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 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * 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 <dennis@kernel.org>
  *
  * 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
  * memcg-awareness.  To make a percpu allocation memcg-aware the __GFP_ACCOUNT
  * flag should be passed.  All memcg-aware allocations are sharing one set
  * of chunks and all unaccounted allocations and allocations performed
  * by processes belonging to the root memory cgroup are using the second set.
  *
  * The allocator 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/cpumask.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 <linux/sched/mm.h>
 #include <linux/memcontrol.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 the size of the biggest continuous free area.
  * 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 int pcpu_free_slot __ro_after_init;
 int pcpu_sidelined_slot __ro_after_init;
 int pcpu_to_depopulate_slot __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;
 
 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_chunk_lists __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_free_slot;
     return __pcpu_size_to_slot(size);
 }
 
 static int pcpu_chunk_slot(const struct pcpu_chunk *chunk)
 {
     const struct pcpu_block_md *chunk_md = &chunk->chunk_md;
 
     if (chunk->free_bytes < PCPU_MIN_ALLOC_SIZE ||
         chunk_md->contig_hint == 0)
         return 0;
 
     return pcpu_size_to_slot(chunk_md->contig_hint * 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);
 }
 
 /*
  * 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_check_block_hint - check against the contig hint
  * @block: block of interest
  * @bits: size of allocation
  * @align: alignment of area (max PAGE_SIZE)
  *
  * Check to see if the allocation can fit in the block's contig hint.
  * Note, a chunk uses the same hints as a block so this can also check against
  * the chunk's contig hint.
  */
 static bool pcpu_check_block_hint(struct pcpu_block_md *block, int bits,
                   size_t align)
 {
     int bit_off = ALIGN(block->contig_hint_start, align) -
         block->contig_hint_start;
 
     return bit_off + bits <= block->contig_hint;
 }
 
 /*
  * 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);
 }
 
 /**
  * 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_chunk_lists[slot]);
         else
             list_move_tail(&chunk->list, &pcpu_chunk_lists[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);
 
     /* leave isolated chunks in-place */
     if (chunk->isolated)
         return;
 
     if (oslot != nslot)
         __pcpu_chunk_move(chunk, nslot, oslot < nslot);
 }
 
 static void pcpu_isolate_chunk(struct pcpu_chunk *chunk)
 {
     lockdep_assert_held(&pcpu_lock);
 
     if (!chunk->isolated) {
         chunk->isolated = true;
         pcpu_nr_empty_pop_pages -= chunk->nr_empty_pop_pages;
     }
     list_move(&chunk->list, &pcpu_chunk_lists[pcpu_to_depopulate_slot]);
 }
 
 static void pcpu_reintegrate_chunk(struct pcpu_chunk *chunk)
 {
     lockdep_assert_held(&pcpu_lock);
 
     if (chunk->isolated) {
         chunk->isolated = false;
         pcpu_nr_empty_pop_pages += chunk->nr_empty_pop_pages;
         pcpu_chunk_relocate(chunk, -1);
     }
 }
 
 /*
  * 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 && !chunk->isolated)
         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_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 == block->nr_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_update_scan - update a block given a free area from a scan
  * @chunk: chunk of interest
  * @bit_off: chunk offset
  * @bits: size of free area
  *
  * Finding the final allocation spot first goes through pcpu_find_block_fit()
  * to find a block that can hold the allocation and then pcpu_alloc_area()
  * where a scan is used.  When allocations require specific alignments,
  * we can inadvertently create holes which will not be seen in the alloc
  * or free paths.
  *
  * This takes a given free area hole and updates a block as it may change the
  * scan_hint.  We need to scan backwards to ensure we don't miss free bits
  * from alignment.
  */
 static void pcpu_block_update_scan(struct pcpu_chunk *chunk, int bit_off,
                    int bits)
 {
     int s_off = pcpu_off_to_block_off(bit_off);
     int e_off = s_off + bits;
     int s_index, l_bit;
     struct pcpu_block_md *block;
 
     if (e_off > PCPU_BITMAP_BLOCK_BITS)
         return;
 
     s_index = pcpu_off_to_block_index(bit_off);
     block = chunk->md_blocks + s_index;
 
