/*

   * mm/percpu.c - percpu memory allocator

   *
   * Copyright (C) 2009		SUSE Linux Products GmbH
   * Copyright (C) 2009		Tejun Heo <tj@kernel.org>
   *
   * This file is released under the GPLv2.
   *
   * This is percpu allocator which can handle both static and dynamic

   * areas.  Percpu areas are allocated in chunks.  Each chunk is
   * consisted of boot-time determined number of units and the first
   * chunk is used for static percpu variables in the kernel image

   * (special boot time alloc/init handling necessary as these areas
   * need to be brought up before allocation services are running).
   * Unit grows as necessary and all units grow or shrink in unison.

   * When a chunk is filled up, another chunk is allocated.

   *
   *  c0                           c1                         c2
   *  -------------------          -------------------        ------------
   * | u0 | u1 | u2 | u3 |        | u0 | u1 | u2 | u3 |      | u0 | u1 | u
   *  -------------------  ......  -------------------  ....  ------------
   *
   * Allocation is done in offset-size areas of single unit space.  Ie,
   * an area of 512 bytes at 6k in c1 occupies 512 bytes at 6k of c1:u0,

   * c1:u1, c1:u2 and c1:u3.  On UMA, units corresponds directly to
   * cpus.  On NUMA, the mapping can be non-linear and even sparse.
   * Percpu access can be done by configuring percpu base registers
   * according to cpu to unit mapping and pcpu_unit_size.

   *

   * There are usually many small percpu allocations many of them being
   * as small as 4 bytes.  The allocator organizes chunks into lists

   * according to free size and tries to allocate from the fullest one.
   * Each chunk keeps the maximum contiguous area size hint which is
   * guaranteed to be eqaul to or larger than the maximum contiguous
   * area in the chunk.  This helps the allocator not to iterate the
   * chunk maps unnecessarily.
   *
   * Allocation state in each chunk is kept using an array of integers
   * on chunk->map.  A positive value in the map represents a free
   * region and negative allocated.  Allocation inside a chunk is done
   * by scanning this map sequentially and serving the first matching
   * entry.  This is mostly copied from the percpu_modalloc() allocator.

   * Chunks can be determined from the address using the index field
   * in the page struct. The index field contains a pointer to the chunk.

   *
   * To use this allocator, arch code should do the followings.
   *

   * - 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

   */
  
  #include <linux/bitmap.h>
  #include <linux/bootmem.h>

  #include <linux/err.h>

  #include <linux/list.h>

  #include <linux/log2.h>

  #include <linux/mm.h>
  #include <linux/module.h>
  #include <linux/mutex.h>
  #include <linux/percpu.h>
  #include <linux/pfn.h>

  #include <linux/slab.h>

  #include <linux/spinlock.h>

  #include <linux/vmalloc.h>

  #include <linux/workqueue.h>

  
  #include <asm/cacheflush.h>

  #include <asm/sections.h>

  #include <asm/tlbflush.h>

  #include <asm/io.h>

  #define PCPU_SLOT_BASE_SHIFT		5	/* 1-31 shares the same slot */
  #define PCPU_DFL_MAP_ALLOC		16	/* start a map with 16 ents */

  /* 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

  struct pcpu_chunk {
  	struct list_head	list;		/* linked to pcpu_slot lists */

  	int			free_size;	/* free bytes in the chunk */
  	int			contig_hint;	/* max contiguous size hint */

  	void			*base_addr;	/* base address of this chunk */

  	int			map_used;	/* # of map entries used */
  	int			map_alloc;	/* # of map entries allocated */
  	int			*map;		/* allocation map */

  	void			*data;		/* chunk data */

  	bool			immutable;	/* no [de]population allowed */

  	unsigned long		populated[];	/* populated bitmap */

  };

  static int pcpu_unit_pages __read_mostly;
  static int pcpu_unit_size __read_mostly;

  static int pcpu_nr_units __read_mostly;

  static int pcpu_atom_size __read_mostly;

  static int pcpu_nr_slots __read_mostly;
  static size_t pcpu_chunk_struct_size __read_mostly;

  /* cpus with the lowest and highest unit numbers */
  static unsigned int pcpu_first_unit_cpu __read_mostly;
  static unsigned int pcpu_last_unit_cpu __read_mostly;

  /* the address of the first chunk which starts with the kernel static area */

  void *pcpu_base_addr __read_mostly;

  EXPORT_SYMBOL_GPL(pcpu_base_addr);

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

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

  /*
   * 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.
   */
  static struct pcpu_chunk *pcpu_first_chunk;
  
  /*
   * Optional reserved chunk.  This chunk reserves part of the first
   * chunk and serves it for reserved allocations.  The amount of
   * reserved offset is in pcpu_reserved_chunk_limit.  When reserved
   * area doesn't exist, the following variables contain NULL and 0
   * respectively.
   */

  static struct pcpu_chunk *pcpu_reserved_chunk;

  static int pcpu_reserved_chunk_limit;

  /*

   * Synchronization rules.
   *
   * There are two locks - pcpu_alloc_mutex and pcpu_lock.  The former

   * protects allocation/reclaim paths, chunks, populated bitmap and
   * vmalloc mapping.  The latter is a spinlock and protects the index
   * data structures - chunk slots, chunks and area maps in chunks.

