percpu: add block level scan_hint

[linux.git] / mm / percpu.c

/*
 * mm/percpu.c - percpu memory allocator
 *
 * Copyright (C) 2009           SUSE Linux Products GmbH
 * Copyright (C) 2009           Tejun Heo <tj@kernel.org>
 *
 * Copyright (C) 2017           Facebook Inc.
 * Copyright (C) 2017           Dennis Zhou <dennisszhou@gmail.com>
 *
 * 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 structured 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.
 *
 * The allocator organizes chunks into lists according to free size and
 * tries to allocate from the fullest chunk first.  Each chunk is managed
 * by a bitmap with metadata blocks.  The allocation map is updated on
 * every allocation and free to reflect the current state while the boundary
 * map is only updated on allocation.  Each metadata block contains
 * information to help mitigate the need to iterate over large portions
 * of the bitmap.  The reverse mapping from page to chunk is stored in
 * the page's index.  Lastly, units are lazily backed and grow in unison.
 *
 * There is a unique conversion that goes on here between bytes and bits.
 * Each bit represents a fragment of size PCPU_MIN_ALLOC_SIZE.  The chunk
 * tracks the number of pages it is responsible for in nr_pages.  Helper
 * functions are used to convert from between the bytes, bits, and blocks.
 * All hints are managed in bits unless explicitly stated.
 *
 * 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/memblock.h>
#include <linux/err.h>
#include <linux/lcm.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 <linux/sched.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"

/* the slots are sorted by free bytes left, 1-31 bytes share the same slot */
#define PCPU_SLOT_BASE_SHIFT            5
/* chunks in slots below this are subject to being sidelined on failed alloc */
#define PCPU_SLOT_FAIL_THRESHOLD        3

#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;

/*
 * The number of populated pages in use by the allocator, protected by
 * pcpu_lock.  This number is kept per a unit per chunk (i.e. when a page gets
 * allocated/deallocated, it is allocated/deallocated in all units of a chunk
 * and increments/decrements this count by 1).
 */
static unsigned long pcpu_nr_populated;

/*
 * 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_bytes < PCPU_MIN_ALLOC_SIZE || chunk->contig_bits == 0)
                return 0;

        return pcpu_size_to_slot(chunk->contig_bits * PCPU_MIN_ALLOC_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 pcpu_next_unpop(unsigned long *bitmap, int *rs, int *re, int end)
{
        *rs = find_next_zero_bit(bitmap, end, *rs);
        *re = find_next_bit(bitmap, end, *rs + 1);
}

static void pcpu_next_pop(unsigned long *bitmap, int *rs, int *re, int end)
{
        *rs = find_next_bit(bitmap, end, *rs);
        *re = find_next_zero_bit(bitmap, end, *rs + 1);
}

/*
 * Bitmap region iterators.  Iterates over the bitmap between
 * [@start, @end) in @chunk.  @rs and @re should be integer variables
 * and will be set to start and end index of the current free region.
 */
#define pcpu_for_each_unpop_region(bitmap, rs, re, start, end)               \
        for ((rs) = (start), pcpu_next_unpop((bitmap), &(rs), &(re), (end)); \
             (rs) < (re);                                                    \
             (rs) = (re) + 1, pcpu_next_unpop((bitmap), &(rs), &(re), (end)))

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

/*
 * The following are helper functions to help access bitmaps and convert
 * between bitmap offsets to address offsets.
 */
static unsigned long *pcpu_index_alloc_map(struct pcpu_chunk *chunk, int index)
{
        return chunk->alloc_map +
               (index * PCPU_BITMAP_BLOCK_BITS / BITS_PER_LONG);
}

static unsigned long pcpu_off_to_block_index(int off)
{
        return off / PCPU_BITMAP_BLOCK_BITS;
}

static unsigned long pcpu_off_to_block_off(int off)
{
        return off & (PCPU_BITMAP_BLOCK_BITS - 1);
}

static unsigned long pcpu_block_off_to_off(int index, int off)
{
        return index * PCPU_BITMAP_BLOCK_BITS + off;
}

/*
 * pcpu_next_hint - determine which hint to use
 * @block: block of interest
 * @alloc_bits: size of allocation
 *
 * This determines if we should scan based on the scan_hint or first_free.
 * In general, we want to scan from first_free to fulfill allocations by
 * first fit.  However, if we know a scan_hint at position scan_hint_start
 * cannot fulfill an allocation, we can begin scanning from there knowing
 * the contig_hint will be our fallback.
 */
static int pcpu_next_hint(struct pcpu_block_md *block, int alloc_bits)
{
        /*
         * The three conditions below determine if we can skip past the
         * scan_hint.  First, does the scan hint exist.  Second, is the
         * contig_hint after the scan_hint (possibly not true iff
         * contig_hint == scan_hint).  Third, is the allocation request
         * larger than the scan_hint.
         */
        if (block->scan_hint &&
            block->contig_hint_start > block->scan_hint_start &&
            alloc_bits > block->scan_hint)
                return block->scan_hint_start + block->scan_hint;

        return block->first_free;
}

/**
 * pcpu_next_md_free_region - finds the next hint free area
 * @chunk: chunk of interest
 * @bit_off: chunk offset
 * @bits: size of free area
 *
 * Helper function for pcpu_for_each_md_free_region.  It checks
 * block->contig_hint and performs aggregation across blocks to find the
 * next hint.  It modifies bit_off and bits in-place to be consumed in the
 * loop.
 */
static void pcpu_next_md_free_region(struct pcpu_chunk *chunk, int *bit_off,
                                     int *bits)
{
        int i = pcpu_off_to_block_index(*bit_off);
        int block_off = pcpu_off_to_block_off(*bit_off);
        struct pcpu_block_md *block;

        *bits = 0;
        for (block = chunk->md_blocks + i; i < pcpu_chunk_nr_blocks(chunk);
             block++, i++) {
                /* handles contig area across blocks */
                if (*bits) {
                        *bits += block->left_free;
                        if (block->left_free == PCPU_BITMAP_BLOCK_BITS)
                                continue;
                        return;
                }

                /*
                 * This checks three things.  First is there a contig_hint to
                 * check.  Second, have we checked this hint before by
                 * comparing the block_off.  Third, is this the same as the
                 * right contig hint.  In the last case, it spills over into
                 * the next block and should be handled by the contig area
                 * across blocks code.
                 */
                *bits = block->contig_hint;
                if (*bits && block->contig_hint_start >= block_off &&
                    *bits + block->contig_hint_start < PCPU_BITMAP_BLOCK_BITS) {
                        *bit_off = pcpu_block_off_to_off(i,
                                        block->contig_hint_start);
                        return;
                }
                /* reset to satisfy the second predicate above */
                block_off = 0;

                *bits = block->right_free;
                *bit_off = (i + 1) * PCPU_BITMAP_BLOCK_BITS - block->right_free;
        }
}

/**
 * pcpu_next_fit_region - finds fit areas for a given allocation request
 * @chunk: chunk of interest
 * @alloc_bits: size of allocation
 * @align: alignment of area (max PAGE_SIZE)
 * @bit_off: chunk offset
 * @bits: size of free area
 *
 * Finds the next free region that is viable for use with a given size and
 * alignment.  This only returns if there is a valid area to be used for this
 * allocation.  block->first_free is returned if the allocation request fits
 * within the block to see if the request can be fulfilled prior to the contig
 * hint.
 */
static void pcpu_next_fit_region(struct pcpu_chunk *chunk, int alloc_bits,
                                 int align, int *bit_off, int *bits)
{
        int i = pcpu_off_to_block_index(*bit_off);
        int block_off = pcpu_off_to_block_off(*bit_off);
        struct pcpu_block_md *block;

        *bits = 0;
        for (block = chunk->md_blocks + i; i < pcpu_chunk_nr_blocks(chunk);
             block++, i++) {
                /* handles contig area across blocks */
                if (*bits) {
                        *bits += block->left_free;
                        if (*bits >= alloc_bits)
                                return;
                        if (block->left_free == PCPU_BITMAP_BLOCK_BITS)
                                continue;
                }

                /* check block->contig_hint */
                *bits = ALIGN(block->contig_hint_start, align) -
                        block->contig_hint_start;
                /*
                 * This uses the block offset to determine if this has been
                 * checked in the prior iteration.
                 */
                if (block->contig_hint &&
                    block->contig_hint_start >= block_off &&
                    block->contig_hint >= *bits + alloc_bits) {
                        int start = pcpu_next_hint(block, alloc_bits);

                        *bits += alloc_bits + block->contig_hint_start -
                                 start;
                        *bit_off = pcpu_block_off_to_off(i, start);
                        return;
                }
                /* reset to satisfy the second predicate above */
                block_off = 0;

                *bit_off = ALIGN(PCPU_BITMAP_BLOCK_BITS - block->right_free,
                                 align);
                *bits = PCPU_BITMAP_BLOCK_BITS - *bit_off;
                *bit_off = pcpu_block_off_to_off(i, *bit_off);
                if (*bits >= alloc_bits)
                        return;
        }

        /* no valid offsets were found - fail condition */
        *bit_off = pcpu_chunk_map_bits(chunk);
}

/*
 * Metadata free area iterators.  These perform aggregation of free areas
 * based on the metadata blocks and return the offset @bit_off and size in
 * bits of the free area @bits.  pcpu_for_each_fit_region only returns when
 * a fit is found for the allocation request.
 */
#define pcpu_for_each_md_free_region(chunk, bit_off, bits)              \
        for (pcpu_next_md_free_region((chunk), &(bit_off), &(bits));    \
             (bit_off) < pcpu_chunk_map_bits((chunk));                  \
             (bit_off) += (bits) + 1,                                   \
             pcpu_next_md_free_region((chunk), &(bit_off), &(bits)))

#define pcpu_for_each_fit_region(chunk, alloc_bits, align, bit_off, bits)     \
        for (pcpu_next_fit_region((chunk), (alloc_bits), (align), &(bit_off), \
                                  &(bits));                                   \
             (bit_off) < pcpu_chunk_map_bits((chunk));                        \
             (bit_off) += (bits),                                             \
             pcpu_next_fit_region((chunk), (alloc_bits), (align), &(bit_off), \
                                  &(bits)))

/**
 * pcpu_mem_zalloc - allocate memory
 * @size: bytes to allocate
 * @gfp: allocation flags
 *
 * Allocate @size bytes.  If @size is smaller than PAGE_SIZE,
 * kzalloc() is used; otherwise, the equivalent of vzalloc() is used.
 * This is to facilitate passing through whitelisted flags.  The
 * returned memory is always zeroed.
 *
 * RETURNS:
 * Pointer to the allocated area on success, NULL on failure.
 */
static void *pcpu_mem_zalloc(size_t size, gfp_t gfp)
{
        if (WARN_ON_ONCE(!slab_is_available()))
                return NULL;

        if (size <= PAGE_SIZE)
                return kzalloc(size, gfp);
        else
                return __vmalloc(size, gfp | __GFP_ZERO, PAGE_KERNEL);
}

/**
 * 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);
}

static void __pcpu_chunk_move(struct pcpu_chunk *chunk, int slot,
                              bool move_front)
{
        if (chunk != pcpu_reserved_chunk) {
                if (move_front)
                        list_move(&chunk->list, &pcpu_slot[slot]);
                else
                        list_move_tail(&chunk->list, &pcpu_slot[slot]);
        }
}

static void pcpu_chunk_move(struct pcpu_chunk *chunk, int slot)
{
        __pcpu_chunk_move(chunk, slot, true);
}

/**
 * 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 (oslot != nslot)
                __pcpu_chunk_move(chunk, nslot, oslot < nslot);
}

