kernel / mm / page_owner.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/debugfs.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/memblock.h>
#include <linux/stacktrace.h>
#include <linux/page_owner.h>
#include <linux/jump_label.h>
#include <linux/migrate.h>
#include <linux/stackdepot.h>
#include <linux/seq_file.h>
#include <linux/memcontrol.h>
#include <linux/sched/clock.h>

#include "internal.h"

/*
 * TODO: teach PAGE_OWNER_STACK_DEPTH (__dump_page_owner and save_stack)
 * to use off stack temporal storage
 */
#define PAGE_OWNER_STACK_DEPTH (16)

struct page_owner {
	unsigned short order;
	short last_migrate_reason;
	gfp_t gfp_mask;
	depot_stack_handle_t handle;
	depot_stack_handle_t free_handle;
	u64 ts_nsec;
	u64 free_ts_nsec;
	char comm[TASK_COMM_LEN];
	pid_t pid;
	pid_t tgid;
	pid_t free_pid;
	pid_t free_tgid;
};

struct stack {
	struct stack_record *stack_record;
	struct stack *next;
};
static struct stack dummy_stack;
static struct stack failure_stack;
static struct stack *stack_list;
static DEFINE_SPINLOCK(stack_list_lock);

#define STACK_PRINT_FLAG_STACK		0x1
#define STACK_PRINT_FLAG_PAGES		0x2
#define STACK_PRINT_FLAG_HANDLE		0x4

struct stack_print_ctx {
	struct stack *stack;
	u8 flags;
};

static bool page_owner_enabled __initdata;
DEFINE_STATIC_KEY_FALSE(page_owner_inited);

static depot_stack_handle_t dummy_handle;
static depot_stack_handle_t failure_handle;
static depot_stack_handle_t early_handle;

static void init_early_allocated_pages(void);

static inline void set_current_in_page_owner(void)
{
	/*
	 * Avoid recursion.
	 *
	 * We might need to allocate more memory from page_owner code, so make
	 * sure to signal it in order to avoid recursion.
	 */
	current->in_page_owner = 1;
}

static inline void unset_current_in_page_owner(void)
{
	current->in_page_owner = 0;
}

static int __init early_page_owner_param(char *buf)
{
	int ret = kstrtobool(buf, &page_owner_enabled);

	if (page_owner_enabled)
		stack_depot_request_early_init();

	return ret;
}
early_param("page_owner", early_page_owner_param);

static __init bool need_page_owner(void)
{
	return page_owner_enabled;
}

static __always_inline depot_stack_handle_t create_dummy_stack(void)
{
	unsigned long entries[4];
	unsigned int nr_entries;

	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
	return stack_depot_save(entries, nr_entries, GFP_KERNEL);
}

static noinline void register_dummy_stack(void)
{
	dummy_handle = create_dummy_stack();
}

static noinline void register_failure_stack(void)
{
	failure_handle = create_dummy_stack();
}

static noinline void register_early_stack(void)
{
	early_handle = create_dummy_stack();
}

static __init void init_page_owner(void)
{
	if (!page_owner_enabled)
		return;

	register_dummy_stack();
	register_failure_stack();
	register_early_stack();
	init_early_allocated_pages();
	/* Initialize dummy and failure stacks and link them to stack_list */
	dummy_stack.stack_record = __stack_depot_get_stack_record(dummy_handle);
	failure_stack.stack_record = __stack_depot_get_stack_record(failure_handle);
	if (dummy_stack.stack_record)
		refcount_set(&dummy_stack.stack_record->count, 1);
	if (failure_stack.stack_record)
		refcount_set(&failure_stack.stack_record->count, 1);
	dummy_stack.next = &failure_stack;
	stack_list = &dummy_stack;
	static_branch_enable(&page_owner_inited);
}

struct page_ext_operations page_owner_ops = {
	.size = sizeof(struct page_owner),
	.need = need_page_owner,
	.init = init_page_owner,
	.need_shared_flags = true,
};

static inline struct page_owner *get_page_owner(struct page_ext *page_ext)
{
	return page_ext_data(page_ext, &page_owner_ops);
}

static noinline depot_stack_handle_t save_stack(gfp_t flags)
{
	unsigned long entries[PAGE_OWNER_STACK_DEPTH];
	depot_stack_handle_t handle;
	unsigned int nr_entries;

	if (current->in_page_owner)
		return dummy_handle;

