percpu.c

/*
 * mm/percpu.c - percpu memory allocator
 *
 * Copyright (C) 2009		SUSE Linux Products GmbH
 * Copyright (C) 2009		Tejun Heo <tj@kernel.org>
 *
 * This file is released under the GPLv2 license.
 *
 * The percpu allocator handles both static and dynamic areas.  Percpu
 * areas are allocated in chunks which are divided into units.  There is
 * a 1-to-1 mapping for units to possible cpus.  These units are grouped
 * based on NUMA properties of the machine.
 *
 *  c0                           c1                         c2
 *  -------------------          -------------------        ------------
 * | u0 | u1 | u2 | u3 |        | u0 | u1 | u2 | u3 |      | u0 | u1 | u
 *  -------------------  ......  -------------------  ....  ------------
 *
 * Allocation is done by offsets into a unit's address space.  Ie., an
 * area of 512 bytes at 6k in c1 occupies 512 bytes at 6k in c1:u0,
 * c1:u1, c1:u2, etc.  On NUMA machines, the mapping may be non-linear
 * and even sparse.  Access is handled by configuring percpu base
 * registers according to the cpu to unit mappings and offsetting the
 * base address using pcpu_unit_size.
 *
 * There is special consideration for the first chunk which must handle
 * the static percpu variables in the kernel image as allocation services
 * are not online yet.  In short, the first chunk is structure like so:
 *
 *                  <Static | [Reserved] | Dynamic>
 *
 * The static data is copied from the original section managed by the
 * linker.  The reserved section, if non-zero, primarily manages static
 * percpu variables from kernel modules.  Finally, the dynamic section
 * takes care of normal allocations.
 *
 * Allocation state in each chunk is kept using an array of integers
 * on chunk->map.  A positive value in the map represents a free
 * region and negative allocated.  Allocation inside a chunk is done
 * by scanning this map sequentially and serving the first matching
 * entry.  This is mostly copied from the percpu_modalloc() allocator.
 * Chunks can be determined from the address using the index field
 * in the page struct. The index field contains a pointer to the chunk.
 *
 * These chunks are organized into lists according to free_size and
 * tries to allocate from the fullest chunk first. Each chunk maintains
 * a maximum contiguous area size hint which is guaranteed to be equal
 * to or larger than the maximum contiguous area in the chunk. This
 * helps prevent the allocator from iterating over chunks unnecessarily.
 *
 * To use this allocator, arch code should do the following:
 *
 * - define __addr_to_pcpu_ptr() and __pcpu_ptr_to_addr() to translate
 *   regular address to percpu pointer and back if they need to be
 *   different from the default
 *
 * - use pcpu_setup_first_chunk() during percpu area initialization to
 *   setup the first chunk containing the kernel static percpu area
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/bitmap.h>
#include <linux/bootmem.h>
#include <linux/err.h>
#include <linux/list.h>
#include <linux/log2.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/percpu.h>
#include <linux/pfn.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/vmalloc.h>
#include <linux/workqueue.h>
#include <linux/kmemleak.h>

#include <asm/cacheflush.h>
#include <asm/sections.h>
#include <asm/tlbflush.h>
#include <asm/io.h>

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

#include "percpu-internal.h"

#define PCPU_SLOT_BASE_SHIFT		5	/* 1-31 shares the same slot */
#define PCPU_DFL_MAP_ALLOC		16	/* start a map with 16 ents */
#define PCPU_ATOMIC_MAP_MARGIN_LOW	32
#define PCPU_ATOMIC_MAP_MARGIN_HIGH	64
#define PCPU_EMPTY_POP_PAGES_LOW	2
#define PCPU_EMPTY_POP_PAGES_HIGH	4