/*
 * pcpu_update_empty_pages - update empty page counters
 * @chunk: chunk of interest
 * @nr: nr of empty pages
 *
 * This is used to keep track of the empty pages now based on the premise
 * a md_block covers a page.  The hint update functions recognize if a block
 * is made full or broken to calculate deltas for keeping track of free pages.
 */
static inline void pcpu_update_empty_pages(struct pcpu_chunk *chunk, int nr)
{
        chunk->nr_empty_pop_pages += nr;
        if (chunk != pcpu_reserved_chunk)
                pcpu_nr_empty_pop_pages += nr;
}

/*
 * pcpu_region_overlap - determines if two regions overlap
 * @a: start of first region, inclusive
 * @b: end of first region, exclusive
 * @x: start of second region, inclusive
 * @y: end of second region, exclusive
 *
 * This is used to determine if the hint region [a, b) overlaps with the
 * allocated region [x, y).
 */
static inline bool pcpu_region_overlap(int a, int b, int x, int y)
{
        return (a < y) && (x < b);
}

/**
 * pcpu_chunk_update - updates the chunk metadata given a free area
 * @chunk: chunk of interest
 * @bit_off: chunk offset
 * @bits: size of free area
 *
 * This updates the chunk's contig hint and starting offset given a free area.
 * Choose the best starting offset if the contig hint is equal.
 */
static void pcpu_chunk_update(struct pcpu_chunk *chunk, int bit_off, int bits)
{
        if (bits > chunk->contig_bits) {
                chunk->contig_bits_start = bit_off;
                chunk->contig_bits = bits;
        } else if (bits == chunk->contig_bits && chunk->contig_bits_start &&
                   (!bit_off ||
                    __ffs(bit_off) > __ffs(chunk->contig_bits_start))) {
                /* use the start with the best alignment */
                chunk->contig_bits_start = bit_off;
        }
}

/**
 * pcpu_chunk_refresh_hint - updates metadata about a chunk
 * @chunk: chunk of interest
 *
 * Iterates over the metadata blocks to find the largest contig area.
 * It also counts the populated pages and uses the delta to update the
 * global count.
 *
 * Updates:
 *      chunk->contig_bits
 *      chunk->contig_bits_start
 */
static void pcpu_chunk_refresh_hint(struct pcpu_chunk *chunk)
{
        int bit_off, bits;

        /* clear metadata */
        chunk->contig_bits = 0;

        bit_off = chunk->first_bit;
        bits = 0;
        pcpu_for_each_md_free_region(chunk, bit_off, bits) {
                pcpu_chunk_update(chunk, bit_off, bits);
        }
}

/**
 * pcpu_block_update - updates a block given a free area
 * @block: block of interest
 * @start: start offset in block
 * @end: end offset in block
 *
 * Updates a block given a known free area.  The region [start, end) is
 * expected to be the entirety of the free area within a block.  Chooses
 * the best starting offset if the contig hints are equal.
 */
static void pcpu_block_update(struct pcpu_block_md *block, int start, int end)
{
        int contig = end - start;

        block->first_free = min(block->first_free, start);
        if (start == 0)
                block->left_free = contig;

        if (end == PCPU_BITMAP_BLOCK_BITS)
                block->right_free = contig;

        if (contig > block->contig_hint) {
                /* promote the old contig_hint to be the new scan_hint */
                if (start > block->contig_hint_start) {
                        if (block->contig_hint > block->scan_hint) {
                                block->scan_hint_start =
                                        block->contig_hint_start;
                                block->scan_hint = block->contig_hint;
                        } else if (start < block->scan_hint_start) {
                                /*
                                 * The old contig_hint == scan_hint.  But, the
                                 * new contig is larger so hold the invariant
                                 * scan_hint_start < contig_hint_start.
                                 */
                                block->scan_hint = 0;
                        }
                } else {
                        block->scan_hint = 0;
                }
                block->contig_hint_start = start;
                block->contig_hint = contig;
        } else if (contig == block->contig_hint) {
                if (block->contig_hint_start &&
                    (!start ||
                     __ffs(start) > __ffs(block->contig_hint_start))) {
                        /* start has a better alignment so use it */
                        block->contig_hint_start = start;
                        if (start < block->scan_hint_start &&
                            block->contig_hint > block->scan_hint)
                                block->scan_hint = 0;
                } else if (start > block->scan_hint_start ||
                           block->contig_hint > block->scan_hint) {
                        /*
                         * Knowing contig == contig_hint, update the scan_hint
                         * if it is farther than or larger than the current
                         * scan_hint.
                         */
                        block->scan_hint_start = start;
                        block->scan_hint = contig;
                }
        } else {
                /*
                 * The region is smaller than the contig_hint.  So only update
                 * the scan_hint if it is larger than or equal and farther than
                 * the current scan_hint.
                 */
                if ((start < block->contig_hint_start &&
                     (contig > block->scan_hint ||
                      (contig == block->scan_hint &&
                       start > block->scan_hint_start)))) {
                        block->scan_hint_start = start;
                        block->scan_hint = contig;
                }
        }
}

/**
 * pcpu_block_refresh_hint
 * @chunk: chunk of interest
 * @index: index of the metadata block
 *
 * Scans over the block beginning at first_free and updates the block
 * metadata accordingly.
 */
static void pcpu_block_refresh_hint(struct pcpu_chunk *chunk, int index)
{
        struct pcpu_block_md *block = chunk->md_blocks + index;
        unsigned long *alloc_map = pcpu_index_alloc_map(chunk, index);
        int rs, re;     /* region start, region end */

        /* clear hints */
        block->contig_hint = block->scan_hint = 0;
        block->left_free = block->right_free = 0;

        /* iterate over free areas and update the contig hints */
        pcpu_for_each_unpop_region(alloc_map, rs, re, block->first_free,
                                   PCPU_BITMAP_BLOCK_BITS) {
                pcpu_block_update(block, rs, re);
        }
}

/**
 * pcpu_block_update_hint_alloc - update hint on allocation path
 * @chunk: chunk of interest
 * @bit_off: chunk offset
 * @bits: size of request
 *
 * Updates metadata for the allocation path.  The metadata only has to be
 * refreshed by a full scan iff the chunk's contig hint is broken.  Block level
 * scans are required if the block's contig hint is broken.
 */
static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off,
                                         int bits)
{
        int nr_empty_pages = 0;
        struct pcpu_block_md *s_block, *e_block, *block;
        int s_index, e_index;   /* block indexes of the freed allocation */
        int s_off, e_off;       /* block offsets of the freed allocation */

        /*
         * Calculate per block offsets.
         * The calculation uses an inclusive range, but the resulting offsets
         * are [start, end).  e_index always points to the last block in the
         * range.
         */
        s_index = pcpu_off_to_block_index(bit_off);
        e_index = pcpu_off_to_block_index(bit_off + bits - 1);
        s_off = pcpu_off_to_block_off(bit_off);
        e_off = pcpu_off_to_block_off(bit_off + bits - 1) + 1;

        s_block = chunk->md_blocks + s_index;
        e_block = chunk->md_blocks + e_index;

        /*
         * Update s_block.
         * block->first_free must be updated if the allocation takes its place.
         * If the allocation breaks the contig_hint, a scan is required to
         * restore this hint.
         */
        if (s_block->contig_hint == PCPU_BITMAP_BLOCK_BITS)
                nr_empty_pages++;

        if (s_off == s_block->first_free)
                s_block->first_free = find_next_zero_bit(
                                        pcpu_index_alloc_map(chunk, s_index),
                                        PCPU_BITMAP_BLOCK_BITS,
                                        s_off + bits);

        if (pcpu_region_overlap(s_block->scan_hint_start,
                                s_block->scan_hint_start + s_block->scan_hint,
                                s_off,
                                s_off + bits))
                s_block->scan_hint = 0;

        if (pcpu_region_overlap(s_block->contig_hint_start,
                                s_block->contig_hint_start +
                                s_block->contig_hint,
                                s_off,
                                s_off + bits)) {
                /* block contig hint is broken - scan to fix it */
                pcpu_block_refresh_hint(chunk, s_index);
        } else {
                /* update left and right contig manually */
                s_block->left_free = min(s_block->left_free, s_off);
                if (s_index == e_index)
                        s_block->right_free = min_t(int, s_block->right_free,
                                        PCPU_BITMAP_BLOCK_BITS - e_off);
                else
                        s_block->right_free = 0;
        }

        /*
         * Update e_block.
         */
        if (s_index != e_index) {
                if (e_block->contig_hint == PCPU_BITMAP_BLOCK_BITS)
                        nr_empty_pages++;

                /*
                 * When the allocation is across blocks, the end is along
                 * the left part of the e_block.
                 */
                e_block->first_free = find_next_zero_bit(
                                pcpu_index_alloc_map(chunk, e_index),
                                PCPU_BITMAP_BLOCK_BITS, e_off);

                if (e_off == PCPU_BITMAP_BLOCK_BITS) {
                        /* reset the block */
                        e_block++;
                } else {
                        if (e_off > e_block->scan_hint_start)
                                e_block->scan_hint = 0;

                        if (e_off > e_block->contig_hint_start) {
                                /* contig hint is broken - scan to fix it */
                                pcpu_block_refresh_hint(chunk, e_index);
                        } else {
                                e_block->left_free = 0;
                                e_block->right_free =
                                        min_t(int, e_block->right_free,
                                              PCPU_BITMAP_BLOCK_BITS - e_off);
                        }
                }

                /* update in-between md_blocks */
                nr_empty_pages += (e_index - s_index - 1);
                for (block = s_block + 1; block < e_block; block++) {
                        block->scan_hint = 0;
                        block->contig_hint = 0;
                        block->left_free = 0;
                        block->right_free = 0;
                }
        }

        if (nr_empty_pages)
                pcpu_update_empty_pages(chunk, -nr_empty_pages);

        /*
         * The only time a full chunk scan is required is if the chunk
         * contig hint is broken.  Otherwise, it means a smaller space
         * was used and therefore the chunk contig hint is still correct.
         */
        if (pcpu_region_overlap(chunk->contig_bits_start,
                                chunk->contig_bits_start + chunk->contig_bits,
                                bit_off,
                                bit_off + bits))
                pcpu_chunk_refresh_hint(chunk);
}

/**
 * pcpu_block_update_hint_free - updates the block hints on the free path
 * @chunk: chunk of interest
 * @bit_off: chunk offset
 * @bits: size of request
 *
 * Updates metadata for the allocation path.  This avoids a blind block
 * refresh by making use of the block contig hints.  If this fails, it scans
 * forward and backward to determine the extent of the free area.  This is
 * capped at the boundary of blocks.
 *
 * A chunk update is triggered if a page becomes free, a block becomes free,
 * or the free spans across blocks.  This tradeoff is to minimize iterating
 * over the block metadata to update chunk->contig_bits.  chunk->contig_bits
 * may be off by up to a page, but it will never be more than the available
 * space.  If the contig hint is contained in one block, it will be accurate.
 */
static void pcpu_block_update_hint_free(struct pcpu_chunk *chunk, int bit_off,
                                        int bits)
{
        int nr_empty_pages = 0;
        struct pcpu_block_md *s_block, *e_block, *block;
        int s_index, e_index;   /* block indexes of the freed allocation */
        int s_off, e_off;       /* block offsets of the freed allocation */
        int start, end;         /* start and end of the whole free area */