   *
   * During allocation, pcpu_alloc_mutex is kept locked all the time and
   * pcpu_lock is grabbed and released as necessary.  All actual memory

   * allocations are done using GFP_KERNEL with pcpu_lock released.  In
   * general, percpu memory can't be allocated with irq off but
   * irqsave/restore are still used in alloc path so that it can be used
   * from early init path - sched_init() specifically.

   *
   * Free path accesses and alters only the index data structures, so it
   * can be safely called from atomic context.  When memory needs to be
   * returned to the system, free path schedules reclaim_work which
   * grabs both pcpu_alloc_mutex and pcpu_lock, unlinks chunks to be
   * reclaimed, release both locks and frees the chunks.  Note that it's
   * necessary to grab both locks to remove a chunk from circulation as
   * allocation path might be referencing the chunk with only
   * pcpu_alloc_mutex locked.

   */

  static DEFINE_MUTEX(pcpu_alloc_mutex);	/* protects whole alloc and reclaim */
  static DEFINE_SPINLOCK(pcpu_lock);	/* protects index data structures */

  static struct list_head *pcpu_slot __read_mostly; /* chunk list slots */

  /* reclaim work to release fully free chunks, scheduled from free path */
  static void pcpu_reclaim(struct work_struct *work);
  static DECLARE_WORK(pcpu_reclaim_work, pcpu_reclaim);

  static bool pcpu_addr_in_first_chunk(void *addr)
  {
  	void *first_start = pcpu_first_chunk->base_addr;
  
  	return addr >= first_start && addr < first_start + pcpu_unit_size;
  }
  
  static bool pcpu_addr_in_reserved_chunk(void *addr)
  {
  	void *first_start = pcpu_first_chunk->base_addr;
  
  	return addr >= first_start &&
  		addr < first_start + pcpu_reserved_chunk_limit;
  }

  static int __pcpu_size_to_slot(int size)

  {

  	int highbit = fls(size);	/* size is in bytes */

  	return max(highbit - PCPU_SLOT_BASE_SHIFT + 2, 1);
  }

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

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

  /* set the pointer to a chunk in a page struct */
  static void pcpu_set_page_chunk(struct page *page, struct pcpu_chunk *pcpu)
  {
  	page->index = (unsigned long)pcpu;
  }
  
  /* obtain pointer to a chunk from a page struct */
  static struct pcpu_chunk *pcpu_get_page_chunk(struct page *page)
  {
  	return (struct pcpu_chunk *)page->index;
  }
  
  static int __maybe_unused pcpu_page_idx(unsigned int cpu, int page_idx)

  {

  	return pcpu_unit_map[cpu] * pcpu_unit_pages + page_idx;

  }

  static unsigned long pcpu_chunk_addr(struct pcpu_chunk *chunk,
  				     unsigned int cpu, int page_idx)

  {

  	return (unsigned long)chunk->base_addr + pcpu_unit_offsets[cpu] +

  		(page_idx << PAGE_SHIFT);

  }

  static void __maybe_unused pcpu_next_unpop(struct pcpu_chunk *chunk,
  					   int *rs, int *re, int end)

  {
  	*rs = find_next_zero_bit(chunk->populated, end, *rs);
  	*re = find_next_bit(chunk->populated, end, *rs + 1);
  }

  static void __maybe_unused pcpu_next_pop(struct pcpu_chunk *chunk,
  					 int *rs, int *re, int end)

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

  /**

   * pcpu_mem_alloc - allocate memory
   * @size: bytes to allocate

   *

   * Allocate @size bytes.  If @size is smaller than PAGE_SIZE,
   * kzalloc() is used; otherwise, vmalloc() is used.  The returned
   * memory is always zeroed.

   *

   * CONTEXT:
   * Does GFP_KERNEL allocation.
   *

   * RETURNS:

   * Pointer to the allocated area on success, NULL on failure.

   */

  static void *pcpu_mem_alloc(size_t size)

  {

  	if (WARN_ON_ONCE(!slab_is_available()))
  		return NULL;

  	if (size <= PAGE_SIZE)
  		return kzalloc(size, GFP_KERNEL);
  	else {
  		void *ptr = vmalloc(size);
  		if (ptr)
  			memset(ptr, 0, size);
  		return ptr;
  	}
  }

  /**
   * pcpu_mem_free - free memory
   * @ptr: memory to free
   * @size: size of the area
   *
   * Free @ptr.  @ptr should have been allocated using pcpu_mem_alloc().
   */
  static void pcpu_mem_free(void *ptr, size_t size)
  {

  	if (size <= PAGE_SIZE)

  		kfree(ptr);

  	else

  		vfree(ptr);

  }
  
  /**
   * pcpu_chunk_relocate - put chunk in the appropriate chunk slot
   * @chunk: chunk of interest
   * @oslot: the previous slot it was on
   *
   * This function is called after an allocation or free changed @chunk.
   * New slot according to the changed state is determined and @chunk is

   * moved to the slot.  Note that the reserved chunk is never put on
   * chunk slots.