#ifdef CONFIG_SMP
/* default addr <-> pcpu_ptr mapping, override in asm/percpu.h if necessary */
#ifndef __addr_to_pcpu_ptr
#define __addr_to_pcpu_ptr(addr)					\
	(void __percpu *)((unsigned long)(addr) -			\
			  (unsigned long)pcpu_base_addr	+		\
			  (unsigned long)__per_cpu_start)
#endif
#ifndef __pcpu_ptr_to_addr
#define __pcpu_ptr_to_addr(ptr)						\
	(void __force *)((unsigned long)(ptr) +				\
			 (unsigned long)pcpu_base_addr -		\
			 (unsigned long)__per_cpu_start)
#endif
#else	/* CONFIG_SMP */
/* on UP, it's always identity mapped */
#define __addr_to_pcpu_ptr(addr)	(void __percpu *)(addr)
#define __pcpu_ptr_to_addr(ptr)		(void __force *)(ptr)
#endif	/* CONFIG_SMP */

static int pcpu_unit_pages __ro_after_init;
static int pcpu_unit_size __ro_after_init;
static int pcpu_nr_units __ro_after_init;
static int pcpu_atom_size __ro_after_init;
int pcpu_nr_slots __ro_after_init;
static size_t pcpu_chunk_struct_size __ro_after_init;

/* cpus with the lowest and highest unit addresses */
static unsigned int pcpu_low_unit_cpu __ro_after_init;
static unsigned int pcpu_high_unit_cpu __ro_after_init;

/* the address of the first chunk which starts with the kernel static area */
void *pcpu_base_addr __ro_after_init;
EXPORT_SYMBOL_GPL(pcpu_base_addr);

static const int *pcpu_unit_map __ro_after_init;		/* cpu -> unit */
const unsigned long *pcpu_unit_offsets __ro_after_init;	/* cpu -> unit offset */

/* group information, used for vm allocation */
static int pcpu_nr_groups __ro_after_init;
static const unsigned long *pcpu_group_offsets __ro_after_init;
static const size_t *pcpu_group_sizes __ro_after_init;

/*
 * The first chunk which always exists.  Note that unlike other
 * chunks, this one can be allocated and mapped in several different
 * ways and thus often doesn't live in the vmalloc area.
 */
struct pcpu_chunk *pcpu_first_chunk __ro_after_init;

/*
 * Optional reserved chunk.  This chunk reserves part of the first
 * chunk and serves it for reserved allocations.  When the reserved
 * region doesn't exist, the following variable is NULL.
 */
struct pcpu_chunk *pcpu_reserved_chunk __ro_after_init;

DEFINE_SPINLOCK(pcpu_lock);	/* all internal data structures */
static DEFINE_MUTEX(pcpu_alloc_mutex);	/* chunk create/destroy, [de]pop, map ext */

struct list_head *pcpu_slot __ro_after_init; /* chunk list slots */

/* chunks which need their map areas extended, protected by pcpu_lock */
static LIST_HEAD(pcpu_map_extend_chunks);

/*
 * The number of empty populated pages, protected by pcpu_lock.  The
 * reserved chunk doesn't contribute to the count.
 */
int pcpu_nr_empty_pop_pages;

/*
 * Balance work is used to populate or destroy chunks asynchronously.  We
 * try to keep the number of populated free pages between
 * PCPU_EMPTY_POP_PAGES_LOW and HIGH for atomic allocations and at most one
 * empty chunk.
 */
static void pcpu_balance_workfn(struct work_struct *work);
static DECLARE_WORK(pcpu_balance_work, pcpu_balance_workfn);
static bool pcpu_async_enabled __read_mostly;
static bool pcpu_atomic_alloc_failed;

static void pcpu_schedule_balance_work(void)
{
	if (pcpu_async_enabled)
		schedule_work(&pcpu_balance_work);
}

/**
 * pcpu_addr_in_chunk - check if the address is served from this chunk
 * @chunk: chunk of interest
 * @addr: percpu address
 *
 * RETURNS:
 * True if the address is served from this chunk.
 */
static bool pcpu_addr_in_chunk(struct pcpu_chunk *chunk, void *addr)
{
	void *start_addr, *end_addr;

	if (!chunk)
		return false;

	start_addr = chunk->base_addr + chunk->start_offset;
	end_addr = chunk->base_addr + chunk->nr_pages * PAGE_SIZE -
		   chunk->end_offset;

	return addr >= start_addr && addr < end_addr;
}

static int __pcpu_size_to_slot(int size)
{
	int highbit = fls(size);	/* size is in bytes */
	return max(highbit - PCPU_SLOT_BASE_SHIFT + 2, 1);
}

static int pcpu_size_to_slot(int size)
{
	if (size == pcpu_unit_size)
		return pcpu_nr_slots - 1;
	return __pcpu_size_to_slot(size);
}

static int pcpu_chunk_slot(const struct pcpu_chunk *chunk)
{
	if (chunk->free_size < sizeof(int) || chunk->contig_hint < sizeof(int))
		return 0;

	return pcpu_size_to_slot(chunk->free_size);
}

/* set the pointer to a chunk in a page struct */
static void pcpu_set_page_chunk(struct page *page, struct pcpu_chunk *pcpu)
{
	page->index = (unsigned long)pcpu;
}