     /* scan backwards in case of alignment skipping free bits */
     l_bit = find_last_bit(pcpu_index_alloc_map(chunk, s_index), s_off);
     s_off = (s_off == l_bit) ? 0 : l_bit + 1;
 
     pcpu_block_update(block, s_off, e_off);
 }
 
 /**
  * pcpu_chunk_refresh_hint - updates metadata about a chunk
  * @chunk: chunk of interest
  * @full_scan: if we should scan from the beginning
  *
  * Iterates over the metadata blocks to find the largest contig area.
  * A full scan can be avoided on the allocation path as this is triggered
  * if we broke the contig_hint.  In doing so, the scan_hint will be before
  * the contig_hint or after if the scan_hint == contig_hint.  This cannot
  * be prevented on freeing as we want to find the largest area possibly
  * spanning blocks.
  */
 static void pcpu_chunk_refresh_hint(struct pcpu_chunk *chunk, bool full_scan)
 {
     struct pcpu_block_md *chunk_md = &chunk->chunk_md;
     int bit_off, bits;
 
     /* promote scan_hint to contig_hint */
     if (!full_scan && chunk_md->scan_hint) {
         bit_off = chunk_md->scan_hint_start + chunk_md->scan_hint;
         chunk_md->contig_hint_start = chunk_md->scan_hint_start;
         chunk_md->contig_hint = chunk_md->scan_hint;
         chunk_md->scan_hint = 0;
     } else {
         bit_off = chunk_md->first_free;
         chunk_md->contig_hint = 0;
     }
 
     bits = 0;
     pcpu_for_each_md_free_region(chunk, bit_off, bits)
         pcpu_block_update(chunk_md, bit_off, bit_off + bits);
 }
 
 /**
  * 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);
     unsigned int start, end;    /* region start, region end */
 
     /* promote scan_hint to contig_hint */
     if (block->scan_hint) {
         start = block->scan_hint_start + block->scan_hint;
         block->contig_hint_start = block->scan_hint_start;
         block->contig_hint = block->scan_hint;
         block->scan_hint = 0;
     } else {
         start = block->first_free;
         block->contig_hint = 0;
     }
 
     block->right_free = 0;
 
     /* iterate over free areas and update the contig hints */
     for_each_clear_bitrange_from(start, end, alloc_map, PCPU_BITMAP_BLOCK_BITS)
         pcpu_block_update(block, start, end);
 }
 
 /**
  * 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)
 {
     struct pcpu_block_md *chunk_md = &chunk->chunk_md;
     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 */
         if (!s_off)
             s_block->left_free = 0;
         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;
 
             e_block->left_free = 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->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);
 
     if (pcpu_region_overlap(chunk_md->scan_hint_start,
                 chunk_md->scan_hint_start +
                 chunk_md->scan_hint,
                 bit_off,
                 bit_off + bits))
         chunk_md->scan_hint = 0;
 
     /*
      * 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_md->contig_hint_start,
                 chunk_md->contig_hint_start +
                 chunk_md->contig_hint,
                 bit_off,
                 bit_off + bits))
         pcpu_chunk_refresh_hint(chunk, false);
 }
 
 /**
  * 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_md->contig_hint.
  * chunk_md->contig_hint 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, true);
     else
         pcpu_block_update(&chunk->chunk_md,
                   pcpu_block_off_to_off(s_index, start),
                   end);
 }
 
 /**
  * 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)
 {
     unsigned int start, end;
 
     start = PFN_DOWN(bit_off * PCPU_MIN_ALLOC_SIZE);
     end = PFN_UP((bit_off + bits) * PCPU_MIN_ALLOC_SIZE);
 
     start = find_next_zero_bit(chunk->populated, end, start);
     if (start >= end)
         return true;
 
     end = find_next_bit(chunk->populated, end, start + 1);
 
     *next_off = end * 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)
 {
     struct pcpu_block_md *chunk_md = &chunk->chunk_md;
     int bit_off, bits, next_off;
 
     /*
      * This is an optimization to prevent scanning by assuming if the
      * allocation cannot fit in the global hint, there is memory pressure
      * and creating a new chunk would happen soon.
      */
     if (!pcpu_check_block_hint(chunk_md, alloc_bits, align))
         return -1;
 