	set_current_in_page_owner();
	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
	handle = stack_depot_save(entries, nr_entries, flags);
	if (!handle)
		handle = failure_handle;
	unset_current_in_page_owner();

	return handle;
}

static void add_stack_record_to_list(struct stack_record *stack_record,
				     gfp_t gfp_mask)
{
	unsigned long flags;
	struct stack *stack;

	if (!gfpflags_allow_spinning(gfp_mask))
		return;

	set_current_in_page_owner();
	stack = kmalloc(sizeof(*stack), gfp_nested_mask(gfp_mask));
	if (!stack) {
		unset_current_in_page_owner();
		return;
	}
	unset_current_in_page_owner();

	stack->stack_record = stack_record;
	stack->next = NULL;

	spin_lock_irqsave(&stack_list_lock, flags);
	stack->next = stack_list;
	/*
	 * This pairs with smp_load_acquire() from function
	 * stack_start(). This guarantees that stack_start()
	 * will see an updated stack_list before starting to
	 * traverse the list.
	 */
	smp_store_release(&stack_list, stack);
	spin_unlock_irqrestore(&stack_list_lock, flags);
}

static void inc_stack_record_count(depot_stack_handle_t handle, gfp_t gfp_mask,
				   int nr_base_pages)
{
	struct stack_record *stack_record = __stack_depot_get_stack_record(handle);

	if (!stack_record)
		return;

	/*
	 * New stack_record's that do not use STACK_DEPOT_FLAG_GET start
	 * with REFCOUNT_SATURATED to catch spurious increments of their
	 * refcount.
	 * Since we do not use STACK_DEPOT_FLAG_GET API, let us
	 * set a refcount of 1 ourselves.
	 */
	if (refcount_read(&stack_record->count) == REFCOUNT_SATURATED) {
		int old = REFCOUNT_SATURATED;

		if (atomic_try_cmpxchg_relaxed(&stack_record->count.refs, &old, 1))
			/* Add the new stack_record to our list */
			add_stack_record_to_list(stack_record, gfp_mask);
	}
	refcount_add(nr_base_pages, &stack_record->count);
}

static void dec_stack_record_count(depot_stack_handle_t handle,
				   int nr_base_pages)
{
	struct stack_record *stack_record = __stack_depot_get_stack_record(handle);

	if (!stack_record)
		return;

	if (refcount_sub_and_test(nr_base_pages, &stack_record->count))
		pr_warn("%s: refcount went to 0 for %u handle\n", __func__,
			handle);
}

static inline void __update_page_owner_handle(struct page *page,
					      depot_stack_handle_t handle,
					      unsigned short order,
					      gfp_t gfp_mask,
					      short last_migrate_reason, u64 ts_nsec,
					      pid_t pid, pid_t tgid, char *comm)
{
	struct page_ext_iter iter;
	struct page_ext *page_ext;
	struct page_owner *page_owner;

	rcu_read_lock();
	for_each_page_ext(page, 1 << order, page_ext, iter) {
		page_owner = get_page_owner(page_ext);
		page_owner->handle = handle;
		page_owner->order = order;
		page_owner->gfp_mask = gfp_mask;
		page_owner->last_migrate_reason = last_migrate_reason;
		page_owner->pid = pid;
		page_owner->tgid = tgid;
		page_owner->ts_nsec = ts_nsec;
		strscpy(page_owner->comm, comm,
			sizeof(page_owner->comm));
		__set_bit(PAGE_EXT_OWNER, &page_ext->flags);
		__set_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
	}
	rcu_read_unlock();
}

static inline void __update_page_owner_free_handle(struct page *page,
						   depot_stack_handle_t handle,
						   unsigned short order,
						   pid_t pid, pid_t tgid,
						   u64 free_ts_nsec)
{
	struct page_ext_iter iter;
	struct page_ext *page_ext;
	struct page_owner *page_owner;

	rcu_read_lock();
	for_each_page_ext(page, 1 << order, page_ext, iter) {
		page_owner = get_page_owner(page_ext);
		/* Only __reset_page_owner() wants to clear the bit */
		if (handle) {
			__clear_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
			page_owner->free_handle = handle;
		}
		page_owner->free_ts_nsec = free_ts_nsec;
		page_owner->free_pid = current->pid;
		page_owner->free_tgid = current->tgid;
	}
	rcu_read_unlock();
}

void __reset_page_owner(struct page *page, unsigned short order)
{
	struct page_ext *page_ext;
	depot_stack_handle_t handle;
	depot_stack_handle_t alloc_handle;
	struct page_owner *page_owner;
	u64 free_ts_nsec = local_clock();

	page_ext = page_ext_get(page);
	if (unlikely(!page_ext))
		return;

	page_owner = get_page_owner(page_ext);
	alloc_handle = page_owner->handle;
	page_ext_put(page_ext);