   *
   * CONTEXT:
   * pcpu_lock.

   */
  static void pcpu_chunk_relocate(struct pcpu_chunk *chunk, int oslot)
  {
  	int nslot = pcpu_chunk_slot(chunk);

  	if (chunk != pcpu_reserved_chunk && oslot != nslot) {

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

  /**

   * pcpu_need_to_extend - determine whether chunk area map needs to be extended
   * @chunk: chunk of interest

   *

   * Determine whether area map of @chunk needs to be extended to
   * accomodate a new allocation.

   *

   * CONTEXT:

   * pcpu_lock.

   *

   * RETURNS:

   * New target map allocation length if extension is necessary, 0
   * otherwise.

   */

  static int pcpu_need_to_extend(struct pcpu_chunk *chunk)

  {
  	int new_alloc;

  	if (chunk->map_alloc >= chunk->map_used + 2)
  		return 0;
  
  	new_alloc = PCPU_DFL_MAP_ALLOC;
  	while (new_alloc < chunk->map_used + 2)
  		new_alloc *= 2;

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

  		return -ENOMEM;

  	/* acquire pcpu_lock and switch to new area map */
  	spin_lock_irqsave(&pcpu_lock, flags);
  
  	if (new_alloc <= chunk->map_alloc)
  		goto out_unlock;

  	old_size = chunk->map_alloc * sizeof(chunk->map[0]);
  	memcpy(new, chunk->map, old_size);

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

  	new = NULL;
  
  out_unlock:
  	spin_unlock_irqrestore(&pcpu_lock, flags);
  
  	/*
  	 * pcpu_mem_free() might end up calling vfree() which uses
  	 * IRQ-unsafe lock and thus can't be called under pcpu_lock.
  	 */
  	pcpu_mem_free(old, old_size);
  	pcpu_mem_free(new, new_size);

  	return 0;
  }
  
  /**

   * pcpu_split_block - split a map block
   * @chunk: chunk of interest
   * @i: index of map block to split

   * @head: head size in bytes (can be 0)
   * @tail: tail size in bytes (can be 0)

   *
   * Split the @i'th map block into two or three blocks.  If @head is
   * non-zero, @head bytes block is inserted before block @i moving it
   * to @i+1 and reducing its size by @head bytes.
   *
   * If @tail is non-zero, the target block, which can be @i or @i+1
   * depending on @head, is reduced by @tail bytes and @tail byte block
   * is inserted after the target block.
   *

   * @chunk->map must have enough free slots to accomodate the split.

   *
   * CONTEXT:
   * pcpu_lock.

   */

  static void pcpu_split_block(struct pcpu_chunk *chunk, int i,
  			     int head, int tail)

  {
  	int nr_extra = !!head + !!tail;

  	BUG_ON(chunk->map_alloc < chunk->map_used + nr_extra);

  	/* insert new subblocks */

  	memmove(&chunk->map[i + nr_extra], &chunk->map[i],
  		sizeof(chunk->map[0]) * (chunk->map_used - i));
  	chunk->map_used += nr_extra;
  
  	if (head) {
  		chunk->map[i + 1] = chunk->map[i] - head;
  		chunk->map[i++] = head;
  	}
  	if (tail) {
  		chunk->map[i++] -= tail;
  		chunk->map[i] = tail;
  	}

  }
  
  /**
   * pcpu_alloc_area - allocate area from a pcpu_chunk
   * @chunk: chunk of interest

   * @size: wanted size in bytes

   * @align: wanted align
   *
   * Try to allocate @size bytes area aligned at @align from @chunk.
   * Note that this function only allocates the offset.  It doesn't
   * populate or map the area.
   *

   * @chunk->map must have at least two free slots.
   *

   * CONTEXT:
   * pcpu_lock.
   *

   * RETURNS:

   * Allocated offset in @chunk on success, -1 if no matching area is
   * found.