     bit_off = pcpu_next_hint(chunk_md, alloc_bits);
     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_find_zero_area - modified from bitmap_find_next_zero_area_off()
  * @map: the address to base the search on
  * @size: the bitmap size in bits
  * @start: the bitnumber to start searching at
  * @nr: the number of zeroed bits we're looking for
  * @align_mask: alignment mask for zero area
  * @largest_off: offset of the largest area skipped
  * @largest_bits: size of the largest area skipped
  *
  * The @align_mask should be one less than a power of 2.
  *
  * This is a modified version of bitmap_find_next_zero_area_off() to remember
  * the largest area that was skipped.  This is imperfect, but in general is
  * good enough.  The largest remembered region is the largest failed region
  * seen.  This does not include anything we possibly skipped due to alignment.
  * pcpu_block_update_scan() does scan backwards to try and recover what was
  * lost to alignment.  While this can cause scanning to miss earlier possible
  * free areas, smaller allocations will eventually fill those holes.
  */
 static unsigned long pcpu_find_zero_area(unsigned long *map,
                      unsigned long size,
                      unsigned long start,
                      unsigned long nr,
                      unsigned long align_mask,
                      unsigned long *largest_off,
                      unsigned long *largest_bits)
 {
     unsigned long index, end, i, area_off, area_bits;
 again:
     index = find_next_zero_bit(map, size, start);
 
     /* Align allocation */
     index = __ALIGN_MASK(index, align_mask);
     area_off = index;
 
     end = index + nr;
     if (end > size)
         return end;
     i = find_next_bit(map, end, index);
     if (i < end) {
         area_bits = i - area_off;
         /* remember largest unused area with best alignment */
         if (area_bits > *largest_bits ||
             (area_bits == *largest_bits && *largest_off &&
              (!area_off || __ffs(area_off) > __ffs(*largest_off)))) {
             *largest_off = area_off;
             *largest_bits = area_bits;
         }
 
         start = i + 1;
         goto again;
     }
     return index;
 }
 
 /**
  * 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)
 {
     struct pcpu_block_md *chunk_md = &chunk->chunk_md;
     size_t align_mask = (align) ? (align - 1) : 0;
     unsigned long area_off = 0, area_bits = 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 = pcpu_find_zero_area(chunk->alloc_map, end, start, alloc_bits,
                       align_mask, &area_off, &area_bits);
     if (bit_off >= end)
         return -1;
 
     if (area_bits)
         pcpu_block_update_scan(chunk, area_off, area_bits);
 
     /* 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_md->first_free)
         chunk_md->first_free = 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.
  *
  * RETURNS:
  * Number of freed bytes.
  */
 static int pcpu_free_area(struct pcpu_chunk *chunk, int off)
 {
     struct pcpu_block_md *chunk_md = &chunk->chunk_md;
     int bit_off, bits, end, oslot, freed;
 
     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);
 
     freed = bits * PCPU_MIN_ALLOC_SIZE;
 
     /* update metadata */
     chunk->free_bytes += freed;
 
     /* update first free bit */
     chunk_md->first_free = min(chunk_md->first_free, bit_off);
 
     pcpu_block_update_hint_free(chunk, bit_off, bits);
 
     pcpu_chunk_relocate(chunk, oslot);
 
     return freed;
 }
 
 static void pcpu_init_md_block(struct pcpu_block_md *block, int nr_bits)
 {
     block->scan_hint = 0;
     block->contig_hint = nr_bits;
     block->left_free = nr_bits;
     block->right_free = nr_bits;
     block->first_free = 0;
     block->nr_bits = nr_bits;
 }
 
 static void pcpu_init_md_blocks(struct pcpu_chunk *chunk)
 {
     struct pcpu_block_md *md_block;
 
     /* init the chunk's block */
     pcpu_init_md_block(&chunk->chunk_md, pcpu_chunk_map_bits(chunk));
 
     for (md_block = chunk->md_blocks;
          md_block != chunk->md_blocks + pcpu_chunk_nr_blocks(chunk);
          md_block++)
         pcpu_init_md_block(md_block, 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 = struct_size(chunk, populated,
                  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);
 
 #ifdef CONFIG_MEMCG_KMEM
     /* first chunk is free to use */
     chunk->obj_cgroups = NULL;
 #endif
     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->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->chunk_md.first_free = 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;
 
 #ifdef CONFIG_MEMCG_KMEM
     if (!mem_cgroup_kmem_disabled()) {
         chunk->obj_cgroups =
             pcpu_mem_zalloc(pcpu_chunk_map_bits(chunk) *
                     sizeof(struct obj_cgroup *), gfp);
         if (!chunk->obj_cgroups)
             goto objcg_fail;
     }
 #endif
 
     pcpu_init_md_blocks(chunk);
 
     /* init metadata */
     chunk->free_bytes = chunk->nr_pages * PAGE_SIZE;
 
     return chunk;
 