        /*
         * Calculate per block offsets.
         * The calculation uses an inclusive range, but the resulting offsets
         * are [start, end).  e_index always points to the last block in the
         * range.
         */
        s_index = pcpu_off_to_block_index(bit_off);
        e_index = pcpu_off_to_block_index(bit_off + bits - 1);
        s_off = pcpu_off_to_block_off(bit_off);
        e_off = pcpu_off_to_block_off(bit_off + bits - 1) + 1;

        s_block = chunk->md_blocks + s_index;
        e_block = chunk->md_blocks + e_index;

        /*
         * Check if the freed area aligns with the block->contig_hint.
         * If it does, then the scan to find the beginning/end of the
         * larger free area can be avoided.
         *
         * start and end refer to beginning and end of the free area
         * within each their respective blocks.  This is not necessarily
         * the entire free area as it may span blocks past the beginning
         * or end of the block.
         */
        start = s_off;
        if (s_off == s_block->contig_hint + s_block->contig_hint_start) {
                start = s_block->contig_hint_start;
        } else {
                /*
                 * Scan backwards to find the extent of the free area.
                 * find_last_bit returns the starting bit, so if the start bit
                 * is returned, that means there was no last bit and the
                 * remainder of the chunk is free.
                 */
                int l_bit = find_last_bit(pcpu_index_alloc_map(chunk, s_index),
                                          start);
                start = (start == l_bit) ? 0 : l_bit + 1;
        }

        end = e_off;
        if (e_off == e_block->contig_hint_start)
                end = e_block->contig_hint_start + e_block->contig_hint;
        else
                end = find_next_bit(pcpu_index_alloc_map(chunk, e_index),
                                    PCPU_BITMAP_BLOCK_BITS, end);

        /* update s_block */
        e_off = (s_index == e_index) ? end : PCPU_BITMAP_BLOCK_BITS;
        if (!start && e_off == PCPU_BITMAP_BLOCK_BITS)
                nr_empty_pages++;
        pcpu_block_update(s_block, start, e_off);

        /* freeing in the same block */
        if (s_index != e_index) {
                /* update e_block */
                if (end == PCPU_BITMAP_BLOCK_BITS)
                        nr_empty_pages++;
                pcpu_block_update(e_block, 0, end);

                /* reset md_blocks in the middle */
                nr_empty_pages += (e_index - s_index - 1);
                for (block = s_block + 1; block < e_block; block++) {
                        block->first_free = 0;
                        block->scan_hint = 0;
                        block->contig_hint_start = 0;
                        block->contig_hint = PCPU_BITMAP_BLOCK_BITS;
                        block->left_free = PCPU_BITMAP_BLOCK_BITS;
                        block->right_free = PCPU_BITMAP_BLOCK_BITS;
                }
        }

        if (nr_empty_pages)
                pcpu_update_empty_pages(chunk, nr_empty_pages);

        /*
         * Refresh chunk metadata when the free makes a block free or spans
         * across blocks.  The contig_hint may be off by up to a page, but if
         * the contig_hint is contained in a block, it will be accurate with
         * the else condition below.
         */
        if (((end - start) >= PCPU_BITMAP_BLOCK_BITS) || s_index != e_index)
                pcpu_chunk_refresh_hint(chunk);
        else
                pcpu_chunk_update(chunk, pcpu_block_off_to_off(s_index, start),
                                  end - start);
}

/**
 * pcpu_is_populated - determines if the region is populated
 * @chunk: chunk of interest
 * @bit_off: chunk offset
 * @bits: size of area
 * @next_off: return value for the next offset to start searching
 *
 * For atomic allocations, check if the backing pages are populated.
 *
 * RETURNS:
 * Bool if the backing pages are populated.
 * next_index is to skip over unpopulated blocks in pcpu_find_block_fit.
 */
static bool pcpu_is_populated(struct pcpu_chunk *chunk, int bit_off, int bits,
                              int *next_off)
{
        int page_start, page_end, rs, re;

        page_start = PFN_DOWN(bit_off * PCPU_MIN_ALLOC_SIZE);
        page_end = PFN_UP((bit_off + bits) * PCPU_MIN_ALLOC_SIZE);

        rs = page_start;
        pcpu_next_unpop(chunk->populated, &rs, &re, page_end);
        if (rs >= page_end)
                return true;

        *next_off = re * PAGE_SIZE / PCPU_MIN_ALLOC_SIZE;
        return false;
}

/**
 * pcpu_find_block_fit - finds the block index to start searching
 * @chunk: chunk of interest
 * @alloc_bits: size of request in allocation units
 * @align: alignment of area (max PAGE_SIZE bytes)
 * @pop_only: use populated regions only
 *
 * Given a chunk and an allocation spec, find the offset to begin searching
 * for a free region.  This iterates over the bitmap metadata blocks to
 * find an offset that will be guaranteed to fit the requirements.  It is
 * not quite first fit as if the allocation does not fit in the contig hint
 * of a block or chunk, it is skipped.  This errs on the side of caution
 * to prevent excess iteration.  Poor alignment can cause the allocator to
 * skip over blocks and chunks that have valid free areas.
 *
 * RETURNS:
 * The offset in the bitmap to begin searching.
 * -1 if no offset is found.
 */
static int pcpu_find_block_fit(struct pcpu_chunk *chunk, int alloc_bits,
                               size_t align, bool pop_only)
{
        int bit_off, bits, next_off;

        /*
         * Check to see if the allocation can fit in the chunk's contig hint.
         * This is an optimization to prevent scanning by assuming if it
         * cannot fit in the global hint, there is memory pressure and creating
         * a new chunk would happen soon.
         */
        bit_off = ALIGN(chunk->contig_bits_start, align) -
                  chunk->contig_bits_start;
        if (bit_off + alloc_bits > chunk->contig_bits)
                return -1;

        bit_off = chunk->first_bit;
        bits = 0;
        pcpu_for_each_fit_region(chunk, alloc_bits, align, bit_off, bits) {
                if (!pop_only || pcpu_is_populated(chunk, bit_off, bits,
                                                   &next_off))
                        break;

                bit_off = next_off;
                bits = 0;
        }

        if (bit_off == pcpu_chunk_map_bits(chunk))
                return -1;

        return bit_off;
}

/**
 * pcpu_alloc_area - allocates an area from a pcpu_chunk
 * @chunk: chunk of interest
 * @alloc_bits: size of request in allocation units
 * @align: alignment of area (max PAGE_SIZE)
 * @start: bit_off to start searching
 *
 * This function takes in a @start offset to begin searching to fit an
 * allocation of @alloc_bits with alignment @align.  It needs to scan
 * the allocation map because if it fits within the block's contig hint,
 * @start will be block->first_free. This is an attempt to fill the
 * allocation prior to breaking the contig hint.  The allocation and
 * boundary maps are updated accordingly if it confirms a valid
 * free area.
 *
 * RETURNS:
 * Allocated addr offset in @chunk on success.
 * -1 if no matching area is found.
 */
static int pcpu_alloc_area(struct pcpu_chunk *chunk, int alloc_bits,
                           size_t align, int start)
{
        size_t align_mask = (align) ? (align - 1) : 0;
        int bit_off, end, oslot;

        lockdep_assert_held(&pcpu_lock);

        oslot = pcpu_chunk_slot(chunk);

        /*
         * Search to find a fit.
         */
        end = min_t(int, start + alloc_bits + PCPU_BITMAP_BLOCK_BITS,
                    pcpu_chunk_map_bits(chunk));
        bit_off = bitmap_find_next_zero_area(chunk->alloc_map, end, start,
                                             alloc_bits, align_mask);
        if (bit_off >= end)
                return -1;

        /* update alloc map */
        bitmap_set(chunk->alloc_map, bit_off, alloc_bits);

        /* update boundary map */
        set_bit(bit_off, chunk->bound_map);
        bitmap_clear(chunk->bound_map, bit_off + 1, alloc_bits - 1);
        set_bit(bit_off + alloc_bits, chunk->bound_map);

        chunk->free_bytes -= alloc_bits * PCPU_MIN_ALLOC_SIZE;

        /* update first free bit */
        if (bit_off == chunk->first_bit)
                chunk->first_bit = find_next_zero_bit(
                                        chunk->alloc_map,
                                        pcpu_chunk_map_bits(chunk),
                                        bit_off + alloc_bits);

        pcpu_block_update_hint_alloc(chunk, bit_off, alloc_bits);

        pcpu_chunk_relocate(chunk, oslot);

        return bit_off * PCPU_MIN_ALLOC_SIZE;
}

/**
 * pcpu_free_area - frees the corresponding offset
 * @chunk: chunk of interest
 * @off: addr offset into chunk
 *
 * This function determines the size of an allocation to free using
 * the boundary bitmap and clears the allocation map.
 */
static void pcpu_free_area(struct pcpu_chunk *chunk, int off)
{
        int bit_off, bits, end, oslot;

        lockdep_assert_held(&pcpu_lock);
        pcpu_stats_area_dealloc(chunk);

        oslot = pcpu_chunk_slot(chunk);

        bit_off = off / PCPU_MIN_ALLOC_SIZE;

        /* find end index */
        end = find_next_bit(chunk->bound_map, pcpu_chunk_map_bits(chunk),
                            bit_off + 1);
        bits = end - bit_off;
        bitmap_clear(chunk->alloc_map, bit_off, bits);

        /* update metadata */
        chunk->free_bytes += bits * PCPU_MIN_ALLOC_SIZE;

        /* update first free bit */
        chunk->first_bit = min(chunk->first_bit, bit_off);

        pcpu_block_update_hint_free(chunk, bit_off, bits);

        pcpu_chunk_relocate(chunk, oslot);
}

static void pcpu_init_md_blocks(struct pcpu_chunk *chunk)
{
        struct pcpu_block_md *md_block;

        for (md_block = chunk->md_blocks;
             md_block != chunk->md_blocks + pcpu_chunk_nr_blocks(chunk);
             md_block++) {
                md_block->scan_hint = 0;
                md_block->contig_hint = PCPU_BITMAP_BLOCK_BITS;
                md_block->left_free = PCPU_BITMAP_BLOCK_BITS;
                md_block->right_free = PCPU_BITMAP_BLOCK_BITS;
        }
}

/**
 * pcpu_alloc_first_chunk - creates chunks that serve the first chunk
 * @tmp_addr: the start of the region served
 * @map_size: size of the region served
 *
 * This is responsible for creating the chunks that serve the first chunk.  The
 * base_addr is page aligned down of @tmp_addr while the region end is page
 * aligned up.  Offsets are kept track of to determine the region served. All
 * this is done to appease the bitmap allocator in avoiding partial blocks.
 *
 * RETURNS:
 * Chunk serving the region at @tmp_addr of @map_size.
 */
static struct pcpu_chunk * __init pcpu_alloc_first_chunk(unsigned long tmp_addr,
                                                         int map_size)
{
        struct pcpu_chunk *chunk;
        unsigned long aligned_addr, lcm_align;
        int start_offset, offset_bits, region_size, region_bits;
        size_t alloc_size;

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

        start_offset = tmp_addr - aligned_addr;

        /*
         * Align the end of the region with the LCM of PAGE_SIZE and
         * PCPU_BITMAP_BLOCK_SIZE.  One of these constants is a multiple of
         * the other.
         */
        lcm_align = lcm(PAGE_SIZE, PCPU_BITMAP_BLOCK_SIZE);
        region_size = ALIGN(start_offset + map_size, lcm_align);

        /* allocate chunk */
        alloc_size = sizeof(struct pcpu_chunk) +
                BITS_TO_LONGS(region_size >> PAGE_SHIFT);
        chunk = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
        if (!chunk)
                panic("%s: Failed to allocate %zu bytes\n", __func__,
                      alloc_size);