	/*
	 * Do not specify GFP_NOWAIT to make gfpflags_allow_spinning() == false
	 * to prevent issues in stack_depot_save().
	 * This is similar to alloc_pages_nolock() gfp flags, but only used
	 * to signal stack_depot to avoid spin_locks.
	 */
	handle = save_stack(__GFP_NOWARN);
	__update_page_owner_free_handle(page, handle, order, current->pid,
					current->tgid, free_ts_nsec);

	if (alloc_handle != early_handle)
		/*
		 * early_handle is being set as a handle for all those
		 * early allocated pages. See init_pages_in_zone().
		 * Since their refcount is not being incremented because
		 * the machinery is not ready yet, we cannot decrement
		 * their refcount either.
		 */
		dec_stack_record_count(alloc_handle, 1 << order);
}

noinline void __set_page_owner(struct page *page, unsigned short order,
					gfp_t gfp_mask)
{
	u64 ts_nsec = local_clock();
	depot_stack_handle_t handle;

	handle = save_stack(gfp_mask);
	__update_page_owner_handle(page, handle, order, gfp_mask, -1,
				   ts_nsec, current->pid, current->tgid,
				   current->comm);
	inc_stack_record_count(handle, gfp_mask, 1 << order);
}

void __folio_set_owner_migrate_reason(struct folio *folio, int reason)
{
	struct page_ext *page_ext = page_ext_get(&folio->page);
	struct page_owner *page_owner;

	if (unlikely(!page_ext))
		return;

	page_owner = get_page_owner(page_ext);
	page_owner->last_migrate_reason = reason;
	page_ext_put(page_ext);
}

void __split_page_owner(struct page *page, int old_order, int new_order)
{
	struct page_ext_iter iter;
	struct page_ext *page_ext;
	struct page_owner *page_owner;

	rcu_read_lock();
	for_each_page_ext(page, 1 << old_order, page_ext, iter) {
		page_owner = get_page_owner(page_ext);
		page_owner->order = new_order;
	}
	rcu_read_unlock();
}

void __folio_copy_owner(struct folio *newfolio, struct folio *old)
{
	struct page_ext *page_ext;
	struct page_ext_iter iter;
	struct page_owner *old_page_owner;
	struct page_owner *new_page_owner;
	depot_stack_handle_t migrate_handle;

	page_ext = page_ext_get(&old->page);
	if (unlikely(!page_ext))
		return;

	old_page_owner = get_page_owner(page_ext);
	page_ext_put(page_ext);

	page_ext = page_ext_get(&newfolio->page);
	if (unlikely(!page_ext))
		return;

	new_page_owner = get_page_owner(page_ext);
	page_ext_put(page_ext);

	migrate_handle = new_page_owner->handle;
	__update_page_owner_handle(&newfolio->page, old_page_owner->handle,
				   old_page_owner->order, old_page_owner->gfp_mask,
				   old_page_owner->last_migrate_reason,
				   old_page_owner->ts_nsec, old_page_owner->pid,
				   old_page_owner->tgid, old_page_owner->comm);
	/*
	 * Do not proactively clear PAGE_EXT_OWNER{_ALLOCATED} bits as the folio
	 * will be freed after migration. Keep them until then as they may be
	 * useful.
	 */
	__update_page_owner_free_handle(&newfolio->page, 0, old_page_owner->order,
					old_page_owner->free_pid,
					old_page_owner->free_tgid,
					old_page_owner->free_ts_nsec);
	/*
	 * We linked the original stack to the new folio, we need to do the same
	 * for the new one and the old folio otherwise there will be an imbalance
	 * when subtracting those pages from the stack.
	 */
	rcu_read_lock();
	for_each_page_ext(&old->page, 1 << new_page_owner->order, page_ext, iter) {
		old_page_owner = get_page_owner(page_ext);
		old_page_owner->handle = migrate_handle;
	}
	rcu_read_unlock();
}

void pagetypeinfo_showmixedcount_print(struct seq_file *m,
				       pg_data_t *pgdat, struct zone *zone)
{
	struct page *page;
	struct page_ext *page_ext;
	struct page_owner *page_owner;
	unsigned long pfn, block_end_pfn;
	unsigned long end_pfn = zone_end_pfn(zone);
	unsigned long count[MIGRATE_TYPES] = { 0, };
	int pageblock_mt, page_mt;
	int i;