/* obtain pointer to a chunk from a page struct */
static struct pcpu_chunk *pcpu_get_page_chunk(struct page *page)
{
	return (struct pcpu_chunk *)page->index;
}

static int __maybe_unused pcpu_page_idx(unsigned int cpu, int page_idx)
{
	return pcpu_unit_map[cpu] * pcpu_unit_pages + page_idx;
}

static unsigned long pcpu_unit_page_offset(unsigned int cpu, int page_idx)
{
	return pcpu_unit_offsets[cpu] + (page_idx << PAGE_SHIFT);
}

static unsigned long pcpu_chunk_addr(struct pcpu_chunk *chunk,
				     unsigned int cpu, int page_idx)
{
	return (unsigned long)chunk->base_addr +
	       pcpu_unit_page_offset(cpu, page_idx);
}

static void __maybe_unused pcpu_next_unpop(struct pcpu_chunk *chunk,
					   int *rs, int *re, int end)
{
	*rs = find_next_zero_bit(chunk->populated, end, *rs);
	*re = find_next_bit(chunk->populated, end, *rs + 1);
}

static void __maybe_unused pcpu_next_pop(struct pcpu_chunk *chunk,
					 int *rs, int *re, int end)
{
	*rs = find_next_bit(chunk->populated, end, *rs);
	*re = find_next_zero_bit(chunk->populated, end, *rs + 1);
}

/*
 * (Un)populated page region iterators.  Iterate over (un)populated
 * page regions between @start and @end in @chunk.  @rs and @re should
 * be integer variables and will be set to start and end page index of
 * the current region.
 */
#define pcpu_for_each_unpop_region(chunk, rs, re, start, end)		    \
	for ((rs) = (start), pcpu_next_unpop((chunk), &(rs), &(re), (end)); \
	     (rs) < (re);						    \
	     (rs) = (re) + 1, pcpu_next_unpop((chunk), &(rs), &(re), (end)))

#define pcpu_for_each_pop_region(chunk, rs, re, start, end)		    \
	for ((rs) = (start), pcpu_next_pop((chunk), &(rs), &(re), (end));   \
	     (rs) < (re);						    \
	     (rs) = (re) + 1, pcpu_next_pop((chunk), &(rs), &(re), (end)))

/**
 * pcpu_mem_zalloc - allocate memory
 * @size: bytes to allocate
 *
 * Allocate @size bytes.  If @size is smaller than PAGE_SIZE,
 * kzalloc() is used; otherwise, vzalloc() is used.  The returned
 * memory is always zeroed.
 *
 * CONTEXT:
 * Does GFP_KERNEL allocation.
 *
 * RETURNS:
 * Pointer to the allocated area on success, NULL on failure.
 */
static void *pcpu_mem_zalloc(size_t size)
{
	if (WARN_ON_ONCE(!slab_is_available()))
		return NULL;

	if (size <= PAGE_SIZE)
		return kzalloc(size, GFP_KERNEL);
	else
		return vzalloc(size);
}

/**
 * pcpu_mem_free - free memory
 * @ptr: memory to free
 *
 * Free @ptr.  @ptr should have been allocated using pcpu_mem_zalloc().
 */
static void pcpu_mem_free(void *ptr)
{
	kvfree(ptr);
}