 #ifdef CONFIG_MEMCG_KMEM
 objcg_fail:
     pcpu_mem_free(chunk->md_blocks);
 #endif
 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;
 #ifdef CONFIG_MEMCG_KMEM
     pcpu_mem_free(chunk->obj_cgroups);
 #endif
     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.
  */
 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_post_unmap_tlb_flush    - flush tlb for 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 void pcpu_post_unmap_tlb_flush(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));
 }
 
 #ifdef CONFIG_MEMCG_KMEM
 static bool pcpu_memcg_pre_alloc_hook(size_t size, gfp_t gfp,
                       struct obj_cgroup **objcgp)
 {
     struct obj_cgroup *objcg;
 
     if (!memcg_kmem_enabled() || !(gfp & __GFP_ACCOUNT))
         return true;
 
     objcg = get_obj_cgroup_from_current();
     if (!objcg)
         return true;
 
     if (obj_cgroup_charge(objcg, gfp, pcpu_obj_full_size(size))) {
         obj_cgroup_put(objcg);
         return false;
     }
 
     *objcgp = objcg;
     return true;
 }
 
 static void pcpu_memcg_post_alloc_hook(struct obj_cgroup *objcg,
                        struct pcpu_chunk *chunk, int off,
                        size_t size)
 {
     if (!objcg)
         return;
 
     if (likely(chunk && chunk->obj_cgroups)) {
         chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT] = objcg;
 
         rcu_read_lock();
         mod_memcg_state(obj_cgroup_memcg(objcg), MEMCG_PERCPU_B,
                 pcpu_obj_full_size(size));
         rcu_read_unlock();
     } else {
         obj_cgroup_uncharge(objcg, pcpu_obj_full_size(size));
         obj_cgroup_put(objcg);
     }
 }
 
 static void pcpu_memcg_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
 {
     struct obj_cgroup *objcg;
 
     if (unlikely(!chunk->obj_cgroups))
         return;
 
     objcg = chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT];
     if (!objcg)
         return;
     chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT] = NULL;
 
     obj_cgroup_uncharge(objcg, pcpu_obj_full_size(size));
 
     rcu_read_lock();
     mod_memcg_state(obj_cgroup_memcg(objcg), MEMCG_PERCPU_B,
             -pcpu_obj_full_size(size));
     rcu_read_unlock();
 
     obj_cgroup_put(objcg);
 }
 
 #else /* CONFIG_MEMCG_KMEM */
 static bool
 pcpu_memcg_pre_alloc_hook(size_t size, gfp_t gfp, struct obj_cgroup **objcgp)
 {
     return true;
 }
 
 static void pcpu_memcg_post_alloc_hook(struct obj_cgroup *objcg,
                        struct pcpu_chunk *chunk, int off,
                        size_t size)
 {
 }
 
 static void pcpu_memcg_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
 {
 }
 #endif /* CONFIG_MEMCG_KMEM */
 
 /**
  * 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)
 {
     gfp_t pcpu_gfp;
     bool is_atomic;
     bool do_warn;
     struct obj_cgroup *objcg = NULL;
     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;
 
     gfp = current_gfp_context(gfp);
     /* whitelisted flags that can be passed to the backing allocators */
     pcpu_gfp = gfp & (GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN);
     is_atomic = (gfp & GFP_KERNEL) != GFP_KERNEL;
     do_warn = !(gfp & __GFP_NOWARN);
 
     /*
      * 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 (unlikely(!pcpu_memcg_pre_alloc_hook(size, gfp, &objcg)))
         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)) {
             pcpu_memcg_post_alloc_hook(objcg, NULL, 0, size);
             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_free_slot; slot++) {
         list_for_each_entry_safe(chunk, next, &pcpu_chunk_lists[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) {
                 pcpu_reintegrate_chunk(chunk);
                 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_chunk_lists[pcpu_free_slot])) {
         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) {
         unsigned int page_end, rs, re;
 
         rs = PFN_DOWN(off);
         page_end = PFN_UP(off + size);
 
         for_each_clear_bitrange_from(rs, re, chunk->populated, 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(_RET_IP_, reserved, is_atomic, size, align,
                   chunk->base_addr, off, ptr,
                   pcpu_obj_full_size(size), gfp);
 
     pcpu_memcg_post_alloc_hook(objcg, chunk, off, size);
 