        INIT_LIST_HEAD(&chunk->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;
        region_bits = pcpu_chunk_map_bits(chunk);

        alloc_size = BITS_TO_LONGS(region_bits) * sizeof(chunk->alloc_map[0]);
        chunk->alloc_map = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
        if (!chunk->alloc_map)
                panic("%s: Failed to allocate %zu bytes\n", __func__,
                      alloc_size);

        alloc_size =
                BITS_TO_LONGS(region_bits + 1) * sizeof(chunk->bound_map[0]);
        chunk->bound_map = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
        if (!chunk->bound_map)
                panic("%s: Failed to allocate %zu bytes\n", __func__,
                      alloc_size);

        alloc_size = pcpu_chunk_nr_blocks(chunk) * sizeof(chunk->md_blocks[0]);
        chunk->md_blocks = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
        if (!chunk->md_blocks)
                panic("%s: Failed to allocate %zu bytes\n", __func__,
                      alloc_size);

        pcpu_init_md_blocks(chunk);

        /* 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_bits = map_size / PCPU_MIN_ALLOC_SIZE;
        chunk->free_bytes = map_size;

        if (chunk->start_offset) {
                /* hide the beginning of the bitmap */
                offset_bits = chunk->start_offset / PCPU_MIN_ALLOC_SIZE;
                bitmap_set(chunk->alloc_map, 0, offset_bits);
                set_bit(0, chunk->bound_map);
                set_bit(offset_bits, chunk->bound_map);

                chunk->first_bit = offset_bits;

                pcpu_block_update_hint_alloc(chunk, 0, offset_bits);
        }

        if (chunk->end_offset) {
                /* hide the end of the bitmap */
                offset_bits = chunk->end_offset / PCPU_MIN_ALLOC_SIZE;
                bitmap_set(chunk->alloc_map,
                           pcpu_chunk_map_bits(chunk) - offset_bits,
                           offset_bits);
                set_bit((start_offset + map_size) / PCPU_MIN_ALLOC_SIZE,
                        chunk->bound_map);
                set_bit(region_bits, chunk->bound_map);

                pcpu_block_update_hint_alloc(chunk, pcpu_chunk_map_bits(chunk)
                                             - offset_bits, offset_bits);
        }

        return chunk;
}

static struct pcpu_chunk *pcpu_alloc_chunk(gfp_t gfp)
{
        struct pcpu_chunk *chunk;
        int region_bits;

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

        INIT_LIST_HEAD(&chunk->list);
        chunk->nr_pages = pcpu_unit_pages;
        region_bits = pcpu_chunk_map_bits(chunk);

        chunk->alloc_map = pcpu_mem_zalloc(BITS_TO_LONGS(region_bits) *
                                           sizeof(chunk->alloc_map[0]), gfp);
        if (!chunk->alloc_map)
                goto alloc_map_fail;

        chunk->bound_map = pcpu_mem_zalloc(BITS_TO_LONGS(region_bits + 1) *
                                           sizeof(chunk->bound_map[0]), gfp);
        if (!chunk->bound_map)
                goto bound_map_fail;

        chunk->md_blocks = pcpu_mem_zalloc(pcpu_chunk_nr_blocks(chunk) *
                                           sizeof(chunk->md_blocks[0]), gfp);
        if (!chunk->md_blocks)
                goto md_blocks_fail;

        pcpu_init_md_blocks(chunk);

        /* init metadata */
        chunk->contig_bits = region_bits;
        chunk->free_bytes = chunk->nr_pages * PAGE_SIZE;

        return chunk;

md_blocks_fail:
        pcpu_mem_free(chunk->bound_map);
bound_map_fail:
        pcpu_mem_free(chunk->alloc_map);
alloc_map_fail:
        pcpu_mem_free(chunk);

        return NULL;
}

static void pcpu_free_chunk(struct pcpu_chunk *chunk)
{
        if (!chunk)
                return;
        pcpu_mem_free(chunk->md_blocks);
        pcpu_mem_free(chunk->bound_map);
        pcpu_mem_free(chunk->alloc_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.
 *
 * If this is @for_alloc, do not increment pcpu_nr_empty_pop_pages because it
 * is to serve an allocation in that area.
 */
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;
        pcpu_nr_populated += nr;

        pcpu_update_empty_pages(chunk, 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;
        pcpu_nr_populated -= nr;

        pcpu_update_empty_pages(chunk, -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 page_start, int page_end, gfp_t gfp);
static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
                                  int page_start, int page_end);
static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp);
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. If @gfp has __GFP_NOWARN
 * then no warning will be triggered on invalid or failed allocation
 * requests.
 *
 * 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)
{
        /* whitelisted flags that can be passed to the backing allocators */
        gfp_t pcpu_gfp = gfp & (GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN);
        bool is_atomic = (gfp & GFP_KERNEL) != GFP_KERNEL;
        bool do_warn = !(gfp & __GFP_NOWARN);
        static int warn_limit = 10;
        struct pcpu_chunk *chunk, *next;
        const char *err;
        int slot, off, cpu, ret;
        unsigned long flags;
        void __percpu *ptr;
        size_t bits, bit_align;

        /*
         * There is now a minimum allocation size of PCPU_MIN_ALLOC_SIZE,
         * therefore alignment must be a minimum of that many bytes.
         * An allocation may have internal fragmentation from rounding up
         * of up to PCPU_MIN_ALLOC_SIZE - 1 bytes.
         */
        if (unlikely(align < PCPU_MIN_ALLOC_SIZE))
                align = PCPU_MIN_ALLOC_SIZE;

        size = ALIGN(size, PCPU_MIN_ALLOC_SIZE);
        bits = size >> PCPU_MIN_ALLOC_SHIFT;
        bit_align = align >> PCPU_MIN_ALLOC_SHIFT;

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

        if (!is_atomic) {
                /*
                 * pcpu_balance_workfn() allocates memory under this mutex,
                 * and it may wait for memory reclaim. Allow current task
                 * to become OOM victim, in case of memory pressure.
                 */
                if (gfp & __GFP_NOFAIL)
                        mutex_lock(&pcpu_alloc_mutex);
                else if (mutex_lock_killable(&pcpu_alloc_mutex))
                        return NULL;
        }

        spin_lock_irqsave(&pcpu_lock, flags);

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

                off = pcpu_find_block_fit(chunk, bits, bit_align, is_atomic);
                if (off < 0) {
                        err = "alloc from reserved chunk failed";
                        goto fail_unlock;
                }

                off = pcpu_alloc_area(chunk, bits, bit_align, off);
                if (off >= 0)
                        goto area_found;

                err = "alloc from reserved chunk failed";
                goto fail_unlock;
        }

restart:
        /* search through normal chunks */
        for (slot = pcpu_size_to_slot(size); slot < pcpu_nr_slots; slot++) {
                list_for_each_entry_safe(chunk, next, &pcpu_slot[slot], list) {
                        off = pcpu_find_block_fit(chunk, bits, bit_align,
                                                  is_atomic);
                        if (off < 0) {
                                if (slot < PCPU_SLOT_FAIL_THRESHOLD)
                                        pcpu_chunk_move(chunk, 0);
                                continue;
                        }

                        off = pcpu_alloc_area(chunk, bits, bit_align, off);
                        if (off >= 0)
                                goto area_found;

                }
        }

        spin_unlock_irqrestore(&pcpu_lock, flags);

        /*
         * No space left.  Create a new chunk.  We don't want multiple
         * tasks to create chunks simultaneously.  Serialize and create iff
         * there's still no empty chunk after grabbing the mutex.
         */
        if (is_atomic) {
                err = "atomic alloc failed, no space left";
                goto fail;
        }

        if (list_empty(&pcpu_slot[pcpu_nr_slots - 1])) {
                chunk = pcpu_create_chunk(pcpu_gfp);
                if (!chunk) {
                        err = "failed to allocate new chunk";
                        goto fail;
                }

                spin_lock_irqsave(&pcpu_lock, flags);
                pcpu_chunk_relocate(chunk, -1);
        } else {
                spin_lock_irqsave(&pcpu_lock, flags);
        }

        goto restart;

area_found:
        pcpu_stats_area_alloc(chunk, size);
        spin_unlock_irqrestore(&pcpu_lock, flags);

        /* populate if not all pages are already there */
        if (!is_atomic) {
                int page_start, page_end, rs, re;

                page_start = PFN_DOWN(off);
                page_end = PFN_UP(off + size);

                pcpu_for_each_unpop_region(chunk->populated, rs, re,
                                           page_start, page_end) {
                        WARN_ON(chunk->immutable);

                        ret = pcpu_populate_chunk(chunk, rs, re, pcpu_gfp);

                        spin_lock_irqsave(&pcpu_lock, flags);
                        if (ret) {
                                pcpu_free_area(chunk, off);
                                err = "failed to populate";
                                goto fail_unlock;
                        }
                        pcpu_chunk_populated(chunk, rs, re);
                        spin_unlock_irqrestore(&pcpu_lock, flags);
                }

                mutex_unlock(&pcpu_alloc_mutex);
        }

        if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW)
                pcpu_schedule_balance_work();

        /* clear the areas and return address relative to base address */
        for_each_possible_cpu(cpu)
                memset((void *)pcpu_chunk_addr(chunk, cpu, 0) + off, 0, size);

        ptr = __addr_to_pcpu_ptr(chunk->base_addr + off);
        kmemleak_alloc_percpu(ptr, size, gfp);

        trace_percpu_alloc_percpu(reserved, is_atomic, size, align,
                        chunk->base_addr, off, ptr);

        return ptr;

fail_unlock:
        spin_unlock_irqrestore(&pcpu_lock, flags);
fail:
        trace_percpu_alloc_percpu_fail(reserved, is_atomic, size, align);

        if (!is_atomic && do_warn && warn_limit) {
                pr_warn("allocation failed, size=%zu align=%zu atomic=%d, %s\n",
                        size, align, is_atomic, err);
                dump_stack();
                if (!--warn_limit)
                        pr_info("limit reached, disable warning\n");
        }
        if (is_atomic) {
                /* see the flag handling in pcpu_blance_workfn() */
                pcpu_atomic_alloc_failed = true;
                pcpu_schedule_balance_work();
        } else {
                mutex_unlock(&pcpu_alloc_mutex);
        }
        return NULL;
}

/**
 * __alloc_percpu_gfp - allocate dynamic percpu area
 * @size: size of area to allocate in bytes
 * @align: alignment of area (max PAGE_SIZE)
 * @gfp: allocation flags
 *
 * Allocate zero-filled percpu area of @size bytes aligned at @align.  If
 * @gfp doesn't contain %GFP_KERNEL, the allocation doesn't block and can
 * be called from any context but is a lot more likely to fail. If @gfp
 * has __GFP_NOWARN then no warning will be triggered on invalid or failed
 * allocation requests.
 *
 * RETURNS:
 * Percpu pointer to the allocated area on success, NULL on failure.
 */
void __percpu *__alloc_percpu_gfp(size_t size, size_t align, gfp_t gfp)
{
        return pcpu_alloc(size, align, false, gfp);
}
EXPORT_SYMBOL_GPL(__alloc_percpu_gfp);

/**
 * __alloc_percpu - allocate dynamic percpu area
 * @size: size of area to allocate in bytes
 * @align: alignment of area (max PAGE_SIZE)
 *
 * Equivalent to __alloc_percpu_gfp(size, align, %GFP_KERNEL).
 */
void __percpu *__alloc_percpu(size_t size, size_t align)
{
        return pcpu_alloc(size, align, false, GFP_KERNEL);
}
EXPORT_SYMBOL_GPL(__alloc_percpu);