/**
 * pcpu_count_occupied_pages - count the number of pages an area occupies
 * @chunk: chunk of interest
 * @i: index of the area in question
 *
 * Count the number of pages chunk's @i'th area occupies.  When the area's
 * start and/or end address isn't aligned to page boundary, the straddled
 * page is included in the count iff the rest of the page is free.
 */
static int pcpu_count_occupied_pages(struct pcpu_chunk *chunk, int i)
{
	int off = chunk->map[i] & ~1;
	int end = chunk->map[i + 1] & ~1;

	if (!PAGE_ALIGNED(off) && i > 0) {
		int prev = chunk->map[i - 1];

		if (!(prev & 1) && prev <= round_down(off, PAGE_SIZE))
			off = round_down(off, PAGE_SIZE);
	}

	if (!PAGE_ALIGNED(end) && i + 1 < chunk->map_used) {
		int next = chunk->map[i + 1];
		int nend = chunk->map[i + 2] & ~1;

		if (!(next & 1) && nend >= round_up(end, PAGE_SIZE))
			end = round_up(end, PAGE_SIZE);
	}

	return max_t(int, PFN_DOWN(end) - PFN_UP(off), 0);
}

/**
 * pcpu_chunk_relocate - put chunk in the appropriate chunk slot
 * @chunk: chunk of interest
 * @oslot: the previous slot it was on
 *
 * This function is called after an allocation or free changed @chunk.
 * New slot according to the changed state is determined and @chunk is
 * moved to the slot.  Note that the reserved chunk is never put on
 * chunk slots.
 *
 * CONTEXT:
 * pcpu_lock.
 */
static void pcpu_chunk_relocate(struct pcpu_chunk *chunk, int oslot)
{
	int nslot = pcpu_chunk_slot(chunk);

	if (chunk != pcpu_reserved_chunk && oslot != nslot) {
		if (oslot < nslot)
			list_move(&chunk->list, &pcpu_slot[nslot]);
		else
			list_move_tail(&chunk->list, &pcpu_slot[nslot]);
	}
}

/**
 * pcpu_need_to_extend - determine whether chunk area map needs to be extended
 * @chunk: chunk of interest
 * @is_atomic: the allocation context
 *
 * Determine whether area map of @chunk needs to be extended.  If
 * @is_atomic, only the amount necessary for a new allocation is
 * considered; however, async extension is scheduled if the left amount is
 * low.  If !@is_atomic, it aims for more empty space.  Combined, this
 * ensures that the map is likely to have enough available space to
 * accomodate atomic allocations which can't extend maps directly.
 *
 * CONTEXT:
 * pcpu_lock.
 *
 * RETURNS:
 * New target map allocation length if extension is necessary, 0
 * otherwise.
 */
static int pcpu_need_to_extend(struct pcpu_chunk *chunk, bool is_atomic)
{
	int margin, new_alloc;

	lockdep_assert_held(&pcpu_lock);

	if (is_atomic) {
		margin = 3;

		if (chunk->map_alloc <
		    chunk->map_used + PCPU_ATOMIC_MAP_MARGIN_LOW) {
			if (list_empty(&chunk->map_extend_list)) {
				list_add_tail(&chunk->map_extend_list,
					      &pcpu_map_extend_chunks);
				pcpu_schedule_balance_work();
			}
		}
	} else {
		margin = PCPU_ATOMIC_MAP_MARGIN_HIGH;
	}

	if (chunk->map_alloc >= chunk->map_used + margin)
		return 0;

	new_alloc = PCPU_DFL_MAP_ALLOC;
	while (new_alloc < chunk->map_used + margin)
		new_alloc *= 2;

	return new_alloc;
}

/**
 * pcpu_extend_area_map - extend area map of a chunk
 * @chunk: chunk of interest
 * @new_alloc: new target allocation length of the area map
 *
 * Extend area map of @chunk to have @new_alloc entries.
 *
 * CONTEXT:
 * Does GFP_KERNEL allocation.  Grabs and releases pcpu_lock.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
static int pcpu_extend_area_map(struct pcpu_chunk *chunk, int new_alloc)
{
	int *old = NULL, *new = NULL;
	size_t old_size = 0, new_size = new_alloc * sizeof(new[0]);
	unsigned long flags;

	lockdep_assert_held(&pcpu_alloc_mutex);

	new = pcpu_mem_zalloc(new_size);
	if (!new)
		return -ENOMEM;