	/* Scan block by block. First and last block may be incomplete */
	pfn = zone->zone_start_pfn;

	/*
	 * Walk the zone in pageblock_nr_pages steps. If a page block spans
	 * a zone boundary, it will be double counted between zones. This does
	 * not matter as the mixed block count will still be correct
	 */
	for (; pfn < end_pfn; ) {
		page = pfn_to_online_page(pfn);
		if (!page) {
			pfn = ALIGN(pfn + 1, MAX_ORDER_NR_PAGES);
			continue;
		}

		block_end_pfn = pageblock_end_pfn(pfn);
		block_end_pfn = min(block_end_pfn, end_pfn);

		pageblock_mt = get_pageblock_migratetype(page);

		for (; pfn < block_end_pfn; pfn++) {
			/* The pageblock is online, no need to recheck. */
			page = pfn_to_page(pfn);

			if (page_zone(page) != zone)
				continue;

			if (PageBuddy(page)) {
				unsigned long freepage_order;

				freepage_order = buddy_order_unsafe(page);
				if (freepage_order <= MAX_PAGE_ORDER)
					pfn += (1UL << freepage_order) - 1;
				continue;
			}

			if (PageReserved(page))
				continue;

			page_ext = page_ext_get(page);
			if (unlikely(!page_ext))
				continue;

			if (!test_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags))
				goto ext_put_continue;

			page_owner = get_page_owner(page_ext);
			page_mt = gfp_migratetype(page_owner->gfp_mask);
			if (pageblock_mt != page_mt) {
				if (is_migrate_cma(pageblock_mt))
					count[MIGRATE_MOVABLE]++;
				else
					count[pageblock_mt]++;

				pfn = block_end_pfn;
				page_ext_put(page_ext);
				break;
			}
			pfn += (1UL << page_owner->order) - 1;
ext_put_continue:
			page_ext_put(page_ext);
		}
	}

	/* Print counts */
	seq_printf(m, "Node %d, zone %8s ", pgdat->node_id, zone->name);
	for (i = 0; i < MIGRATE_TYPES; i++)
		seq_printf(m, "%12lu ", count[i]);
	seq_putc(m, '\n');
}

/*
 * Looking for memcg information and print it out
 */
static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret,
					 struct page *page)
{
#ifdef CONFIG_MEMCG
	unsigned long memcg_data;
	struct mem_cgroup *memcg;
	bool online;
	char name[80];

	rcu_read_lock();
	memcg_data = READ_ONCE(page->memcg_data);
	if (!memcg_data || PageTail(page))
		goto out_unlock;

	if (memcg_data & MEMCG_DATA_OBJEXTS)
		ret += scnprintf(kbuf + ret, count - ret,
				"Slab cache page\n");

	memcg = page_memcg_check(page);
	if (!memcg)
		goto out_unlock;

	online = (memcg->css.flags & CSS_ONLINE);
	cgroup_name(memcg->css.cgroup, name, sizeof(name));
	ret += scnprintf(kbuf + ret, count - ret,
			"Charged %sto %smemcg %s\n",
			PageMemcgKmem(page) ? "(via objcg) " : "",
			online ? "" : "offline ",
			name);
out_unlock:
	rcu_read_unlock();
#endif /* CONFIG_MEMCG */

	return ret;
}

static ssize_t
print_page_owner(char __user *buf, size_t count, unsigned long pfn,
		struct page *page, struct page_owner *page_owner,
		depot_stack_handle_t handle)
{
	int ret, pageblock_mt, page_mt;
	char *kbuf;

	count = min_t(size_t, count, PAGE_SIZE);
	kbuf = kmalloc(count, GFP_KERNEL);
	if (!kbuf)
		return -ENOMEM;

	ret = scnprintf(kbuf, count,
			"Page allocated via order %u, mask %#x(%pGg), pid %d, tgid %d (%s), ts %llu ns\n",
			page_owner->order, page_owner->gfp_mask,
			&page_owner->gfp_mask, page_owner->pid,
			page_owner->tgid, page_owner->comm,
			page_owner->ts_nsec);