   */
  static int pcpu_alloc_area(struct pcpu_chunk *chunk, int size, int align)
  {
  	int oslot = pcpu_chunk_slot(chunk);
  	int max_contig = 0;
  	int i, off;

  	for (i = 0, off = 0; i < chunk->map_used; off += abs(chunk->map[i++])) {
  		bool is_last = i + 1 == chunk->map_used;
  		int head, tail;
  
  		/* extra for alignment requirement */
  		head = ALIGN(off, align) - off;
  		BUG_ON(i == 0 && head != 0);
  
  		if (chunk->map[i] < 0)
  			continue;
  		if (chunk->map[i] < head + size) {
  			max_contig = max(chunk->map[i], max_contig);
  			continue;
  		}
  
  		/*
  		 * If head is small or the previous block is free,
  		 * merge'em.  Note that 'small' is defined as smaller
  		 * than sizeof(int), which is very small but isn't too
  		 * uncommon for percpu allocations.
  		 */
  		if (head && (head < sizeof(int) || chunk->map[i - 1] > 0)) {
  			if (chunk->map[i - 1] > 0)
  				chunk->map[i - 1] += head;
  			else {
  				chunk->map[i - 1] -= head;
  				chunk->free_size -= head;
  			}
  			chunk->map[i] -= head;
  			off += head;
  			head = 0;
  		}
  
  		/* if tail is small, just keep it around */
  		tail = chunk->map[i] - head - size;
  		if (tail < sizeof(int))
  			tail = 0;
  
  		/* split if warranted */
  		if (head || tail) {

  			pcpu_split_block(chunk, i, head, tail);

  			if (head) {
  				i++;
  				off += head;
  				max_contig = max(chunk->map[i - 1], max_contig);
  			}
  			if (tail)
  				max_contig = max(chunk->map[i + 1], max_contig);
  		}
  
  		/* update hint and mark allocated */
  		if (is_last)
  			chunk->contig_hint = max_contig; /* fully scanned */
  		else
  			chunk->contig_hint = max(chunk->contig_hint,
  						 max_contig);
  
  		chunk->free_size -= chunk->map[i];
  		chunk->map[i] = -chunk->map[i];
  
  		pcpu_chunk_relocate(chunk, oslot);
  		return off;
  	}
  
  	chunk->contig_hint = max_contig;	/* fully scanned */
  	pcpu_chunk_relocate(chunk, oslot);

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

  }
  
  /**
   * pcpu_free_area - free area to a pcpu_chunk
   * @chunk: chunk of interest
   * @freeme: offset of area to free
   *
   * Free area starting from @freeme to @chunk.  Note that this function
   * only modifies the allocation map.  It doesn't depopulate or unmap
   * the area.

   *
   * CONTEXT:
   * pcpu_lock.

   */
  static void pcpu_free_area(struct pcpu_chunk *chunk, int freeme)
  {
  	int oslot = pcpu_chunk_slot(chunk);
  	int i, off;
  
  	for (i = 0, off = 0; i < chunk->map_used; off += abs(chunk->map[i++]))
  		if (off == freeme)
  			break;
  	BUG_ON(off != freeme);
  	BUG_ON(chunk->map[i] > 0);
  
  	chunk->map[i] = -chunk->map[i];
  	chunk->free_size += chunk->map[i];
  
  	/* merge with previous? */
  	if (i > 0 && chunk->map[i - 1] >= 0) {
  		chunk->map[i - 1] += chunk->map[i];
  		chunk->map_used--;
  		memmove(&chunk->map[i], &chunk->map[i + 1],
  			(chunk->map_used - i) * sizeof(chunk->map[0]));
  		i--;
  	}
  	/* merge with next? */
  	if (i + 1 < chunk->map_used && chunk->map[i + 1] >= 0) {
  		chunk->map[i] += chunk->map[i + 1];
  		chunk->map_used--;
  		memmove(&chunk->map[i + 1], &chunk->map[i + 2],
  			(chunk->map_used - (i + 1)) * sizeof(chunk->map[0]));
  	}
  
  	chunk->contig_hint = max(chunk->map[i], chunk->contig_hint);
  	pcpu_chunk_relocate(chunk, oslot);
  }

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

  	chunk = pcpu_mem_alloc(pcpu_chunk_struct_size);

  	if (!chunk)
  		return NULL;
  
  	chunk->map = pcpu_mem_alloc(PCPU_DFL_MAP_ALLOC * sizeof(chunk->map[0]));
  	if (!chunk->map) {
  		kfree(chunk);
  		return NULL;
  	}
  
  	chunk->map_alloc = PCPU_DFL_MAP_ALLOC;
  	chunk->map[chunk->map_used++] = pcpu_unit_size;
  
  	INIT_LIST_HEAD(&chunk->list);
  	chunk->free_size = pcpu_unit_size;
  	chunk->contig_hint = pcpu_unit_size;
  
  	return chunk;
  }
  
  static void pcpu_free_chunk(struct pcpu_chunk *chunk)
  {
  	if (!chunk)
  		return;
  	pcpu_mem_free(chunk->map, chunk->map_alloc * sizeof(chunk->map[0]));
  	kfree(chunk);
  }

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

   */

  static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size);
  static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk, int off, int size);
  static struct pcpu_chunk *pcpu_create_chunk(void);
  static void pcpu_destroy_chunk(struct pcpu_chunk *chunk);
  static struct page *pcpu_addr_to_page(void *addr);
  static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai);

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

  #include "percpu-vm.c"