/**
 * __alloc_reserved_percpu - allocate reserved percpu area
 * @size: size of area to allocate in bytes
 * @align: alignment of area (max PAGE_SIZE)
 *
 * Allocate zero-filled percpu area of @size bytes aligned at @align
 * from reserved percpu area if arch has set it up; otherwise,
 * allocation is served from the same dynamic area.  Might sleep.
 * Might trigger writeouts.
 *
 * CONTEXT:
 * Does GFP_KERNEL allocation.
 *
 * RETURNS:
 * Percpu pointer to the allocated area on success, NULL on failure.
 */
void __percpu *__alloc_reserved_percpu(size_t size, size_t align)
{
        return pcpu_alloc(size, align, true, GFP_KERNEL);
}

/**
 * pcpu_balance_workfn - manage the amount of free chunks and populated pages
 * @work: unused
 *
 * Reclaim all fully free chunks except for the first one.  This is also
 * responsible for maintaining the pool of empty populated pages.  However,
 * it is possible that this is called when physical memory is scarce causing
 * OOM killer to be triggered.  We should avoid doing so until an actual
 * allocation causes the failure as it is possible that requests can be
 * serviced from already backed regions.
 */
static void pcpu_balance_workfn(struct work_struct *work)
{
        /* gfp flags passed to underlying allocators */
        const gfp_t gfp = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
        LIST_HEAD(to_free);
        struct list_head *free_head = &pcpu_slot[pcpu_nr_slots - 1];
        struct pcpu_chunk *chunk, *next;
        int slot, nr_to_pop, ret;

        /*
         * There's no reason to keep around multiple unused chunks and VM
         * areas can be scarce.  Destroy all free chunks except for one.
         */
        mutex_lock(&pcpu_alloc_mutex);
        spin_lock_irq(&pcpu_lock);

        list_for_each_entry_safe(chunk, next, free_head, list) {
                WARN_ON(chunk->immutable);

                /* spare the first one */
                if (chunk == list_first_entry(free_head, struct pcpu_chunk, list))
                        continue;

                list_move(&chunk->list, &to_free);
        }

        spin_unlock_irq(&pcpu_lock);

        list_for_each_entry_safe(chunk, next, &to_free, list) {
                int rs, re;

                pcpu_for_each_pop_region(chunk->populated, rs, re, 0,
                                         chunk->nr_pages) {
                        pcpu_depopulate_chunk(chunk, rs, re);
                        spin_lock_irq(&pcpu_lock);
                        pcpu_chunk_depopulated(chunk, rs, re);
                        spin_unlock_irq(&pcpu_lock);
                }
                pcpu_destroy_chunk(chunk);
                cond_resched();
        }

        /*
         * Ensure there are certain number of free populated pages for
         * atomic allocs.  Fill up from the most packed so that atomic
         * allocs don't increase fragmentation.  If atomic allocation
         * failed previously, always populate the maximum amount.  This
         * should prevent atomic allocs larger than PAGE_SIZE from keeping
         * failing indefinitely; however, large atomic allocs are not
         * something we support properly and can be highly unreliable and
         * inefficient.
         */
retry_pop:
        if (pcpu_atomic_alloc_failed) {
                nr_to_pop = PCPU_EMPTY_POP_PAGES_HIGH;
                /* best effort anyway, don't worry about synchronization */
                pcpu_atomic_alloc_failed = false;
        } else {
                nr_to_pop = clamp(PCPU_EMPTY_POP_PAGES_HIGH -
                                  pcpu_nr_empty_pop_pages,
                                  0, PCPU_EMPTY_POP_PAGES_HIGH);
        }

        for (slot = pcpu_size_to_slot(PAGE_SIZE); slot < pcpu_nr_slots; slot++) {
                int nr_unpop = 0, rs, re;

                if (!nr_to_pop)
                        break;

                spin_lock_irq(&pcpu_lock);
                list_for_each_entry(chunk, &pcpu_slot[slot], list) {
                        nr_unpop = chunk->nr_pages - chunk->nr_populated;
                        if (nr_unpop)
                                break;
                }
                spin_unlock_irq(&pcpu_lock);

                if (!nr_unpop)
                        continue;

                /* @chunk can't go away while pcpu_alloc_mutex is held */
                pcpu_for_each_unpop_region(chunk->populated, rs, re, 0,
                                           chunk->nr_pages) {
                        int nr = min(re - rs, nr_to_pop);

                        ret = pcpu_populate_chunk(chunk, rs, rs + nr, gfp);
                        if (!ret) {
                                nr_to_pop -= nr;
                                spin_lock_irq(&pcpu_lock);
                                pcpu_chunk_populated(chunk, rs, rs + nr);
                                spin_unlock_irq(&pcpu_lock);
                        } else {
                                nr_to_pop = 0;
                        }

                        if (!nr_to_pop)
                                break;
                }
        }

        if (nr_to_pop) {
                /* ran out of chunks to populate, create a new one and retry */
                chunk = pcpu_create_chunk(gfp);
                if (chunk) {
                        spin_lock_irq(&pcpu_lock);
                        pcpu_chunk_relocate(chunk, -1);
                        spin_unlock_irq(&pcpu_lock);
                        goto retry_pop;
                }
        }

        mutex_unlock(&pcpu_alloc_mutex);
}

/**
 * free_percpu - free percpu area
 * @ptr: pointer to area to free
 *
 * Free percpu area @ptr.
 *
 * CONTEXT:
 * Can be called from atomic context.
 */
void free_percpu(void __percpu *ptr)
{
        void *addr;
        struct pcpu_chunk *chunk;
        unsigned long flags;
        int off;

        if (!ptr)
                return;

        kmemleak_free_percpu(ptr);

        addr = __pcpu_ptr_to_addr(ptr);

        spin_lock_irqsave(&pcpu_lock, flags);

        chunk = pcpu_chunk_addr_search(addr);
        off = addr - chunk->base_addr;

        pcpu_free_area(chunk, off);

        /* if there are more than one fully free chunks, wake up grim reaper */
        if (chunk->free_bytes == pcpu_unit_size) {
                struct pcpu_chunk *pos;

                list_for_each_entry(pos, &pcpu_slot[pcpu_nr_slots - 1], list)
                        if (pos != chunk) {
                                pcpu_schedule_balance_work();
                                break;
                        }
        }

        trace_percpu_free_percpu(chunk->base_addr, off, ptr);

        spin_unlock_irqrestore(&pcpu_lock, flags);
}
EXPORT_SYMBOL_GPL(free_percpu);

bool __is_kernel_percpu_address(unsigned long addr, unsigned long *can_addr)
{
#ifdef CONFIG_SMP
        const size_t static_size = __per_cpu_end - __per_cpu_start;
        void __percpu *base = __addr_to_pcpu_ptr(pcpu_base_addr);
        unsigned int cpu;

        for_each_possible_cpu(cpu) {
                void *start = per_cpu_ptr(base, cpu);
                void *va = (void *)addr;

                if (va >= start && va < start + static_size) {
                        if (can_addr) {
                                *can_addr = (unsigned long) (va - start);
                                *can_addr += (unsigned long)
                                        per_cpu_ptr(base, get_boot_cpu_id());
                        }
                        return true;
                }
        }
#endif
        /* on UP, can't distinguish from other static vars, always false */
        return false;
}

/**
 * is_kernel_percpu_address - test whether address is from static percpu area
 * @addr: address to test
 *
 * Test whether @addr belongs to in-kernel static percpu area.  Module
 * static percpu areas are not considered.  For those, use
 * is_module_percpu_address().
 *
 * RETURNS:
 * %true if @addr is from in-kernel static percpu area, %false otherwise.
 */
bool is_kernel_percpu_address(unsigned long addr)
{
        return __is_kernel_percpu_address(addr, NULL);
}

/**
 * per_cpu_ptr_to_phys - convert translated percpu address to physical address
 * @addr: the address to be converted to physical address
 *
 * Given @addr which is dereferenceable address obtained via one of
 * percpu access macros, this function translates it into its physical
 * address.  The caller is responsible for ensuring @addr stays valid
 * until this function finishes.
 *
 * percpu allocator has special setup for the first chunk, which currently
 * supports either embedding in linear address space or vmalloc mapping,
 * and, from the second one, the backing allocator (currently either vm or
 * km) provides translation.
 *
 * The addr can be translated simply without checking if it falls into the
 * first chunk. But the current code reflects better how percpu allocator
 * actually works, and the verification can discover both bugs in percpu
 * allocator itself and per_cpu_ptr_to_phys() callers. So we keep current
 * code.
 *
 * RETURNS:
 * The physical address for @addr.
 */
phys_addr_t per_cpu_ptr_to_phys(void *addr)
{
        void __percpu *base = __addr_to_pcpu_ptr(pcpu_base_addr);
        bool in_first_chunk = false;
        unsigned long first_low, first_high;
        unsigned int cpu;

        /*
         * The following test on unit_low/high isn't strictly
         * necessary but will speed up lookups of addresses which
         * aren't in the first chunk.
         *
         * The address check is against full chunk sizes.  pcpu_base_addr
         * points to the beginning of the first chunk including the
         * static region.  Assumes good intent as the first chunk may
         * not be full (ie. < pcpu_unit_pages in size).
         */
        first_low = (unsigned long)pcpu_base_addr +
                    pcpu_unit_page_offset(pcpu_low_unit_cpu, 0);
        first_high = (unsigned long)pcpu_base_addr +
                     pcpu_unit_page_offset(pcpu_high_unit_cpu, pcpu_unit_pages);
        if ((unsigned long)addr >= first_low &&
            (unsigned long)addr < first_high) {
                for_each_possible_cpu(cpu) {
                        void *start = per_cpu_ptr(base, cpu);

                        if (addr >= start && addr < start + pcpu_unit_size) {
                                in_first_chunk = true;
                                break;
                        }
                }
        }

        if (in_first_chunk) {
                if (!is_vmalloc_addr(addr))
                        return __pa(addr);
                else
                        return page_to_phys(vmalloc_to_page(addr)) +
                               offset_in_page(addr);
        } else
                return page_to_phys(pcpu_addr_to_page(addr)) +
                       offset_in_page(addr);
}

/**
 * pcpu_alloc_alloc_info - allocate percpu allocation info
 * @nr_groups: the number of groups
 * @nr_units: the number of units
 *
 * Allocate ai which is large enough for @nr_groups groups containing
 * @nr_units units.  The returned ai's groups[0].cpu_map points to the
 * cpu_map array which is long enough for @nr_units and filled with
 * NR_CPUS.  It's the caller's responsibility to initialize cpu_map
 * pointer of other groups.
 *
 * RETURNS:
 * Pointer to the allocated pcpu_alloc_info on success, NULL on
 * failure.
 */
struct pcpu_alloc_info * __init pcpu_alloc_alloc_info(int nr_groups,
                                                      int nr_units)
{
        struct pcpu_alloc_info *ai;
        size_t base_size, ai_size;
        void *ptr;
        int unit;

        base_size = ALIGN(sizeof(*ai) + nr_groups * sizeof(ai->groups[0]),
                          __alignof__(ai->groups[0].cpu_map[0]));
        ai_size = base_size + nr_units * sizeof(ai->groups[0].cpu_map[0]);

        ptr = memblock_alloc(PFN_ALIGN(ai_size), PAGE_SIZE);
        if (!ptr)
                return NULL;
        ai = ptr;
        ptr += base_size;

        ai->groups[0].cpu_map = ptr;

        for (unit = 0; unit < nr_units; unit++)
                ai->groups[0].cpu_map[unit] = NR_CPUS;

        ai->nr_groups = nr_groups;
        ai->__ai_size = PFN_ALIGN(ai_size);

        return ai;
}

/**
 * pcpu_free_alloc_info - free percpu allocation info
 * @ai: pcpu_alloc_info to free
 *
 * Free @ai which was allocated by pcpu_alloc_alloc_info().
 */
void __init pcpu_free_alloc_info(struct pcpu_alloc_info *ai)
{
        memblock_free_early(__pa(ai), ai->__ai_size);
}