	/* Print information relevant to grouping pages by mobility */
	pageblock_mt = get_pageblock_migratetype(page);
	page_mt  = gfp_migratetype(page_owner->gfp_mask);
	ret += scnprintf(kbuf + ret, count - ret,
			"PFN 0x%lx type %s Block %lu type %s Flags %pGp\n",
			pfn,
			migratetype_names[page_mt],
			pfn >> pageblock_order,
			migratetype_names[pageblock_mt],
			&page->flags);

	ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
	if (ret >= count)
		goto err;

	if (page_owner->last_migrate_reason != -1) {
		ret += scnprintf(kbuf + ret, count - ret,
			"Page has been migrated, last migrate reason: %s\n",
			migrate_reason_names[page_owner->last_migrate_reason]);
	}

	ret = print_page_owner_memcg(kbuf, count, ret, page);

	ret += snprintf(kbuf + ret, count - ret, "\n");
	if (ret >= count)
		goto err;

	if (copy_to_user(buf, kbuf, ret))
		ret = -EFAULT;

	kfree(kbuf);
	return ret;

err:
	kfree(kbuf);
	return -ENOMEM;
}

void __dump_page_owner(const struct page *page)
{
	struct page_ext *page_ext = page_ext_get((void *)page);
	struct page_owner *page_owner;
	depot_stack_handle_t handle;
	gfp_t gfp_mask;
	int mt;

	if (unlikely(!page_ext)) {
		pr_alert("There is not page extension available.\n");
		return;
	}

	page_owner = get_page_owner(page_ext);
	gfp_mask = page_owner->gfp_mask;
	mt = gfp_migratetype(gfp_mask);

	if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) {
		pr_alert("page_owner info is not present (never set?)\n");
		page_ext_put(page_ext);
		return;
	}

	if (test_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags))
		pr_alert("page_owner tracks the page as allocated\n");
	else
		pr_alert("page_owner tracks the page as freed\n");

	pr_alert("page last allocated via order %u, migratetype %s, gfp_mask %#x(%pGg), pid %d, tgid %d (%s), ts %llu, free_ts %llu\n",
		 page_owner->order, migratetype_names[mt], gfp_mask, &gfp_mask,
		 page_owner->pid, page_owner->tgid, page_owner->comm,
		 page_owner->ts_nsec, page_owner->free_ts_nsec);

	handle = READ_ONCE(page_owner->handle);
	if (!handle)
		pr_alert("page_owner allocation stack trace missing\n");
	else
		stack_depot_print(handle);

	handle = READ_ONCE(page_owner->free_handle);
	if (!handle) {
		pr_alert("page_owner free stack trace missing\n");
	} else {
		pr_alert("page last free pid %d tgid %d stack trace:\n",
			  page_owner->free_pid, page_owner->free_tgid);
		stack_depot_print(handle);
	}

	if (page_owner->last_migrate_reason != -1)
		pr_alert("page has been migrated, last migrate reason: %s\n",
			migrate_reason_names[page_owner->last_migrate_reason]);
	page_ext_put(page_ext);
}

static ssize_t
read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
	unsigned long pfn;
	struct page *page;
	struct page_ext *page_ext;
	struct page_owner *page_owner;
	depot_stack_handle_t handle;

	if (!static_branch_unlikely(&page_owner_inited))
		return -EINVAL;

	page = NULL;
	if (*ppos == 0)
		pfn = min_low_pfn;
	else
		pfn = *ppos;
	/* Find a valid PFN or the start of a MAX_ORDER_NR_PAGES area */
	while (!pfn_valid(pfn) && (pfn & (MAX_ORDER_NR_PAGES - 1)) != 0)
		pfn++;

	/* Find an allocated page */
	for (; pfn < max_pfn; pfn++) {
		/*
		 * This temporary page_owner is required so
		 * that we can avoid the context switches while holding
		 * the rcu lock and copying the page owner information to
		 * user through copy_to_user() or GFP_KERNEL allocations.
		 */
		struct page_owner page_owner_tmp;

		/*
		 * If the new page is in a new MAX_ORDER_NR_PAGES area,
		 * validate the area as existing, skip it if not
		 */
		if ((pfn & (MAX_ORDER_NR_PAGES - 1)) == 0 && !pfn_valid(pfn)) {
			pfn += MAX_ORDER_NR_PAGES - 1;
			continue;
		}

		page = pfn_to_page(pfn);
		if (PageBuddy(page)) {
			unsigned long freepage_order = buddy_order_unsafe(page);

			if (freepage_order <= MAX_PAGE_ORDER)
				pfn += (1UL << freepage_order) - 1;
			continue;
		}

		page_ext = page_ext_get(page);
		if (unlikely(!page_ext))
			continue;