  #endif

  
  /**

   * pcpu_chunk_addr_search - determine chunk containing specified address
   * @addr: address for which the chunk needs to be determined.
   *
   * RETURNS:
   * The address of the found chunk.
   */
  static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
  {
  	/* is it in the first chunk? */
  	if (pcpu_addr_in_first_chunk(addr)) {
  		/* is it in the reserved area? */
  		if (pcpu_addr_in_reserved_chunk(addr))
  			return pcpu_reserved_chunk;
  		return pcpu_first_chunk;
  	}
  
  	/*
  	 * The address is relative to unit0 which might be unused and
  	 * thus unmapped.  Offset the address to the unit space of the
  	 * current processor before looking it up in the vmalloc
  	 * space.  Note that any possible cpu id can be used here, so
  	 * there's no need to worry about preemption or cpu hotplug.
  	 */
  	addr += pcpu_unit_offsets[raw_smp_processor_id()];

  	return pcpu_get_page_chunk(pcpu_addr_to_page(addr));

  }
  
  /**

   * pcpu_alloc - the percpu allocator

   * @size: size of area to allocate in bytes

   * @align: alignment of area (max PAGE_SIZE)

   * @reserved: allocate from the reserved chunk if available

   *

   * Allocate percpu area of @size bytes aligned at @align.
   *
   * CONTEXT:
   * Does GFP_KERNEL allocation.

   *
   * 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)

  {

  	static int warn_limit = 10;

  	struct pcpu_chunk *chunk;

  	const char *err;

  	int slot, off, new_alloc;

  	unsigned long flags;

  	if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE)) {

  		WARN(true, "illegal size (%zu) or align (%zu) for "
  		     "percpu allocation
  ", size, align);
  		return NULL;
  	}

  	mutex_lock(&pcpu_alloc_mutex);

  	spin_lock_irqsave(&pcpu_lock, flags);

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

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

  			goto fail_unlock;

  		}

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

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

  		err = "alloc from reserved chunk failed";

  		goto fail_unlock;

  	}

  restart:

  	/* search through normal chunks */

  	for (slot = pcpu_size_to_slot(size); slot < pcpu_nr_slots; slot++) {
  		list_for_each_entry(chunk, &pcpu_slot[slot], list) {
  			if (size > chunk->contig_hint)
  				continue;

  			new_alloc = pcpu_need_to_extend(chunk);
  			if (new_alloc) {
  				spin_unlock_irqrestore(&pcpu_lock, flags);
  				if (pcpu_extend_area_map(chunk,
  							 new_alloc) < 0) {
  					err = "failed to extend area map";
  					goto fail_unlock_mutex;
  				}
  				spin_lock_irqsave(&pcpu_lock, flags);
  				/*
  				 * pcpu_lock has been dropped, need to
  				 * restart cpu_slot list walking.
  				 */
  				goto restart;

  			}

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

  		}
  	}
  
  	/* hmmm... no space left, create a new chunk */

  	spin_unlock_irqrestore(&pcpu_lock, flags);

  	chunk = pcpu_create_chunk();

  	if (!chunk) {
  		err = "failed to allocate new chunk";

  		goto fail_unlock_mutex;

  	}

  	spin_lock_irqsave(&pcpu_lock, flags);

  	pcpu_chunk_relocate(chunk, -1);

  	goto restart;

  
  area_found:

  	spin_unlock_irqrestore(&pcpu_lock, flags);

  	/* populate, map and clear the area */
  	if (pcpu_populate_chunk(chunk, off, size)) {

  		spin_lock_irqsave(&pcpu_lock, flags);

  		pcpu_free_area(chunk, off);

  		err = "failed to populate";

  		goto fail_unlock;

  	}

  	mutex_unlock(&pcpu_alloc_mutex);

  	/* return address relative to base address */
  	return __addr_to_pcpu_ptr(chunk->base_addr + off);

  
  fail_unlock:

  	spin_unlock_irqrestore(&pcpu_lock, flags);

  fail_unlock_mutex:
  	mutex_unlock(&pcpu_alloc_mutex);

  	if (warn_limit) {
  		pr_warning("PERCPU: allocation failed, size=%zu align=%zu, "
  			   "%s
  ", size, align, err);
  		dump_stack();
  		if (!--warn_limit)
  			pr_info("PERCPU: limit reached, disable warning
  ");
  	}

  	return NULL;

  }

  
  /**
   * __alloc_percpu - allocate dynamic percpu area
   * @size: size of area to allocate in bytes
   * @align: alignment of area (max PAGE_SIZE)
   *
   * Allocate percpu area of @size bytes aligned at @align.  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_percpu(size_t size, size_t align)

  {
  	return pcpu_alloc(size, align, false);
  }

  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 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);
  }

  /**
   * pcpu_reclaim - reclaim fully free chunks, workqueue function
   * @work: unused
   *
   * Reclaim all fully free chunks except for the first one.

   *
   * CONTEXT:
   * workqueue context.