     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_balance_workfn() */
         pcpu_atomic_alloc_failed = true;
         pcpu_schedule_balance_work();
     } else {
         mutex_unlock(&pcpu_alloc_mutex);
     }
 
     pcpu_memcg_post_alloc_hook(objcg, NULL, 0, size);
 
     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_free - manage the amount of free chunks
  * @empty_only: free chunks only if there are no populated pages
  *
  * If empty_only is %false, reclaim all fully free chunks regardless of the
  * number of populated pages.  Otherwise, only reclaim chunks that have no
  * populated pages.
  *
  * CONTEXT:
  * pcpu_lock (can be dropped temporarily)
  */
 static void pcpu_balance_free(bool empty_only)
 {
     LIST_HEAD(to_free);
     struct list_head *free_head = &pcpu_chunk_lists[pcpu_free_slot];
     struct pcpu_chunk *chunk, *next;
 
     lockdep_assert_held(&pcpu_lock);
 
     /*
      * There's no reason to keep around multiple unused chunks and VM
      * areas can be scarce.  Destroy all free chunks except for one.
      */
     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;
 
         if (!empty_only || chunk->nr_empty_pop_pages == 0)
             list_move(&chunk->list, &to_free);
     }
 
     if (list_empty(&to_free))
         return;
 
     spin_unlock_irq(&pcpu_lock);
     list_for_each_entry_safe(chunk, next, &to_free, list) {
         unsigned int rs, re;
 
         for_each_set_bitrange(rs, re, chunk->populated, 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();
     }
     spin_lock_irq(&pcpu_lock);
 }
 
 /**
  * pcpu_balance_populated - manage the amount of populated pages
  *
  * Maintain a certain amount of populated pages to satisfy atomic allocations.
  * 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.
  *
  * CONTEXT:
  * pcpu_lock (can be dropped temporarily)
  */
 static void pcpu_balance_populated(void)
 {
     /* gfp flags passed to underlying allocators */
     const gfp_t gfp = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
     struct pcpu_chunk *chunk;
     int slot, nr_to_pop, ret;
 
     lockdep_assert_held(&pcpu_lock);
 
     /*
      * 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_free_slot; slot++) {
         unsigned int nr_unpop = 0, rs, re;
 
         if (!nr_to_pop)
             break;
 
         list_for_each_entry(chunk, &pcpu_chunk_lists[slot], list) {
             nr_unpop = chunk->nr_pages - chunk->nr_populated;
             if (nr_unpop)
                 break;
         }
 
         if (!nr_unpop)
             continue;
 
         /* @chunk can't go away while pcpu_alloc_mutex is held */
         for_each_clear_bitrange(rs, re, chunk->populated, chunk->nr_pages) {
             int nr = min_t(int, re - rs, nr_to_pop);
 
             spin_unlock_irq(&pcpu_lock);
             ret = pcpu_populate_chunk(chunk, rs, rs + nr, gfp);
             cond_resched();
             spin_lock_irq(&pcpu_lock);
             if (!ret) {
                 nr_to_pop -= nr;
                 pcpu_chunk_populated(chunk, rs, rs + nr);
             } 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 */
         spin_unlock_irq(&pcpu_lock);
         chunk = pcpu_create_chunk(gfp);
         cond_resched();
         spin_lock_irq(&pcpu_lock);
         if (chunk) {
             pcpu_chunk_relocate(chunk, -1);
             goto retry_pop;
         }
     }
 }
 
 /**
  * pcpu_reclaim_populated - scan over to_depopulate chunks and free empty pages
  *
  * Scan over chunks in the depopulate list and try to release unused populated
  * pages back to the system.  Depopulated chunks are sidelined to prevent
  * repopulating these pages unless required.  Fully free chunks are reintegrated
  * and freed accordingly (1 is kept around).  If we drop below the empty
  * populated pages threshold, reintegrate the chunk if it has empty free pages.
  * Each chunk is scanned in the reverse order to keep populated pages close to
  * the beginning of the chunk.
  *
  * CONTEXT:
  * pcpu_lock (can be dropped temporarily)
  *
  */
 static void pcpu_reclaim_populated(void)
 {
     struct pcpu_chunk *chunk;
     struct pcpu_block_md *block;
     int freed_page_start, freed_page_end;
     int i, end;
     bool reintegrate;
 
     lockdep_assert_held(&pcpu_lock);
 