	/* acquire pcpu_lock and switch to new area map */
	spin_lock_irqsave(&pcpu_lock, flags);

	if (new_alloc <= chunk->map_alloc)
		goto out_unlock;

	old_size = chunk->map_alloc * sizeof(chunk->map[0]);
	old = chunk->map;

	memcpy(new, old, old_size);

	chunk->map_alloc = new_alloc;
	chunk->map = new;
	new = NULL;

out_unlock:
	spin_unlock_irqrestore(&pcpu_lock, flags);

	/*
	 * pcpu_mem_free() might end up calling vfree() which uses
	 * IRQ-unsafe lock and thus can't be called under pcpu_lock.
	 */
	pcpu_mem_free(old);
	pcpu_mem_free(new);

	return 0;
}

/**
 * pcpu_fit_in_area - try to fit the requested allocation in a candidate area
 * @chunk: chunk the candidate area belongs to
 * @off: the offset to the start of the candidate area
 * @this_size: the size of the candidate area
 * @size: the size of the target allocation
 * @align: the alignment of the target allocation
 * @pop_only: only allocate from already populated region
 *
 * We're trying to allocate @size bytes aligned at @align.  @chunk's area
 * at @off sized @this_size is a candidate.  This function determines
 * whether the target allocation fits in the candidate area and returns the
 * number of bytes to pad after @off.  If the target area doesn't fit, -1
 * is returned.
 *
 * If @pop_only is %true, this function only considers the already
 * populated part of the candidate area.
 */
static int pcpu_fit_in_area(struct pcpu_chunk *chunk, int off, int this_size,
			    int size, int align, bool pop_only)
{
	int cand_off = off;

	while (true) {
		int head = ALIGN(cand_off, align) - off;
		int page_start, page_end, rs, re;

		if (this_size < head + size)
			return -1;

		if (!pop_only)
			return head;

		/*
		 * If the first unpopulated page is beyond the end of the
		 * allocation, the whole allocation is populated;
		 * otherwise, retry from the end of the unpopulated area.
		 */
		page_start = PFN_DOWN(head + off);
		page_end = PFN_UP(head + off + size);

		rs = page_start;
		pcpu_next_unpop(chunk, &rs, &re, PFN_UP(off + this_size));
		if (rs >= page_end)
			return head;
		cand_off = re * PAGE_SIZE;
	}
}

/**
 * pcpu_alloc_area - allocate area from a pcpu_chunk
 * @chunk: chunk of interest
 * @size: wanted size in bytes
 * @align: wanted align
 * @pop_only: allocate only from the populated area
 * @occ_pages_p: out param for the number of pages the area occupies
 *
 * Try to allocate @size bytes area aligned at @align from @chunk.
 * Note that this function only allocates the offset.  It doesn't
 * populate or map the area.
 *
 * @chunk->map must have at least two free slots.
 *
 * CONTEXT:
 * pcpu_lock.
 *
 * RETURNS:
 * Allocated offset in @chunk on success, -1 if no matching area is
 * found.
 */
static int pcpu_alloc_area(struct pcpu_chunk *chunk, int size, int align,
			   bool pop_only, int *occ_pages_p)
{
	int oslot = pcpu_chunk_slot(chunk);
	int max_contig = 0;
	int i, off;
	bool seen_free = false;
	int *p;

	for (i = chunk->first_free, p = chunk->map + i; i < chunk->map_used; i++, p++) {
		int head, tail;
		int this_size;

		off = *p;
		if (off & 1)
			continue;

		this_size = (p[1] & ~1) - off;

		head = pcpu_fit_in_area(chunk, off, this_size, size, align,
					pop_only);
		if (head < 0) {
			if (!seen_free) {
				chunk->first_free = i;
				seen_free = true;
			}
			max_contig = max(this_size, max_contig);
			continue;
		}

		/*
		 * If head is small or the previous block is free,
		 * merge'em.  Note that 'small' is defined as smaller
		 * than sizeof(int), which is very small but isn't too
		 * uncommon for percpu allocations.
		 */
		if (head && (head < sizeof(int) || !(p[-1] & 1))) {
			*p = off += head;
			if (p[-1] & 1)
				chunk->free_size -= head;
			else
				max_contig = max(*p - p[-1], max_contig);
			this_size -= head;
			head = 0;
		}

		/* if tail is small, just keep it around */
		tail = this_size - head - size;
		if (tail < sizeof(int)) {
			tail = 0;
			size = this_size - head;
		}