		/*
		 * Some pages could be missed by concurrent allocation or free,
		 * because we don't hold the zone lock.
		 */
		if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags))
			goto ext_put_continue;

		/*
		 * Although we do have the info about past allocation of free
		 * pages, it's not relevant for current memory usage.
		 */
		if (!test_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags))
			goto ext_put_continue;

		page_owner = get_page_owner(page_ext);

		/*
		 * Don't print "tail" pages of high-order allocations as that
		 * would inflate the stats.
		 */
		if (!IS_ALIGNED(pfn, 1 << page_owner->order))
			goto ext_put_continue;

		/*
		 * Access to page_ext->handle isn't synchronous so we should
		 * be careful to access it.
		 */
		handle = READ_ONCE(page_owner->handle);
		if (!handle)
			goto ext_put_continue;

		/* Record the next PFN to read in the file offset */
		*ppos = pfn + 1;

		page_owner_tmp = *page_owner;
		page_ext_put(page_ext);
		return print_page_owner(buf, count, pfn, page,
				&page_owner_tmp, handle);
ext_put_continue:
		page_ext_put(page_ext);
	}

	return 0;
}

static loff_t lseek_page_owner(struct file *file, loff_t offset, int orig)
{
	switch (orig) {
	case SEEK_SET:
		file->f_pos = offset;
		break;
	case SEEK_CUR:
		file->f_pos += offset;
		break;
	default:
		return -EINVAL;
	}
	return file->f_pos;
}

static void init_pages_in_zone(struct zone *zone)
{
	unsigned long pfn = zone->zone_start_pfn;
	unsigned long end_pfn = zone_end_pfn(zone);
	unsigned long count = 0;

	/*
	 * Walk the zone in pageblock_nr_pages steps. If a page block spans
	 * a zone boundary, it will be double counted between zones. This does
	 * not matter as the mixed block count will still be correct
	 */
	for (; pfn < end_pfn; ) {
		unsigned long block_end_pfn;

		if (!pfn_valid(pfn)) {
			pfn = ALIGN(pfn + 1, MAX_ORDER_NR_PAGES);
			continue;
		}

		block_end_pfn = pageblock_end_pfn(pfn);
		block_end_pfn = min(block_end_pfn, end_pfn);

		for (; pfn < block_end_pfn; pfn++) {
			struct page *page = pfn_to_page(pfn);
			struct page_ext *page_ext;

			if (page_zone(page) != zone)
				continue;

			/*
			 * To avoid having to grab zone->lock, be a little
			 * careful when reading buddy page order. The only
			 * danger is that we skip too much and potentially miss
			 * some early allocated pages, which is better than
			 * heavy lock contention.
			 */
			if (PageBuddy(page)) {
				unsigned long order = buddy_order_unsafe(page);

				if (order > 0 && order <= MAX_PAGE_ORDER)
					pfn += (1UL << order) - 1;
				continue;
			}

			if (PageReserved(page))
				continue;

			page_ext = page_ext_get(page);
			if (unlikely(!page_ext))
				continue;

			/* Maybe overlapping zone */
			if (test_bit(PAGE_EXT_OWNER, &page_ext->flags))
				goto ext_put_continue;

			/* Found early allocated page */
			__update_page_owner_handle(page, early_handle, 0, 0,
						   -1, local_clock(), current->pid,
						   current->tgid, current->comm);
			count++;
ext_put_continue:
			page_ext_put(page_ext);
		}
		cond_resched();
	}

	pr_info("Node %d, zone %8s: page owner found early allocated %lu pages\n",
		zone->zone_pgdat->node_id, zone->name, count);
}

static void init_early_allocated_pages(void)
{
	struct zone *zone;

	for_each_populated_zone(zone)
		init_pages_in_zone(zone);
}

static const struct file_operations page_owner_fops = {
	.read		= read_page_owner,
	.llseek		= lseek_page_owner,
};

static void *stack_start(struct seq_file *m, loff_t *ppos)
{
	struct stack *stack;
	struct stack_print_ctx *ctx = m->private;

	if (*ppos == -1UL)
		return NULL;