     /*
      * Once a chunk is isolated to the to_depopulate list, the chunk is no
      * longer discoverable to allocations whom may populate pages.  The only
      * other accessor is the free path which only returns area back to the
      * allocator not touching the populated bitmap.
      */
     while (!list_empty(&pcpu_chunk_lists[pcpu_to_depopulate_slot])) {
         chunk = list_first_entry(&pcpu_chunk_lists[pcpu_to_depopulate_slot],
                      struct pcpu_chunk, list);
         WARN_ON(chunk->immutable);
 
         /*
          * Scan chunk's pages in the reverse order to keep populated
          * pages close to the beginning of the chunk.
          */
         freed_page_start = chunk->nr_pages;
         freed_page_end = 0;
         reintegrate = false;
         for (i = chunk->nr_pages - 1, end = -1; i >= 0; i--) {
             /* no more work to do */
             if (chunk->nr_empty_pop_pages == 0)
                 break;
 
             /* reintegrate chunk to prevent atomic alloc failures */
             if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_HIGH) {
                 reintegrate = true;
                 goto end_chunk;
             }
 
             /*
              * If the page is empty and populated, start or
              * extend the (i, end) range.  If i == 0, decrease
              * i and perform the depopulation to cover the last
              * (first) page in the chunk.
              */
             block = chunk->md_blocks + i;
             if (block->contig_hint == PCPU_BITMAP_BLOCK_BITS &&
                 test_bit(i, chunk->populated)) {
                 if (end == -1)
                     end = i;
                 if (i > 0)
                     continue;
                 i--;
             }
 
             /* depopulate if there is an active range */
             if (end == -1)
                 continue;
 
             spin_unlock_irq(&pcpu_lock);
             pcpu_depopulate_chunk(chunk, i + 1, end + 1);
             cond_resched();
             spin_lock_irq(&pcpu_lock);
 
             pcpu_chunk_depopulated(chunk, i + 1, end + 1);
             freed_page_start = min(freed_page_start, i + 1);
             freed_page_end = max(freed_page_end, end + 1);
 
             /* reset the range and continue */
             end = -1;
         }
 
 end_chunk:
         /* batch tlb flush per chunk to amortize cost */
         if (freed_page_start < freed_page_end) {
             spin_unlock_irq(&pcpu_lock);
             pcpu_post_unmap_tlb_flush(chunk,
                           freed_page_start,
                           freed_page_end);
             cond_resched();
             spin_lock_irq(&pcpu_lock);
         }
 
         if (reintegrate || chunk->free_bytes == pcpu_unit_size)
             pcpu_reintegrate_chunk(chunk);
         else
             list_move_tail(&chunk->list,
                        &pcpu_chunk_lists[pcpu_sidelined_slot]);
     }
 }
 
 /**
  * pcpu_balance_workfn - manage the amount of free chunks and populated pages
  * @work: unused
  *
  * For each chunk type, manage the number of fully free chunks and the number of
  * populated pages.  An important thing to consider is when pages are freed and
  * how they contribute to the global counts.
  */
 static void pcpu_balance_workfn(struct work_struct *work)
 {
     /*
      * pcpu_balance_free() is called twice because the first time we may
      * trim pages in the active pcpu_nr_empty_pop_pages which may cause us
      * to grow other chunks.  This then gives pcpu_reclaim_populated() time
      * to move fully free chunks to the active list to be freed if
      * appropriate.
      */
     mutex_lock(&pcpu_alloc_mutex);
     spin_lock_irq(&pcpu_lock);
 
     pcpu_balance_free(false);
     pcpu_reclaim_populated();
     pcpu_balance_populated();
     pcpu_balance_free(true);
 
     spin_unlock_irq(&pcpu_lock);
     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 size, off;
     bool need_balance = false;
 
     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;
 
     size = pcpu_free_area(chunk, off);
 
     pcpu_memcg_free_hook(chunk, off, size);
 
     /*
      * If there are more than one fully free chunks, wake up grim reaper.
      * If the chunk is isolated, it may be in the process of being
      * reclaimed.  Let reclaim manage cleaning up of that chunk.
      */
     if (!chunk->isolated && chunk->free_bytes == pcpu_unit_size) {
         struct pcpu_chunk *pos;
 
         list_for_each_entry(pos, &pcpu_chunk_lists[pcpu_free_slot], list)
             if (pos != chunk) {
                 need_balance = true;
                 break;
             }
     } else if (pcpu_should_reclaim_chunk(chunk)) {
         pcpu_isolate_chunk(chunk);
         need_balance = true;
     }
 
     trace_percpu_free_percpu(chunk->base_addr, off, ptr);
 
     spin_unlock_irqrestore(&pcpu_lock, flags);
 
     if (need_balance)
         pcpu_schedule_balance_work();
 }
 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(struct_size(ai, groups, nr_groups),
               __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(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
  * percpu 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.
  */
 void __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 = struct_size(chunk, populated,
                          BITS_TO_LONGS(pcpu_unit_pages));
 
     pcpu_stats_save_ai(ai);
 