		/* split if warranted */
		if (head || tail) {
			int nr_extra = !!head + !!tail;

			/* insert new subblocks */
			memmove(p + nr_extra + 1, p + 1,
				sizeof(chunk->map[0]) * (chunk->map_used - i));
			chunk->map_used += nr_extra;

			if (head) {
				if (!seen_free) {
					chunk->first_free = i;
					seen_free = true;
				}
				*++p = off += head;
				++i;
				max_contig = max(head, max_contig);
			}
			if (tail) {
				p[1] = off + size;
				max_contig = max(tail, max_contig);
			}
		}

		if (!seen_free)
			chunk->first_free = i + 1;

		/* update hint and mark allocated */
		if (i + 1 == chunk->map_used)
			chunk->contig_hint = max_contig; /* fully scanned */
		else
			chunk->contig_hint = max(chunk->contig_hint,
						 max_contig);

		chunk->free_size -= size;
		*p |= 1;

		*occ_pages_p = pcpu_count_occupied_pages(chunk, i);
		pcpu_chunk_relocate(chunk, oslot);
		return off;
	}

	chunk->contig_hint = max_contig;	/* fully scanned */
	pcpu_chunk_relocate(chunk, oslot);

	/* tell the upper layer that this chunk has no matching area */
	return -1;
}

/**
 * pcpu_free_area - free area to a pcpu_chunk
 * @chunk: chunk of interest
 * @freeme: offset of area to free
 * @occ_pages_p: out param for the number of pages the area occupies
 *
 * Free area starting from @freeme to @chunk.  Note that this function
 * only modifies the allocation map.  It doesn't depopulate or unmap
 * the area.
 *
 * CONTEXT:
 * pcpu_lock.
 */
static void pcpu_free_area(struct pcpu_chunk *chunk, int freeme,
			   int *occ_pages_p)
{
	int oslot = pcpu_chunk_slot(chunk);
	int off = 0;
	unsigned i, j;
	int to_free = 0;
	int *p;

	lockdep_assert_held(&pcpu_lock);
	pcpu_stats_area_dealloc(chunk);

	freeme |= 1;	/* we are searching for <given offset, in use> pair */

	i = 0;
	j = chunk->map_used;
	while (i != j) {
		unsigned k = (i + j) / 2;
		off = chunk->map[k];
		if (off < freeme)
			i = k + 1;
		else if (off > freeme)
			j = k;
		else
			i = j = k;
	}
	BUG_ON(off != freeme);

	if (i < chunk->first_free)
		chunk->first_free = i;

	p = chunk->map + i;
	*p = off &= ~1;
	chunk->free_size += (p[1] & ~1) - off;

	*occ_pages_p = pcpu_count_occupied_pages(chunk, i);

	/* merge with next? */
	if (!(p[1] & 1))
		to_free++;
	/* merge with previous? */
	if (i > 0 && !(p[-1] & 1)) {
		to_free++;
		i--;
		p--;
	}
	if (to_free) {
		chunk->map_used -= to_free;
		memmove(p + 1, p + 1 + to_free,
			(chunk->map_used - i) * sizeof(chunk->map[0]));
	}

	chunk->contig_hint = max(chunk->map[i + 1] - chunk->map[i] - 1, chunk->contig_hint);
	pcpu_chunk_relocate(chunk, oslot);
}

static struct pcpu_chunk * __init pcpu_alloc_first_chunk(unsigned long tmp_addr,
							 int map_size,
							 int *map,
							 int init_map_size)
{
	struct pcpu_chunk *chunk;
	unsigned long aligned_addr;
	int start_offset, region_size;

	/* region calculations */
	aligned_addr = tmp_addr & PAGE_MASK;

	start_offset = tmp_addr - aligned_addr;

	region_size = PFN_ALIGN(start_offset + map_size);

	/* allocate chunk */
	chunk = memblock_virt_alloc(sizeof(struct pcpu_chunk) +
				    BITS_TO_LONGS(region_size >> PAGE_SHIFT),
				    0);

	INIT_LIST_HEAD(&chunk->list);
	INIT_LIST_HEAD(&chunk->map_extend_list);

	chunk->base_addr = (void *)aligned_addr;
	chunk->start_offset = start_offset;
	chunk->end_offset = region_size - chunk->start_offset - map_size;

	chunk->nr_pages = region_size >> PAGE_SHIFT;

	chunk->map = map;
	chunk->map_alloc = init_map_size;