   */
  static void pcpu_reclaim(struct work_struct *work)

  {

  	LIST_HEAD(todo);
  	struct list_head *head = &pcpu_slot[pcpu_nr_slots - 1];
  	struct pcpu_chunk *chunk, *next;

  	mutex_lock(&pcpu_alloc_mutex);
  	spin_lock_irq(&pcpu_lock);

  
  	list_for_each_entry_safe(chunk, next, head, list) {
  		WARN_ON(chunk->immutable);
  
  		/* spare the first one */
  		if (chunk == list_first_entry(head, struct pcpu_chunk, list))
  			continue;

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

  	spin_unlock_irq(&pcpu_lock);

  
  	list_for_each_entry_safe(chunk, next, &todo, list) {

  		pcpu_depopulate_chunk(chunk, 0, pcpu_unit_size);

  		pcpu_destroy_chunk(chunk);

  	}

  
  	mutex_unlock(&pcpu_alloc_mutex);

  }
  
  /**
   * free_percpu - free percpu area
   * @ptr: pointer to area to free
   *

   * Free percpu area @ptr.
   *
   * CONTEXT:
   * Can be called from atomic context.

   */

  void free_percpu(void __percpu *ptr)

  {

  	void *addr;

  	struct pcpu_chunk *chunk;

  	unsigned long flags;

  	int off;
  
  	if (!ptr)
  		return;

  	addr = __pcpu_ptr_to_addr(ptr);

  	spin_lock_irqsave(&pcpu_lock, flags);

  
  	chunk = pcpu_chunk_addr_search(addr);

  	off = addr - chunk->base_addr;

  
  	pcpu_free_area(chunk, off);

  	/* if there are more than one fully free chunks, wake up grim reaper */

  	if (chunk->free_size == pcpu_unit_size) {
  		struct pcpu_chunk *pos;

  		list_for_each_entry(pos, &pcpu_slot[pcpu_nr_slots - 1], list)

  			if (pos != chunk) {

  				schedule_work(&pcpu_reclaim_work);

  				break;
  			}
  	}

  	spin_unlock_irqrestore(&pcpu_lock, flags);

  }
  EXPORT_SYMBOL_GPL(free_percpu);

  /**

   * 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)
  {
  	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);
  
  		if ((void *)addr >= start && (void *)addr < start + static_size)
  			return true;
          }
  	return false;
  }
  
  /**

   * 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.
   *
   * 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_start, first_end;
  	unsigned int cpu;
  
  	/*
  	 * The following test on first_start/end isn't strictly
  	 * necessary but will speed up lookups of addresses which
  	 * aren't in the first chunk.
  	 */
  	first_start = pcpu_chunk_addr(pcpu_first_chunk, pcpu_first_unit_cpu, 0);
  	first_end = pcpu_chunk_addr(pcpu_first_chunk, pcpu_last_unit_cpu,
  				    pcpu_unit_pages);
  	if ((unsigned long)addr >= first_start &&
  	    (unsigned long)addr < first_end) {
  		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 ((unsigned long)addr < VMALLOC_START ||
  		    (unsigned long)addr >= VMALLOC_END)
  			return __pa(addr);
  		else
  			return page_to_phys(vmalloc_to_page(addr));
  	} else

  		return page_to_phys(pcpu_addr_to_page(addr));

  }

  /**

   * pcpu_alloc_alloc_info - allocate percpu allocation info
   * @nr_groups: the number of groups
   * @nr_units: the number of units
   *
   * Allocate ai which is large enough for @nr_groups groups containing
   * @nr_units units.  The returned ai's groups[0].cpu_map points to the
   * cpu_map array which is long enough for @nr_units and filled with
   * NR_CPUS.  It's the caller's responsibility to initialize cpu_map
   * pointer of other groups.
   *
   * RETURNS:
   * Pointer to the allocated pcpu_alloc_info on success, NULL on
   * failure.
   */
  struct pcpu_alloc_info * __init pcpu_alloc_alloc_info(int nr_groups,
  						      int nr_units)
  {
  	struct pcpu_alloc_info *ai;
  	size_t base_size, ai_size;
  	void *ptr;
  	int unit;
  
  	base_size = ALIGN(sizeof(*ai) + nr_groups * sizeof(ai->groups[0]),
  			  __alignof__(ai->groups[0].cpu_map[0]));
  	ai_size = base_size + nr_units * sizeof(ai->groups[0].cpu_map[0]);
  
  	ptr = alloc_bootmem_nopanic(PFN_ALIGN(ai_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)
  {
  	free_bootmem(__pa(ai), ai->__ai_size);
  }
  
  /**
   * 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 mutliples of atom size and CPUs which are of
   * LOCAL_DISTANCE both ways are grouped together and share space for
   * units in the same group.  The returned configuration is guaranteed
   * to have CPUs on different nodes on different groups and >=75% usage
   * of allocated virtual address space.

   *
   * RETURNS:

   * On success, pointer to the new allocation_info is returned.  On
   * failure, ERR_PTR value is returned.