     /*
      * Allocate chunk slots.  The slots after the active slots are:
      *   sidelined_slot - isolated, depopulated chunks
      *   free_slot - fully free chunks
      *   to_depopulate_slot - isolated, chunks to depopulate
      */
     pcpu_sidelined_slot = __pcpu_size_to_slot(pcpu_unit_size) + 1;
     pcpu_free_slot = pcpu_sidelined_slot + 1;
     pcpu_to_depopulate_slot = pcpu_free_slot + 1;
     pcpu_nr_slots = pcpu_to_depopulate_slot + 1;
     pcpu_chunk_lists = memblock_alloc(pcpu_nr_slots *
                       sizeof(pcpu_chunk_lists[0]),
                       SMP_CACHE_BYTES);
     if (!pcpu_chunk_lists)
         panic("%s: Failed to allocate %zu bytes\n", __func__,
               pcpu_nr_slots * sizeof(pcpu_chunk_lists[0]));
 
     for (i = 0; i < pcpu_nr_slots; i++)
         INIT_LIST_HEAD(&pcpu_chunk_lists[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;
 }
 
 #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 __flatten 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;
     static struct cpumask mask __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, 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));
     cpumask_clear(&mask);
 
     /* 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;
 
     cpumask_copy(&mask, cpu_possible_mask);
 
     /* group cpus according to their proximity */
     for (group = 0; !cpumask_empty(&mask); group++) {
         /* pop the group's first cpu */
         cpu = cpumask_first(&mask);
         group_map[cpu] = group;
         group_cnt[group]++;
         cpumask_clear_cpu(cpu, &mask);
 
         for_each_cpu(tcpu, &mask) {
             if (!cpu_distance_fn ||
                 (cpu_distance_fn(cpu, tcpu) == LOCAL_DISTANCE &&
                  cpu_distance_fn(tcpu, cpu) == LOCAL_DISTANCE)) {
                 group_map[tcpu] = group;
                 group_cnt[group]++;
                 cpumask_clear_cpu(tcpu, &mask);
             }
         }
     }
     nr_groups = 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;
     best_upa = 0;
     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;
     }
     BUG_ON(!best_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;
 }
 
 static void * __init pcpu_fc_alloc(unsigned int cpu, size_t size, size_t align,
                    pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn)
 {
     const unsigned long goal = __pa(MAX_DMA_ADDRESS);
 #ifdef CONFIG_NUMA
     int node = NUMA_NO_NODE;
     void *ptr;
 
     if (cpu_to_nd_fn)
         node = cpu_to_nd_fn(cpu);
 
     if (node == NUMA_NO_NODE || !node_online(node) || !NODE_DATA(node)) {
         ptr = memblock_alloc_from(size, align, goal);
         pr_info("cpu %d has no node %d or node-local memory\n",
             cpu, node);
         pr_debug("per cpu data for cpu%d %zu bytes at 0x%llx\n",
              cpu, size, (u64)__pa(ptr));
     } else {
         ptr = memblock_alloc_try_nid(size, align, goal,
                          MEMBLOCK_ALLOC_ACCESSIBLE,
                          node);
 
         pr_debug("per cpu data for cpu%d %zu bytes on node%d at 0x%llx\n",
              cpu, size, node, (u64)__pa(ptr));
     }
     return ptr;
 #else
     return memblock_alloc_from(size, align, goal);
 #endif
 }
 
 static void __init pcpu_fc_free(void *ptr, size_t size)
 {
     memblock_free(ptr, size);
 }
 #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
  * @cpu_to_nd_fn: callback to convert cpu to it's node, optional
  *
  * 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 pcpu_fc_alloc 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 pcpu_fc_free.
  *
  * 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_cpu_to_node_fn_t cpu_to_nd_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 = 0;
 