	if (!*ppos) {
		/*
		 * This pairs with smp_store_release() from function
		 * add_stack_record_to_list(), so we get a consistent
		 * value of stack_list.
		 */
		stack = smp_load_acquire(&stack_list);
		ctx->stack = stack;
	} else {
		stack = ctx->stack;
	}

	return stack;
}

static void *stack_next(struct seq_file *m, void *v, loff_t *ppos)
{
	struct stack *stack = v;
	struct stack_print_ctx *ctx = m->private;

	stack = stack->next;
	*ppos = stack ? *ppos + 1 : -1UL;
	ctx->stack = stack;

	return stack;
}

static unsigned long page_owner_pages_threshold;

static int stack_print(struct seq_file *m, void *v)
{
	int i, nr_base_pages;
	struct stack *stack = v;
	unsigned long *entries;
	unsigned long nr_entries;
	struct stack_record *stack_record = stack->stack_record;
	struct stack_print_ctx *ctx = m->private;

	if (!stack->stack_record)
		return 0;

	nr_base_pages = refcount_read(&stack_record->count) - 1;

	if (ctx->flags & STACK_PRINT_FLAG_PAGES &&
	    (nr_base_pages < 1 || nr_base_pages < page_owner_pages_threshold))
		return 0;

	if (ctx->flags & STACK_PRINT_FLAG_STACK) {
		nr_entries = stack_record->size;
		entries = stack_record->entries;
		for (i = 0; i < nr_entries; i++)
			seq_printf(m, " %pS\n", (void *)entries[i]);
	}
	if (ctx->flags & STACK_PRINT_FLAG_HANDLE)
		seq_printf(m, "handle: %d\n", stack_record->handle.handle);
	if (ctx->flags & STACK_PRINT_FLAG_PAGES)
		seq_printf(m, "nr_base_pages: %d\n", nr_base_pages);
	seq_putc(m, '\n');

	return 0;
}

static void stack_stop(struct seq_file *m, void *v)
{
}

static const struct seq_operations page_owner_stack_op = {
	.start	= stack_start,
	.next	= stack_next,
	.stop	= stack_stop,
	.show	= stack_print
};

static int page_owner_stack_open(struct inode *inode, struct file *file)
{
	int ret = seq_open_private(file, &page_owner_stack_op,
				   sizeof(struct stack_print_ctx));

	if (!ret) {
		struct seq_file *m = file->private_data;
		struct stack_print_ctx *ctx = m->private;

		ctx->flags = (uintptr_t) inode->i_private;
	}

	return ret;
}

static const struct file_operations page_owner_stack_fops = {
	.open		= page_owner_stack_open,
	.read		= seq_read,
	.llseek		= seq_lseek,
	.release	= seq_release_private,
};

static int page_owner_threshold_get(void *data, u64 *val)
{
	*val = READ_ONCE(page_owner_pages_threshold);
	return 0;
}

static int page_owner_threshold_set(void *data, u64 val)
{
	WRITE_ONCE(page_owner_pages_threshold, val);
	return 0;
}

DEFINE_SIMPLE_ATTRIBUTE(page_owner_threshold_fops, &page_owner_threshold_get,
			&page_owner_threshold_set, "%llu");


static int __init pageowner_init(void)
{
	struct dentry *dir;

	if (!static_branch_unlikely(&page_owner_inited)) {
		pr_info("page_owner is disabled\n");
		return 0;
	}

	debugfs_create_file("page_owner", 0400, NULL, NULL, &page_owner_fops);
	dir = debugfs_create_dir("page_owner_stacks", NULL);
	debugfs_create_file("show_stacks", 0400, dir,
			    (void *)(STACK_PRINT_FLAG_STACK |
				     STACK_PRINT_FLAG_PAGES),
			     &page_owner_stack_fops);
	debugfs_create_file("show_handles", 0400, dir,
			    (void *)(STACK_PRINT_FLAG_HANDLE |
				     STACK_PRINT_FLAG_PAGES),
			    &page_owner_stack_fops);
	debugfs_create_file("show_stacks_handles", 0400, dir,
			    (void *)(STACK_PRINT_FLAG_STACK |
				     STACK_PRINT_FLAG_HANDLE),
			    &page_owner_stack_fops);
	debugfs_create_file("count_threshold", 0600, dir, NULL,
			    &page_owner_threshold_fops);
	return 0;
}
late_initcall(pageowner_init)