   */

  static struct pcpu_alloc_info * __init pcpu_build_alloc_info(
  				size_t reserved_size, size_t dyn_size,

  				size_t atom_size,
  				pcpu_fc_cpu_distance_fn_t cpu_distance_fn)

  {
  	static int group_map[NR_CPUS] __initdata;
  	static int group_cnt[NR_CPUS] __initdata;
  	const size_t static_size = __per_cpu_end - __per_cpu_start;

  	int nr_groups = 1, nr_units = 0;

  	size_t size_sum, min_unit_size, alloc_size;
  	int upa, max_upa, uninitialized_var(best_upa);	/* units_per_alloc */

  	int last_allocs, group, unit;

  	unsigned int cpu, tcpu;

  	struct pcpu_alloc_info *ai;
  	unsigned int *cpu_map;

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

  	memset(group_cnt, 0, sizeof(group_cnt));

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

  	dyn_size = size_sum - static_size - reserved_size;

  	/*
  	 * Determine min_unit_size, alloc_size and max_upa such that

  	 * alloc_size is multiple of atom_size and is the smallest

  	 * which can accomodate 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);

  	alloc_size = roundup(min_unit_size, atom_size);

  	upa = alloc_size / min_unit_size;
  	while (alloc_size % upa || ((alloc_size / upa) & ~PAGE_MASK))
  		upa--;
  	max_upa = upa;
  
  	/* group cpus according to their proximity */
  	for_each_possible_cpu(cpu) {
  		group = 0;
  	next_group:
  		for_each_possible_cpu(tcpu) {
  			if (cpu == tcpu)
  				break;

  			if (group_map[tcpu] == group && cpu_distance_fn &&

  			    (cpu_distance_fn(cpu, tcpu) > LOCAL_DISTANCE ||
  			     cpu_distance_fn(tcpu, cpu) > LOCAL_DISTANCE)) {
  				group++;

  				nr_groups = max(nr_groups, group + 1);

  				goto next_group;
  			}
  		}
  		group_map[cpu] = group;
  		group_cnt[group]++;

  	}
  
  	/*
  	 * Expand unit size until address space usage goes over 75%
  	 * and then as much as possible without using more address
  	 * space.
  	 */
  	last_allocs = INT_MAX;
  	for (upa = max_upa; upa; upa--) {
  		int allocs = 0, wasted = 0;
  
  		if (alloc_size % upa || ((alloc_size / upa) & ~PAGE_MASK))
  			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 25%.  The
  		 * greater-than comparison ensures upa==1 always
  		 * passes the following check.
  		 */
  		if (wasted > num_possible_cpus() / 3)
  			continue;
  
  		/* and then don't consume more memory */
  		if (allocs > last_allocs)
  			break;
  		last_allocs = allocs;
  		best_upa = upa;
  	}

  	upa = best_upa;
  
  	/* allocate and fill alloc_info */
  	for (group = 0; group < nr_groups; group++)
  		nr_units += roundup(group_cnt[group], upa);
  
  	ai = pcpu_alloc_alloc_info(nr_groups, nr_units);
  	if (!ai)
  		return ERR_PTR(-ENOMEM);
  	cpu_map = ai->groups[0].cpu_map;
  
  	for (group = 0; group < nr_groups; group++) {
  		ai->groups[group].cpu_map = cpu_map;
  		cpu_map += roundup(group_cnt[group], upa);
  	}
  
  	ai->static_size = static_size;
  	ai->reserved_size = reserved_size;
  	ai->dyn_size = dyn_size;
  	ai->unit_size = alloc_size / upa;
  	ai->atom_size = atom_size;
  	ai->alloc_size = alloc_size;
  
  	for (group = 0, unit = 0; group_cnt[group]; 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;

  }

  /**
   * 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)) {

  				printk("
  ");

  				printk("%spcpu-alloc: ", lvl);
  			}
  			printk("[%0*d] ", group_width, group);
  
  			for (unit_end += upa; unit < unit_end; unit++)
  				if (gi->cpu_map[unit] != NR_CPUS)
  					printk("%0*d ", cpu_width,
  					       gi->cpu_map[unit]);
  				else
  					printk("%s ", empty_str);

  		}

  	}
  	printk("
  ");
  }

  /**

   * pcpu_setup_first_chunk - initialize the first percpu chunk

   * @ai: pcpu_alloc_info describing how to percpu area is shaped

   * @base_addr: mapped address

   *
   * Initialize the first percpu chunk which contains the kernel static
   * perpcu area.  This function is to be called from arch percpu area

   * setup path.

   *

   * @ai contains all information necessary to initialize the first
   * chunk and prime the dynamic percpu allocator.
   *
   * @ai->static_size is the size of static percpu area.
   *
   * @ai->reserved_size, if non-zero, specifies the amount of bytes to

   * reserve after the static area in the first chunk.  This reserves
   * the first chunk such that it's available only through reserved
   * percpu allocation.  This is primarily used to serve module percpu
   * static areas on architectures where the addressing model has
   * limited offset range for symbol relocations to guarantee module
   * percpu symbols fall inside the relocatable range.
   *

   * @ai->dyn_size determines the number of bytes available for dynamic
   * allocation in the first chunk.  The area between @ai->static_size +
   * @ai->reserved_size + @ai->dyn_size and @ai->unit_size is unused.