/**
 * pcpu_dump_alloc_info - print out information about pcpu_alloc_info
 * @lvl: loglevel
 * @ai: allocation info to dump
 *
 * Print out information about @ai using loglevel @lvl.
 */
static void pcpu_dump_alloc_info(const char *lvl,
                                 const struct pcpu_alloc_info *ai)
{
        int group_width = 1, cpu_width = 1, width;
        char empty_str[] = "--------";
        int alloc = 0, alloc_end = 0;
        int group, v;
        int upa, apl;   /* units per alloc, allocs per line */

        v = ai->nr_groups;
        while (v /= 10)
                group_width++;

        v = num_possible_cpus();
        while (v /= 10)
                cpu_width++;
        empty_str[min_t(int, cpu_width, sizeof(empty_str) - 1)] = '\0';

        upa = ai->alloc_size / ai->unit_size;
        width = upa * (cpu_width + 1) + group_width + 3;
        apl = rounddown_pow_of_two(max(60 / width, 1));

        printk("%spcpu-alloc: s%zu r%zu d%zu u%zu alloc=%zu*%zu",
               lvl, ai->static_size, ai->reserved_size, ai->dyn_size,
               ai->unit_size, ai->alloc_size / ai->atom_size, ai->atom_size);

        for (group = 0; group < ai->nr_groups; group++) {
                const struct pcpu_group_info *gi = &ai->groups[group];
                int unit = 0, unit_end = 0;

                BUG_ON(gi->nr_units % upa);
                for (alloc_end += gi->nr_units / upa;
                     alloc < alloc_end; alloc++) {
                        if (!(alloc % apl)) {
                                pr_cont("\n");
                                printk("%spcpu-alloc: ", lvl);
                        }
                        pr_cont("[%0*d] ", group_width, group);

                        for (unit_end += upa; unit < unit_end; unit++)
                                if (gi->cpu_map[unit] != NR_CPUS)
                                        pr_cont("%0*d ",
                                                cpu_width, gi->cpu_map[unit]);
                                else
                                        pr_cont("%s ", empty_str);
                }
        }
        pr_cont("\n");
}

/**
 * pcpu_setup_first_chunk - initialize the first percpu chunk
 * @ai: pcpu_alloc_info describing how to percpu area is shaped
 * @base_addr: mapped address
 *
 * Initialize the first percpu chunk which contains the kernel static
 * perpcu area.  This function is to be called from arch percpu area
 * setup path.
 *
 * @ai contains all information necessary to initialize the first
 * chunk and prime the dynamic percpu allocator.
 *
 * @ai->static_size is the size of static percpu area.
 *
 * @ai->reserved_size, if non-zero, specifies the amount of bytes to
 * reserve after the static area in the first chunk.  This reserves
 * the first chunk such that it's available only through reserved
 * percpu allocation.  This is primarily used to serve module percpu
 * static areas on architectures where the addressing model has
 * limited offset range for symbol relocations to guarantee module
 * percpu symbols fall inside the relocatable range.
 *
 * @ai->dyn_size determines the number of bytes available for dynamic
 * allocation in the first chunk.  The area between @ai->static_size +
 * @ai->reserved_size + @ai->dyn_size and @ai->unit_size is unused.
 *
 * @ai->unit_size specifies unit size and must be aligned to PAGE_SIZE
 * and equal to or larger than @ai->static_size + @ai->reserved_size +
 * @ai->dyn_size.
 *
 * @ai->atom_size is the allocation atom size and used as alignment
 * for vm areas.
 *
 * @ai->alloc_size is the allocation size and always multiple of
 * @ai->atom_size.  This is larger than @ai->atom_size if
 * @ai->unit_size is larger than @ai->atom_size.
 *
 * @ai->nr_groups and @ai->groups describe virtual memory layout of
 * percpu areas.  Units which should be colocated are put into the
 * same group.  Dynamic VM areas will be allocated according to these
 * groupings.  If @ai->nr_groups is zero, a single group containing
 * all units is assumed.
 *
 * The caller should have mapped the first chunk at @base_addr and
 * copied static data to each unit.
 *
 * The first chunk will always contain a static and a dynamic region.
 * However, the static region is not managed by any chunk.  If the first
 * chunk also contains a reserved region, it is served by two chunks -
 * one for the reserved region and one for the dynamic region.  They
 * share the same vm, but use offset regions in the area allocation map.
 * The chunk serving the dynamic region is circulated in the chunk slots
 * and available for dynamic allocation like any other chunk.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
                                  void *base_addr)
{
        size_t size_sum = ai->static_size + ai->reserved_size + ai->dyn_size;
        size_t static_size, dyn_size;
        struct pcpu_chunk *chunk;
        unsigned long *group_offsets;
        size_t *group_sizes;
        unsigned long *unit_off;
        unsigned int cpu;
        int *unit_map;
        int group, unit, i;
        int map_size;
        unsigned long tmp_addr;
        size_t alloc_size;

#define PCPU_SETUP_BUG_ON(cond) do {                                    \
        if (unlikely(cond)) {                                           \
                pr_emerg("failed to initialize, %s\n", #cond);          \
                pr_emerg("cpu_possible_mask=%*pb\n",                    \
                         cpumask_pr_args(cpu_possible_mask));           \
                pcpu_dump_alloc_info(KERN_EMERG, ai);                   \
                BUG();                                                  \
        }                                                               \
} while (0)

        /* sanity checks */
        PCPU_SETUP_BUG_ON(ai->nr_groups <= 0);
#ifdef CONFIG_SMP
        PCPU_SETUP_BUG_ON(!ai->static_size);
        PCPU_SETUP_BUG_ON(offset_in_page(__per_cpu_start));
#endif
        PCPU_SETUP_BUG_ON(!base_addr);
        PCPU_SETUP_BUG_ON(offset_in_page(base_addr));
        PCPU_SETUP_BUG_ON(ai->unit_size < size_sum);
        PCPU_SETUP_BUG_ON(offset_in_page(ai->unit_size));
        PCPU_SETUP_BUG_ON(ai->unit_size < PCPU_MIN_UNIT_SIZE);
        PCPU_SETUP_BUG_ON(!IS_ALIGNED(ai->unit_size, PCPU_BITMAP_BLOCK_SIZE));
        PCPU_SETUP_BUG_ON(ai->dyn_size < PERCPU_DYNAMIC_EARLY_SIZE);
        PCPU_SETUP_BUG_ON(!ai->dyn_size);
        PCPU_SETUP_BUG_ON(!IS_ALIGNED(ai->reserved_size, PCPU_MIN_ALLOC_SIZE));
        PCPU_SETUP_BUG_ON(!(IS_ALIGNED(PCPU_BITMAP_BLOCK_SIZE, PAGE_SIZE) ||
                            IS_ALIGNED(PAGE_SIZE, PCPU_BITMAP_BLOCK_SIZE)));
        PCPU_SETUP_BUG_ON(pcpu_verify_alloc_info(ai) < 0);

        /* process group information and build config tables accordingly */
        alloc_size = ai->nr_groups * sizeof(group_offsets[0]);
        group_offsets = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
        if (!group_offsets)
                panic("%s: Failed to allocate %zu bytes\n", __func__,
                      alloc_size);

        alloc_size = ai->nr_groups * sizeof(group_sizes[0]);
        group_sizes = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
        if (!group_sizes)
                panic("%s: Failed to allocate %zu bytes\n", __func__,
                      alloc_size);

        alloc_size = nr_cpu_ids * sizeof(unit_map[0]);
        unit_map = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
        if (!unit_map)
                panic("%s: Failed to allocate %zu bytes\n", __func__,
                      alloc_size);

        alloc_size = nr_cpu_ids * sizeof(unit_off[0]);
        unit_off = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
        if (!unit_off)
                panic("%s: Failed to allocate %zu bytes\n", __func__,
                      alloc_size);

        for (cpu = 0; cpu < nr_cpu_ids; cpu++)
                unit_map[cpu] = UINT_MAX;

        pcpu_low_unit_cpu = NR_CPUS;
        pcpu_high_unit_cpu = NR_CPUS;

        for (group = 0, unit = 0; group < ai->nr_groups; group++, unit += i) {
                const struct pcpu_group_info *gi = &ai->groups[group];

                group_offsets[group] = gi->base_offset;
                group_sizes[group] = gi->nr_units * ai->unit_size;

                for (i = 0; i < gi->nr_units; i++) {
                        cpu = gi->cpu_map[i];
                        if (cpu == NR_CPUS)
                                continue;

                        PCPU_SETUP_BUG_ON(cpu >= nr_cpu_ids);
                        PCPU_SETUP_BUG_ON(!cpu_possible(cpu));
                        PCPU_SETUP_BUG_ON(unit_map[cpu] != UINT_MAX);

                        unit_map[cpu] = unit + i;
                        unit_off[cpu] = gi->base_offset + i * ai->unit_size;

                        /* determine low/high unit_cpu */
                        if (pcpu_low_unit_cpu == NR_CPUS ||
                            unit_off[cpu] < unit_off[pcpu_low_unit_cpu])
                                pcpu_low_unit_cpu = cpu;
                        if (pcpu_high_unit_cpu == NR_CPUS ||
                            unit_off[cpu] > unit_off[pcpu_high_unit_cpu])
                                pcpu_high_unit_cpu = cpu;
                }
        }
        pcpu_nr_units = unit;

        for_each_possible_cpu(cpu)
                PCPU_SETUP_BUG_ON(unit_map[cpu] == UINT_MAX);

        /* we're done parsing the input, undefine BUG macro and dump config */
#undef PCPU_SETUP_BUG_ON
        pcpu_dump_alloc_info(KERN_DEBUG, ai);

        pcpu_nr_groups = ai->nr_groups;
        pcpu_group_offsets = group_offsets;
        pcpu_group_sizes = group_sizes;
        pcpu_unit_map = unit_map;
        pcpu_unit_offsets = unit_off;

        /* determine basic parameters */
        pcpu_unit_pages = ai->unit_size >> PAGE_SHIFT;
        pcpu_unit_size = pcpu_unit_pages << PAGE_SHIFT;
        pcpu_atom_size = ai->atom_size;
        pcpu_chunk_struct_size = sizeof(struct pcpu_chunk) +
                BITS_TO_LONGS(pcpu_unit_pages) * sizeof(unsigned long);

        pcpu_stats_save_ai(ai);

        /*
         * Allocate chunk slots.  The additional last slot is for
         * empty chunks.
         */
        pcpu_nr_slots = __pcpu_size_to_slot(pcpu_unit_size) + 2;
        pcpu_slot = memblock_alloc(pcpu_nr_slots * sizeof(pcpu_slot[0]),
                                   SMP_CACHE_BYTES);
        if (!pcpu_slot)
                panic("%s: Failed to allocate %zu bytes\n", __func__,
                      pcpu_nr_slots * sizeof(pcpu_slot[0]));
        for (i = 0; i < pcpu_nr_slots; i++)
                INIT_LIST_HEAD(&pcpu_slot[i]);