     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 = pcpu_fc_alloc(cpu, gi->nr_units * ai->unit_size, atom_size, cpu_to_nd_fn);
         if (!ptr) {
             rc = -ENOMEM;
             goto out_free_areas;
         }
         /* kmemleak tracks the percpu allocations separately */
         kmemleak_ignore_phys(__pa(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 */
                 pcpu_fc_free(ptr, ai->unit_size);
                 continue;
             }
             /* copy and return the unused part */
             memcpy(ptr, __per_cpu_load, ai->static_size);
             pcpu_fc_free(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 s%zu r%zu d%zu u%zu\n",
         PFN_DOWN(size_sum), ai->static_size, ai->reserved_size,
         ai->dyn_size, ai->unit_size);
 
     pcpu_setup_first_chunk(ai, base);
     goto out_free;
 
 out_free_areas:
     for (group = 0; group < ai->nr_groups; group++)
         if (areas[group])
             pcpu_fc_free(areas[group],
                 ai->groups[group].nr_units * ai->unit_size);
 out_free:
     pcpu_free_alloc_info(ai);
     if (areas)
         memblock_free(areas, areas_size);
     return rc;
 }
 #endif /* BUILD_EMBED_FIRST_CHUNK */
 
 #ifdef BUILD_PAGE_FIRST_CHUNK
 #include <asm/pgalloc.h>
 
 #ifndef P4D_TABLE_SIZE
 #define P4D_TABLE_SIZE PAGE_SIZE
 #endif
 
 #ifndef PUD_TABLE_SIZE
 #define PUD_TABLE_SIZE PAGE_SIZE
 #endif
 
 #ifndef PMD_TABLE_SIZE
 #define PMD_TABLE_SIZE PAGE_SIZE
 #endif
 
 #ifndef PTE_TABLE_SIZE
 #define PTE_TABLE_SIZE PAGE_SIZE
 #endif
 void __init __weak pcpu_populate_pte(unsigned long addr)
 {
     pgd_t *pgd = pgd_offset_k(addr);
     p4d_t *p4d;
     pud_t *pud;
     pmd_t *pmd;
 
     if (pgd_none(*pgd)) {
         p4d_t *new;
 
         new = memblock_alloc(P4D_TABLE_SIZE, P4D_TABLE_SIZE);
         if (!new)
             goto err_alloc;
         pgd_populate(&init_mm, pgd, new);
     }
 
     p4d = p4d_offset(pgd, addr);
     if (p4d_none(*p4d)) {
         pud_t *new;
 
         new = memblock_alloc(PUD_TABLE_SIZE, PUD_TABLE_SIZE);
         if (!new)
             goto err_alloc;
         p4d_populate(&init_mm, p4d, new);
     }
 
     pud = pud_offset(p4d, addr);
     if (pud_none(*pud)) {
         pmd_t *new;
 
         new = memblock_alloc(PMD_TABLE_SIZE, PMD_TABLE_SIZE);
         if (!new)
             goto err_alloc;
         pud_populate(&init_mm, pud, new);
     }
 
     pmd = pmd_offset(pud, addr);
     if (!pmd_present(*pmd)) {
         pte_t *new;
 
         new = memblock_alloc(PTE_TABLE_SIZE, PTE_TABLE_SIZE);
         if (!new)
             goto err_alloc;
         pmd_populate_kernel(&init_mm, pmd, new);
     }
 
     return;
 
 err_alloc:
     panic("%s: Failed to allocate memory\n", __func__);
 }
 
 /**
  * pcpu_page_first_chunk - map the first chunk using PAGE_SIZE pages
  * @reserved_size: the size of reserved percpu area in bytes
  * @cpu_to_nd_fn: callback to convert cpu to it's node, optional
  *
  * 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_cpu_to_node_fn_t cpu_to_nd_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 = 0;
     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 = pcpu_fc_alloc(cpu, PAGE_SIZE, PAGE_SIZE, cpu_to_nd_fn);
             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_ignore_phys(__pa(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++)
             pcpu_populate_pte(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 s%zu r%zu d%zu\n",
         unit_pages, psize_str, ai->static_size,
         ai->reserved_size, ai->dyn_size);
 
     pcpu_setup_first_chunk(ai, vm.addr);
     goto out_free_ar;
 
 enomem:
     while (--j >= 0)
         pcpu_fc_free(page_address(pages[j]), PAGE_SIZE);
     rc = -ENOMEM;
 out_free_ar:
     memblock_free(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);
 
 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, NULL);
     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_ignore_phys(__pa(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;
 
     pcpu_setup_first_chunk(ai, fc);
     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);