	/* manage populated page bitmap */
	chunk->immutable = true;
	bitmap_fill(chunk->populated, chunk->nr_pages);
	chunk->nr_populated = chunk->nr_pages;
	chunk->nr_empty_pop_pages = chunk->nr_pages;

	chunk->contig_hint = chunk->free_size = map_size;

	if (chunk->start_offset) {
		/* hide the beginning of the bitmap */
		chunk->nr_empty_pop_pages--;

		chunk->map[0] = 1;
		chunk->map[1] = chunk->start_offset;
		chunk->map_used = 1;
	}

	/* set chunk's free region */
	chunk->map[++chunk->map_used] =
		(chunk->start_offset + chunk->free_size) | 1;

	if (chunk->end_offset) {
		/* hide the end of the bitmap */
		chunk->nr_empty_pop_pages--;

		chunk->map[++chunk->map_used] = region_size | 1;
	}

	return chunk;
}

static struct pcpu_chunk *pcpu_alloc_chunk(void)
{
	struct pcpu_chunk *chunk;

	chunk = pcpu_mem_zalloc(pcpu_chunk_struct_size);
	if (!chunk)
		return NULL;

	chunk->map = pcpu_mem_zalloc(PCPU_DFL_MAP_ALLOC *
						sizeof(chunk->map[0]));
	if (!chunk->map) {
		pcpu_mem_free(chunk);
		return NULL;
	}

	chunk->map_alloc = PCPU_DFL_MAP_ALLOC;
	chunk->map[0] = 0;
	chunk->map[1] = pcpu_unit_size | 1;
	chunk->map_used = 1;

	INIT_LIST_HEAD(&chunk->list);
	INIT_LIST_HEAD(&chunk->map_extend_list);
	chunk->free_size = pcpu_unit_size;
	chunk->contig_hint = pcpu_unit_size;

	chunk->nr_pages = pcpu_unit_pages;

	return chunk;
}

static void pcpu_free_chunk(struct pcpu_chunk *chunk)
{
	if (!chunk)
		return;
	pcpu_mem_free(chunk->map);
	pcpu_mem_free(chunk);
}

/**
 * pcpu_chunk_populated - post-population bookkeeping
 * @chunk: pcpu_chunk which got populated
 * @page_start: the start page
 * @page_end: the end page
 *
 * Pages in [@page_start,@page_end) have been populated to @chunk.  Update
 * the bookkeeping information accordingly.  Must be called after each
 * successful population.
 */
static void pcpu_chunk_populated(struct pcpu_chunk *chunk,
				 int page_start, int page_end)
{
	int nr = page_end - page_start;

	lockdep_assert_held(&pcpu_lock);

	bitmap_set(chunk->populated, page_start, nr);
	chunk->nr_populated += nr;
	chunk->nr_empty_pop_pages += nr;
	pcpu_nr_empty_pop_pages += nr;
}

/**
 * pcpu_chunk_depopulated - post-depopulation bookkeeping
 * @chunk: pcpu_chunk which got depopulated
 * @page_start: the start page
 * @page_end: the end page
 *
 * Pages in [@page_start,@page_end) have been depopulated from @chunk.
 * Update the bookkeeping information accordingly.  Must be called after
 * each successful depopulation.
 */
static void pcpu_chunk_depopulated(struct pcpu_chunk *chunk,
				   int page_start, int page_end)
{
	int nr = page_end - page_start;

	lockdep_assert_held(&pcpu_lock);

	bitmap_clear(chunk->populated, page_start, nr);
	chunk->nr_populated -= nr;
	chunk->nr_empty_pop_pages -= nr;
	pcpu_nr_empty_pop_pages -= nr;
}