        /*
         * The end of the static region needs to be aligned with the
         * minimum allocation size as this offsets the reserved and
         * dynamic region.  The first chunk ends page aligned by
         * expanding the dynamic region, therefore the dynamic region
         * can be shrunk to compensate while still staying above the
         * configured sizes.
         */
        static_size = ALIGN(ai->static_size, PCPU_MIN_ALLOC_SIZE);
        dyn_size = ai->dyn_size - (static_size - ai->static_size);

        /*
         * Initialize first chunk.
         * If the reserved_size is non-zero, this initializes the reserved
         * chunk.  If the reserved_size is zero, the reserved chunk is NULL
         * and the dynamic region is initialized here.  The first chunk,
         * pcpu_first_chunk, will always point to the chunk that serves
         * the dynamic region.
         */
        tmp_addr = (unsigned long)base_addr + static_size;
        map_size = ai->reserved_size ?: dyn_size;
        chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);

        /* init dynamic chunk if necessary */
        if (ai->reserved_size) {
                pcpu_reserved_chunk = chunk;

                tmp_addr = (unsigned long)base_addr + static_size +
                           ai->reserved_size;
                map_size = dyn_size;
                chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);
        }

        /* link the first chunk in */
        pcpu_first_chunk = chunk;
        pcpu_nr_empty_pop_pages = pcpu_first_chunk->nr_empty_pop_pages;
        pcpu_chunk_relocate(pcpu_first_chunk, -1);

        /* include all regions of the first chunk */
        pcpu_nr_populated += PFN_DOWN(size_sum);

        pcpu_stats_chunk_alloc();
        trace_percpu_create_chunk(base_addr);

        /* we're done */
        pcpu_base_addr = base_addr;
        return 0;
}

#ifdef CONFIG_SMP

const char * const pcpu_fc_names[PCPU_FC_NR] __initconst = {
        [PCPU_FC_AUTO]  = "auto",
        [PCPU_FC_EMBED] = "embed",
        [PCPU_FC_PAGE]  = "page",
};

enum pcpu_fc pcpu_chosen_fc __initdata = PCPU_FC_AUTO;

static int __init percpu_alloc_setup(char *str)
{
        if (!str)
                return -EINVAL;

        if (0)
                /* nada */;
#ifdef CONFIG_NEED_PER_CPU_EMBED_FIRST_CHUNK
        else if (!strcmp(str, "embed"))
                pcpu_chosen_fc = PCPU_FC_EMBED;
#endif
#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
        else if (!strcmp(str, "page"))
                pcpu_chosen_fc = PCPU_FC_PAGE;
#endif
        else
                pr_warn("unknown allocator %s specified\n", str);

        return 0;
}
early_param("percpu_alloc", percpu_alloc_setup);

/*
 * pcpu_embed_first_chunk() is used by the generic percpu setup.
 * Build it if needed by the arch config or the generic setup is going
 * to be used.
 */
#if defined(CONFIG_NEED_PER_CPU_EMBED_FIRST_CHUNK) || \
        !defined(CONFIG_HAVE_SETUP_PER_CPU_AREA)
#define BUILD_EMBED_FIRST_CHUNK
#endif

/* build pcpu_page_first_chunk() iff needed by the arch config */
#if defined(CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK)
#define BUILD_PAGE_FIRST_CHUNK
#endif

/* pcpu_build_alloc_info() is used by both embed and page first chunk */
#if defined(BUILD_EMBED_FIRST_CHUNK) || defined(BUILD_PAGE_FIRST_CHUNK)
/**
 * pcpu_build_alloc_info - build alloc_info considering distances between CPUs
 * @reserved_size: the size of reserved percpu area in bytes
 * @dyn_size: minimum free size for dynamic allocation in bytes
 * @atom_size: allocation atom size
 * @cpu_distance_fn: callback to determine distance between cpus, optional
 *
 * This function determines grouping of units, their mappings to cpus
 * and other parameters considering needed percpu size, allocation
 * atom size and distances between CPUs.
 *
 * Groups are always multiples of atom size and CPUs which are of
 * LOCAL_DISTANCE both ways are grouped together and share space for
 * units in the same group.  The returned configuration is guaranteed
 * to have CPUs on different nodes on different groups and >=75% usage
 * of allocated virtual address space.
 *
 * RETURNS:
 * On success, pointer to the new allocation_info is returned.  On
 * failure, ERR_PTR value is returned.
 */
static struct pcpu_alloc_info * __init pcpu_build_alloc_info(
                                size_t reserved_size, size_t dyn_size,
                                size_t atom_size,
                                pcpu_fc_cpu_distance_fn_t cpu_distance_fn)
{
        static int group_map[NR_CPUS] __initdata;
        static int group_cnt[NR_CPUS] __initdata;
        const size_t static_size = __per_cpu_end - __per_cpu_start;
        int nr_groups = 1, nr_units = 0;
        size_t size_sum, min_unit_size, alloc_size;
        int upa, max_upa, uninitialized_var(best_upa);  /* units_per_alloc */
        int last_allocs, group, unit;
        unsigned int cpu, tcpu;
        struct pcpu_alloc_info *ai;
        unsigned int *cpu_map;

        /* this function may be called multiple times */
        memset(group_map, 0, sizeof(group_map));
        memset(group_cnt, 0, sizeof(group_cnt));

        /* calculate size_sum and ensure dyn_size is enough for early alloc */
        size_sum = PFN_ALIGN(static_size + reserved_size +
                            max_t(size_t, dyn_size, PERCPU_DYNAMIC_EARLY_SIZE));
        dyn_size = size_sum - static_size - reserved_size;

        /*
         * Determine min_unit_size, alloc_size and max_upa such that
         * alloc_size is multiple of atom_size and is the smallest
         * which can accommodate 4k aligned segments which are equal to
         * or larger than min_unit_size.
         */
        min_unit_size = max_t(size_t, size_sum, PCPU_MIN_UNIT_SIZE);

        /* determine the maximum # of units that can fit in an allocation */
        alloc_size = roundup(min_unit_size, atom_size);
        upa = alloc_size / min_unit_size;
        while (alloc_size % upa || (offset_in_page(alloc_size / upa)))
                upa--;
        max_upa = upa;

        /* group cpus according to their proximity */
        for_each_possible_cpu(cpu) {
                group = 0;
        next_group:
                for_each_possible_cpu(tcpu) {
                        if (cpu == tcpu)
                                break;
                        if (group_map[tcpu] == group && cpu_distance_fn &&
                            (cpu_distance_fn(cpu, tcpu) > LOCAL_DISTANCE ||
                             cpu_distance_fn(tcpu, cpu) > LOCAL_DISTANCE)) {
                                group++;
                                nr_groups = max(nr_groups, group + 1);
                                goto next_group;
                        }
                }
                group_map[cpu] = group;
                group_cnt[group]++;
        }

        /*
         * Wasted space is caused by a ratio imbalance of upa to group_cnt.
         * Expand the unit_size until we use >= 75% of the units allocated.
         * Related to atom_size, which could be much larger than the unit_size.
         */
        last_allocs = INT_MAX;
        for (upa = max_upa; upa; upa--) {
                int allocs = 0, wasted = 0;

                if (alloc_size % upa || (offset_in_page(alloc_size / upa)))
                        continue;

                for (group = 0; group < nr_groups; group++) {
                        int this_allocs = DIV_ROUND_UP(group_cnt[group], upa);
                        allocs += this_allocs;
                        wasted += this_allocs * upa - group_cnt[group];
                }

                /*
                 * Don't accept if wastage is over 1/3.  The
                 * greater-than comparison ensures upa==1 always
                 * passes the following check.
                 */
                if (wasted > num_possible_cpus() / 3)
                        continue;

                /* and then don't consume more memory */
                if (allocs > last_allocs)
                        break;
                last_allocs = allocs;
                best_upa = upa;
        }
        upa = best_upa;

        /* allocate and fill alloc_info */
        for (group = 0; group < nr_groups; group++)
                nr_units += roundup(group_cnt[group], upa);

        ai = pcpu_alloc_alloc_info(nr_groups, nr_units);
        if (!ai)
                return ERR_PTR(-ENOMEM);
        cpu_map = ai->groups[0].cpu_map;

        for (group = 0; group < nr_groups; group++) {
                ai->groups[group].cpu_map = cpu_map;
                cpu_map += roundup(group_cnt[group], upa);
        }

        ai->static_size = static_size;
        ai->reserved_size = reserved_size;
        ai->dyn_size = dyn_size;
        ai->unit_size = alloc_size / upa;
        ai->atom_size = atom_size;
        ai->alloc_size = alloc_size;

        for (group = 0, unit = 0; group < nr_groups; group++) {
                struct pcpu_group_info *gi = &ai->groups[group];

                /*
                 * Initialize base_offset as if all groups are located
                 * back-to-back.  The caller should update this to
                 * reflect actual allocation.
                 */
                gi->base_offset = unit * ai->unit_size;

                for_each_possible_cpu(cpu)
                        if (group_map[cpu] == group)
                                gi->cpu_map[gi->nr_units++] = cpu;
                gi->nr_units = roundup(gi->nr_units, upa);
                unit += gi->nr_units;
        }
        BUG_ON(unit != nr_units);

        return ai;
}
#endif /* BUILD_EMBED_FIRST_CHUNK || BUILD_PAGE_FIRST_CHUNK */

#if defined(BUILD_EMBED_FIRST_CHUNK)
/**
 * pcpu_embed_first_chunk - embed the first percpu chunk into bootmem
 * @reserved_size: the size of reserved percpu area in bytes
 * @dyn_size: minimum free size for dynamic allocation in bytes
 * @atom_size: allocation atom size
 * @cpu_distance_fn: callback to determine distance between cpus, optional
 * @alloc_fn: function to allocate percpu page
 * @free_fn: function to free percpu page
 *
 * This is a helper to ease setting up embedded first percpu chunk and
 * can be called where pcpu_setup_first_chunk() is expected.
 *
 * If this function is used to setup the first chunk, it is allocated
 * by calling @alloc_fn and used as-is without being mapped into
 * vmalloc area.  Allocations are always whole multiples of @atom_size
 * aligned to @atom_size.
 *
 * This enables the first chunk to piggy back on the linear physical
 * mapping which often uses larger page size.  Please note that this
 * can result in very sparse cpu->unit mapping on NUMA machines thus
 * requiring large vmalloc address space.  Don't use this allocator if
 * vmalloc space is not orders of magnitude larger than distances
 * between node memory addresses (ie. 32bit NUMA machines).
 *
 * @dyn_size specifies the minimum dynamic area size.
 *
 * If the needed size is smaller than the minimum or specified unit
 * size, the leftover is returned using @free_fn.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
                                  size_t atom_size,
                                  pcpu_fc_cpu_distance_fn_t cpu_distance_fn,
                                  pcpu_fc_alloc_fn_t alloc_fn,
                                  pcpu_fc_free_fn_t free_fn)
{
        void *base = (void *)ULONG_MAX;
        void **areas = NULL;
        struct pcpu_alloc_info *ai;
        size_t size_sum, areas_size;
        unsigned long max_distance;
        int group, i, highest_group, rc;

        ai = pcpu_build_alloc_info(reserved_size, dyn_size, atom_size,
                                   cpu_distance_fn);
        if (IS_ERR(ai))
                return PTR_ERR(ai);

        size_sum = ai->static_size + ai->reserved_size + ai->dyn_size;
        areas_size = PFN_ALIGN(ai->nr_groups * sizeof(void *));

        areas = memblock_alloc(areas_size, SMP_CACHE_BYTES);
        if (!areas) {
                rc = -ENOMEM;
                goto out_free;
        }

