds that it's definitely going to be in
		 * the exit path shortly and free memory. Any allocation it
		 * makes during the free path will be small and short-lived.
		 */
		if (alloc_flags & ALLOC_OOM)
			min -= min / 2;
	}

	/*
	 * Check watermarks for an order-0 allocation request. If these
	 * are not met, then a high-order request also cannot go ahead
	 * even if a suitable page happened to be free.
	 */
	if (free_pages <= min + z->lowmem_reserve[highest_zoneidx])
		return false;

	/* If this is an order-0 request then the watermark is fine */
	if (!order)
		return true;

	/* For a high-order request, check at least one suitable page is free */
	for (o = order; o < NR_PAGE_ORDERS; o++) {
		struct free_area *area = &z->free_area[o];
		int mt;

		if (!area->nr_free)
			continue;

		for (mt = 0; mt < MIGRATE_PCPTYPES; mt++) {
			if (!free_area_empty(area, mt))
				return true;
		}

#ifdef CONFIG_CMA
		if ((alloc_flags & ALLOC_CMA) &&
		    !free_area_empty(area, MIGRATE_CMA)) {
			return true;
		}
#endif
		if ((alloc_flags & (ALLOC_HIGHATOMIC|ALLOC_OOM)) &&
		    !free_area_empty(area, MIGRATE_HIGHATOMIC)) {
			return true;
		}
	}
	return false;
}

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

static inline bool zone_watermark_fast(struct zone *z, unsigned int order,
				unsigned long mark, int highest_zoneidx,
				unsigned int alloc_flags, gfp_t gfp_mask)
{
	long free_pages;

	free_pages = zone_page_state(z, NR_FREE_PAGES);

	/*
	 * Fast check for order-0 only. If this fails then the reserves
	 * need to be calculated.
	 */
	if (!order) {
		long usable_free;
		long reserved;

		usable_free = free_pages;
		reserved = __zone_watermark_unusable_free(z, 0, alloc_flags);

		/* reserved may over estimate high-atomic reserves. */
		usable_free -= min(usable_free, reserved);
		if (usable_free > mark + z->lowmem_reserve[highest_zoneidx])
			return true;
	}

	if (__zone_watermark_ok(z, order, mark, highest_zoneidx, alloc_flags,
					free_pages))
		return true;

	/*
	 * Ignore watermark boosting for __GFP_HIGH order-0 allocations
	 * when checking the min watermark. The min watermark is the
	 * point where boosting is ignored so that kswapd is woken up
	 * when below the low watermark.
	 */
	if (unlikely(!order && (alloc_flags & ALLOC_MIN_RESERVE) && z->watermark_boost
		&& ((alloc_flags & ALLOC_WMARK_MASK) == WMARK_MIN))) {
		mark = z->_watermark[WMARK_MIN];
		return __zone_watermark_ok(z, order, mark, highest_zoneidx,
					alloc_flags, free_pages);
	}

	return false;
}

bool zone_watermark_ok_safe(struct zone *z, unsigned int order,
			unsigned long mark, int highest_zoneidx)
{
	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, highest_zoneidx, 0,
								free_pages);
}

#ifdef CONFIG_NUMA
int __read_mostly node_reclaim_distance = RECLAIM_DISTANCE;

static bool zone_allows_reclaim(struct zone *local_zone, struct zone *zone)
{
	return node_distance(zone_to_nid(local_zone), zone_to_nid(zone)) <=
				node_reclaim_distance;
}
#else	/* CONFIG_NUMA */
static bool zone_allows_reclaim(struct zone *local_zone, struct zone *zone)
{
	return true;
}
#endif	/* CONFIG_NUMA */

/*
 * The restriction on ZONE_DMA32 as being a suitable zone to use to avoid
 * fragmentation is subtle. If the preferred zone was HIGHMEM then
 * premature use of a lower zone may cause lowmem pressure problems that
 * are worse than fragmentation. If the next zone is ZONE_DMA then it is
 * probably too small. It only makes sense to spread allocations to avoid
 * fragmentation between the Normal and DMA32 zones.
 */
static inline unsigned int
alloc_flags_nofragment(struct zone *zone, gfp_t gfp_mask)
{
	unsigned int alloc_flags;

	/*
	 * __GFP_KSWAPD_RECLAIM is assumed to be the same as ALLOC_KSWAPD
	 * to save a branch.
	 */
	alloc_flags = (__force int) (gfp_mask & __GFP_KSWAPD_RECLAIM);

#ifdef CONFIG_ZONE_DMA32
	if (!zone)
		return alloc_flags;