/*
 * Chunk management implementation.
 *
 * To allow different implementations, chunk alloc/free and
 * [de]population are implemented in a separate file which is pulled
 * into this file and compiled together.  The following functions
 * should be implemented.
 *
 * pcpu_populate_chunk		- populate the specified range of a chunk
 * pcpu_depopulate_chunk	- depopulate the specified range of a chunk
 * pcpu_create_chunk		- create a new chunk
 * pcpu_destroy_chunk		- destroy a chunk, always preceded by full depop
 * pcpu_addr_to_page		- translate address to physical address
 * pcpu_verify_alloc_info	- check alloc_info is acceptable during init
 */
static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size);
static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk, int off, int size);
static struct pcpu_chunk *pcpu_create_chunk(void);
static void pcpu_destroy_chunk(struct pcpu_chunk *chunk);
static struct page *pcpu_addr_to_page(void *addr);
static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai);

#ifdef CONFIG_NEED_PER_CPU_KM
#include "percpu-km.c"
#else
#include "percpu-vm.c"
#endif

/**
 * pcpu_chunk_addr_search - determine chunk containing specified address
 * @addr: address for which the chunk needs to be determined.
 *
 * This is an internal function that handles all but static allocations.
 * Static percpu address values should never be passed into the allocator.
 *
 * RETURNS:
 * The address of the found chunk.
 */
static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
{
	/* is it in the dynamic region (first chunk)? */
	if (pcpu_addr_in_chunk(pcpu_first_chunk, addr))
		return pcpu_first_chunk;

	/* is it in the reserved region? */
	if (pcpu_addr_in_chunk(pcpu_reserved_chunk, addr))
		return pcpu_reserved_chunk;

	/*
	 * The address is relative to unit0 which might be unused and
	 * thus unmapped.  Offset the address to the unit space of the
	 * current processor before looking it up in the vmalloc
	 * space.  Note that any possible cpu id can be used here, so
	 * there's no need to worry about preemption or cpu hotplug.
	 */
	addr += pcpu_unit_offsets[raw_smp_processor_id()];
	return pcpu_get_page_chunk(pcpu_addr_to_page(addr));
}

/**
 * pcpu_alloc - the percpu allocator
 * @size: size of area to allocate in bytes
 * @align: alignment of area (max PAGE_SIZE)
 * @reserved: allocate from the reserved chunk if available
 * @gfp: allocation flags
 *
 * Allocate percpu area of @size bytes aligned at @align.  If @gfp doesn't
 * contain %GFP_KERNEL, the allocation is atomic.
 *
 * RETURNS:
 * Percpu pointer to the allocated area on success, NULL on failure.
 */
static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
				 gfp_t gfp)
{
	static int warn_limit = 10;
	struct pcpu_chunk *chunk;
	const char *err;
	bool is_atomic = (gfp & GFP_KERNEL) != GFP_KERNEL;
	int occ_pages = 0;
	int slot, off, new_alloc, cpu, ret;
	unsigned long flags;
	void __percpu *ptr;

	/*
	 * We want the lowest bit of offset available for in-use/free
	 * indicator, so force >= 16bit alignment and make size even.
	 */
	if (unlikely(align < PCPU_MIN_ALLOC_SIZE))
		align = PCPU_MIN_ALLOC_SIZE;

	size = ALIGN(size, PCPU_MIN_ALLOC_SIZE);

	if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE ||
		     !is_power_of_2(align))) {
		WARN(true, "illegal size (%zu) or align (%zu) for percpu allocation\n",
		     size, align);
		return NULL;
	}

	if (!is_atomic)
		mutex_lock(&pcpu_alloc_mutex);

	spin_lock_irqsave(&pcpu_lock, flags);

	/* serve reserved allocations from the reserved chunk if available */
	if (reserved && pcpu_reserved_chunk) {
		chunk = pcpu_reserved_chunk;

		if (size > chunk->contig_hint) {
			err = "alloc from reserved chunk failed";
			goto fail_unlock;
		}

		while ((new_alloc = pcpu_need_to_extend(chunk, is_atomic))) {
			spin_unlock_irqrestore(&pcpu_lock, flags);
			if (is_atomic ||
			    pcpu_extend_area_map(chunk, new_alloc) < 0) {
				err = "failed to extend area map of reserved chunk";
				goto fail;
			}
			spin_lock_irqsave(&pcpu_lock, flags);
		}

		off = pcpu_alloc_area(chunk, size, align, is_atomic,
				      &occ_pages);
		if (off >= 0)
			goto area_found;

		err = "alloc from reserved chunk failed";