        /* allocate, copy and determine base address & max_distance */
        highest_group = 0;
        for (group = 0; group < ai->nr_groups; group++) {
                struct pcpu_group_info *gi = &ai->groups[group];
                unsigned int cpu = NR_CPUS;
                void *ptr;

                for (i = 0; i < gi->nr_units && cpu == NR_CPUS; i++)
                        cpu = gi->cpu_map[i];
                BUG_ON(cpu == NR_CPUS);

                /* allocate space for the whole group */
                ptr = alloc_fn(cpu, gi->nr_units * ai->unit_size, atom_size);
                if (!ptr) {
                        rc = -ENOMEM;
                        goto out_free_areas;
                }
                /* kmemleak tracks the percpu allocations separately */
                kmemleak_free(ptr);
                areas[group] = ptr;

                base = min(ptr, base);
                if (ptr > areas[highest_group])
                        highest_group = group;
        }
        max_distance = areas[highest_group] - base;
        max_distance += ai->unit_size * ai->groups[highest_group].nr_units;

        /* warn if maximum distance is further than 75% of vmalloc space */
        if (max_distance > VMALLOC_TOTAL * 3 / 4) {
                pr_warn("max_distance=0x%lx too large for vmalloc space 0x%lx\n",
                                max_distance, VMALLOC_TOTAL);
#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
                /* and fail if we have fallback */
                rc = -EINVAL;
                goto out_free_areas;
#endif
        }

        /*
         * Copy data and free unused parts.  This should happen after all
         * allocations are complete; otherwise, we may end up with
         * overlapping groups.
         */
        for (group = 0; group < ai->nr_groups; group++) {
                struct pcpu_group_info *gi = &ai->groups[group];
                void *ptr = areas[group];

                for (i = 0; i < gi->nr_units; i++, ptr += ai->unit_size) {
                        if (gi->cpu_map[i] == NR_CPUS) {
                                /* unused unit, free whole */
                                free_fn(ptr, ai->unit_size);
                                continue;
                        }
                        /* copy and return the unused part */
                        memcpy(ptr, __per_cpu_load, ai->static_size);
                        free_fn(ptr + size_sum, ai->unit_size - size_sum);
                }
        }

        /* base address is now known, determine group base offsets */
        for (group = 0; group < ai->nr_groups; group++) {
                ai->groups[group].base_offset = areas[group] - base;
        }

        pr_info("Embedded %zu pages/cpu @%p s%zu r%zu d%zu u%zu\n",
                PFN_DOWN(size_sum), base, ai->static_size, ai->reserved_size,
                ai->dyn_size, ai->unit_size);

        rc = pcpu_setup_first_chunk(ai, base);
        goto out_free;

out_free_areas:
        for (group = 0; group < ai->nr_groups; group++)
                if (areas[group])
                        free_fn(areas[group],
                                ai->groups[group].nr_units * ai->unit_size);
out_free:
        pcpu_free_alloc_info(ai);
        if (areas)
                memblock_free_early(__pa(areas), areas_size);
        return rc;
}
#endif /* BUILD_EMBED_FIRST_CHUNK */

#ifdef BUILD_PAGE_FIRST_CHUNK
/**
 * pcpu_page_first_chunk - map the first chunk using PAGE_SIZE pages
 * @reserved_size: the size of reserved percpu area in bytes
 * @alloc_fn: function to allocate percpu page, always called with PAGE_SIZE
 * @free_fn: function to free percpu page, always called with PAGE_SIZE
 * @populate_pte_fn: function to populate pte
 *
 * This is a helper to ease setting up page-remapped first percpu
 * chunk and can be called where pcpu_setup_first_chunk() is expected.
 *
 * This is the basic allocator.  Static percpu area is allocated
 * page-by-page into vmalloc area.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
int __init pcpu_page_first_chunk(size_t reserved_size,
                                 pcpu_fc_alloc_fn_t alloc_fn,
                                 pcpu_fc_free_fn_t free_fn,
                                 pcpu_fc_populate_pte_fn_t populate_pte_fn)
{
        static struct vm_struct vm;
        struct pcpu_alloc_info *ai;
        char psize_str[16];
        int unit_pages;
        size_t pages_size;
        struct page **pages;
        int unit, i, j, rc;
        int upa;
        int nr_g0_units;

        snprintf(psize_str, sizeof(psize_str), "%luK", PAGE_SIZE >> 10);

        ai = pcpu_build_alloc_info(reserved_size, 0, PAGE_SIZE, NULL);
        if (IS_ERR(ai))
                return PTR_ERR(ai);
        BUG_ON(ai->nr_groups != 1);
        upa = ai->alloc_size/ai->unit_size;
        nr_g0_units = roundup(num_possible_cpus(), upa);
        if (WARN_ON(ai->groups[0].nr_units != nr_g0_units)) {
                pcpu_free_alloc_info(ai);
                return -EINVAL;
        }

        unit_pages = ai->unit_size >> PAGE_SHIFT;

        /* unaligned allocations can't be freed, round up to page size */
        pages_size = PFN_ALIGN(unit_pages * num_possible_cpus() *
                               sizeof(pages[0]));
        pages = memblock_alloc(pages_size, SMP_CACHE_BYTES);
        if (!pages)
                panic("%s: Failed to allocate %zu bytes\n", __func__,
                      pages_size);

        /* allocate pages */
        j = 0;
        for (unit = 0; unit < num_possible_cpus(); unit++) {
                unsigned int cpu = ai->groups[0].cpu_map[unit];
                for (i = 0; i < unit_pages; i++) {
                        void *ptr;

                        ptr = alloc_fn(cpu, PAGE_SIZE, PAGE_SIZE);
                        if (!ptr) {
                                pr_warn("failed to allocate %s page for cpu%u\n",
                                                psize_str, cpu);
                                goto enomem;
                        }
                        /* kmemleak tracks the percpu allocations separately */
                        kmemleak_free(ptr);
                        pages[j++] = virt_to_page(ptr);
                }
        }

        /* allocate vm area, map the pages and copy static data */
        vm.flags = VM_ALLOC;
        vm.size = num_possible_cpus() * ai->unit_size;
        vm_area_register_early(&vm, PAGE_SIZE);

        for (unit = 0; unit < num_possible_cpus(); unit++) {
                unsigned long unit_addr =
                        (unsigned long)vm.addr + unit * ai->unit_size;

                for (i = 0; i < unit_pages; i++)
                        populate_pte_fn(unit_addr + (i << PAGE_SHIFT));

                /* pte already populated, the following shouldn't fail */
                rc = __pcpu_map_pages(unit_addr, &pages[unit * unit_pages],
                                      unit_pages);
                if (rc < 0)
                        panic("failed to map percpu area, err=%d\n", rc);

                /*
                 * FIXME: Archs with virtual cache should flush local
                 * cache for the linear mapping here - something
                 * equivalent to flush_cache_vmap() on the local cpu.
                 * flush_cache_vmap() can't be used as most supporting
                 * data structures are not set up yet.
                 */

                /* copy static data */
                memcpy((void *)unit_addr, __per_cpu_load, ai->static_size);
        }

        /* we're ready, commit */
        pr_info("%d %s pages/cpu @%p s%zu r%zu d%zu\n",
                unit_pages, psize_str, vm.addr, ai->static_size,
                ai->reserved_size, ai->dyn_size);

        rc = pcpu_setup_first_chunk(ai, vm.addr);
        goto out_free_ar;

enomem:
        while (--j >= 0)
                free_fn(page_address(pages[j]), PAGE_SIZE);
        rc = -ENOMEM;
out_free_ar:
        memblock_free_early(__pa(pages), pages_size);
        pcpu_free_alloc_info(ai);
        return rc;
}
#endif /* BUILD_PAGE_FIRST_CHUNK */

#ifndef CONFIG_HAVE_SETUP_PER_CPU_AREA
/*
 * Generic SMP percpu area setup.
 *
 * The embedding helper is used because its behavior closely resembles
 * the original non-dynamic generic percpu area setup.  This is
 * important because many archs have addressing restrictions and might
 * fail if the percpu area is located far away from the previous
 * location.  As an added bonus, in non-NUMA cases, embedding is
 * generally a good idea TLB-wise because percpu area can piggy back
 * on the physical linear memory mapping which uses large page
 * mappings on applicable archs.
 */
unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
EXPORT_SYMBOL(__per_cpu_offset);

static void * __init pcpu_dfl_fc_alloc(unsigned int cpu, size_t size,
                                       size_t align)
{
        return  memblock_alloc_from(size, align, __pa(MAX_DMA_ADDRESS));
}

static void __init pcpu_dfl_fc_free(void *ptr, size_t size)
{
        memblock_free_early(__pa(ptr), size);
}

void __init setup_per_cpu_areas(void)
{
        unsigned long delta;
        unsigned int cpu;
        int rc;

        /*
         * Always reserve area for module percpu variables.  That's
         * what the legacy allocator did.
         */
        rc = pcpu_embed_first_chunk(PERCPU_MODULE_RESERVE,
                                    PERCPU_DYNAMIC_RESERVE, PAGE_SIZE, NULL,
                                    pcpu_dfl_fc_alloc, pcpu_dfl_fc_free);
        if (rc < 0)
                panic("Failed to initialize percpu areas.");

        delta = (unsigned long)pcpu_base_addr - (unsigned long)__per_cpu_start;
        for_each_possible_cpu(cpu)
                __per_cpu_offset[cpu] = delta + pcpu_unit_offsets[cpu];
}
#endif  /* CONFIG_HAVE_SETUP_PER_CPU_AREA */

#else   /* CONFIG_SMP */

/*
 * UP percpu area setup.
 *
 * UP always uses km-based percpu allocator with identity mapping.
 * Static percpu variables are indistinguishable from the usual static
 * variables and don't require any special preparation.
 */
void __init setup_per_cpu_areas(void)
{
        const size_t unit_size =
                roundup_pow_of_two(max_t(size_t, PCPU_MIN_UNIT_SIZE,
                                         PERCPU_DYNAMIC_RESERVE));
        struct pcpu_alloc_info *ai;
        void *fc;

        ai = pcpu_alloc_alloc_info(1, 1);
        fc = memblock_alloc_from(unit_size, PAGE_SIZE, __pa(MAX_DMA_ADDRESS));
        if (!ai || !fc)
                panic("Failed to allocate memory for percpu areas.");
        /* kmemleak tracks the percpu allocations separately */
        kmemleak_free(fc);

        ai->dyn_size = unit_size;
        ai->unit_size = unit_size;
        ai->atom_size = unit_size;
        ai->alloc_size = unit_size;
        ai->groups[0].nr_units = 1;
        ai->groups[0].cpu_map[0] = 0;

        if (pcpu_setup_first_chunk(ai, fc) < 0)
                panic("Failed to initialize percpu areas.");
        pcpu_free_alloc_info(ai);
}

#endif  /* CONFIG_SMP */

/*
 * pcpu_nr_pages - calculate total number of populated backing pages
 *
 * This reflects the number of pages populated to back chunks.  Metadata is
 * excluded in the number exposed in meminfo as the number of backing pages
 * scales with the number of cpus and can quickly outweigh the memory used for
 * metadata.  It also keeps this calculation nice and simple.
 *
 * RETURNS:
 * Total number of populated backing pages in use by the allocator.
 */
unsigned long pcpu_nr_pages(void)
{
        return pcpu_nr_populated * pcpu_nr_units;
}

/*
 * Percpu allocator is initialized early during boot when neither slab or
 * workqueue is available.  Plug async management until everything is up
 * and running.
 */
static int __init percpu_enable_async(void)
{
        pcpu_async_enabled = true;
        return 0;
}
subsys_initcall(percpu_enable_async);