   *

   * @ai->unit_size specifies unit size and must be aligned to PAGE_SIZE
   * and equal to or larger than @ai->static_size + @ai->reserved_size +
   * @ai->dyn_size.

   *

   * @ai->atom_size is the allocation atom size and used as alignment
   * for vm areas.

   *

   * @ai->alloc_size is the allocation size and always multiple of
   * @ai->atom_size.  This is larger than @ai->atom_size if
   * @ai->unit_size is larger than @ai->atom_size.
   *
   * @ai->nr_groups and @ai->groups describe virtual memory layout of
   * percpu areas.  Units which should be colocated are put into the
   * same group.  Dynamic VM areas will be allocated according to these
   * groupings.  If @ai->nr_groups is zero, a single group containing
   * all units is assumed.

   *

   * The caller should have mapped the first chunk at @base_addr and
   * copied static data to each unit.

   *

   * If the first chunk ends up with both reserved and dynamic areas, it
   * is served by two chunks - one to serve the core static and reserved
   * areas and the other for the dynamic area.  They share the same vm
   * and page map but uses different area allocation map to stay away
   * from each other.  The latter chunk is circulated in the chunk slots
   * and available for dynamic allocation like any other chunks.
   *

   * RETURNS:

   * 0 on success, -errno on failure.

   */

  int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
  				  void *base_addr)

  {

  	static char cpus_buf[4096] __initdata;

  	static int smap[PERCPU_DYNAMIC_EARLY_SLOTS] __initdata;
  	static int dmap[PERCPU_DYNAMIC_EARLY_SLOTS] __initdata;

  	size_t dyn_size = ai->dyn_size;
  	size_t size_sum = ai->static_size + ai->reserved_size + dyn_size;

  	struct pcpu_chunk *schunk, *dchunk = NULL;

  	unsigned long *group_offsets;
  	size_t *group_sizes;

  	unsigned long *unit_off;

  	unsigned int cpu;

  	int *unit_map;
  	int group, unit, i;

  	cpumask_scnprintf(cpus_buf, sizeof(cpus_buf), cpu_possible_mask);
  
  #define PCPU_SETUP_BUG_ON(cond)	do {					\
  	if (unlikely(cond)) {						\
  		pr_emerg("PERCPU: failed to initialize, %s", #cond);	\
  		pr_emerg("PERCPU: cpu_possible_mask=%s
  ", cpus_buf);	\
  		pcpu_dump_alloc_info(KERN_EMERG, ai);			\
  		BUG();							\
  	}								\
  } while (0)

  	/* sanity checks */

  	PCPU_SETUP_BUG_ON(ai->nr_groups <= 0);
  	PCPU_SETUP_BUG_ON(!ai->static_size);
  	PCPU_SETUP_BUG_ON(!base_addr);
  	PCPU_SETUP_BUG_ON(ai->unit_size < size_sum);
  	PCPU_SETUP_BUG_ON(ai->unit_size & ~PAGE_MASK);
  	PCPU_SETUP_BUG_ON(ai->unit_size < PCPU_MIN_UNIT_SIZE);

  	PCPU_SETUP_BUG_ON(ai->dyn_size < PERCPU_DYNAMIC_EARLY_SIZE);

  	PCPU_SETUP_BUG_ON(pcpu_verify_alloc_info(ai) < 0);

  	/* process group information and build config tables accordingly */
  	group_offsets = alloc_bootmem(ai->nr_groups * sizeof(group_offsets[0]));
  	group_sizes = alloc_bootmem(ai->nr_groups * sizeof(group_sizes[0]));

  	unit_map = alloc_bootmem(nr_cpu_ids * sizeof(unit_map[0]));

  	unit_off = alloc_bootmem(nr_cpu_ids * sizeof(unit_off[0]));

  	for (cpu = 0; cpu < nr_cpu_ids; cpu++)

  		unit_map[cpu] = UINT_MAX;

  	pcpu_first_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;

  			if (pcpu_first_unit_cpu == NR_CPUS)
  				pcpu_first_unit_cpu = cpu;
  		}

  	}

  	pcpu_last_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_INFO, ai);

  	pcpu_nr_groups = ai->nr_groups;
  	pcpu_group_offsets = group_offsets;
  	pcpu_group_sizes = group_sizes;

  	pcpu_unit_map = unit_map;

  	pcpu_unit_offsets = unit_off;

  
  	/* determine basic parameters */

  	pcpu_unit_pages = ai->unit_size >> PAGE_SHIFT;

  	pcpu_unit_size = pcpu_unit_pages << PAGE_SHIFT;

  	pcpu_atom_size = ai->atom_size;

  	pcpu_chunk_struct_size = sizeof(struct pcpu_chunk) +
  		BITS_TO_LONGS(pcpu_unit_pages) * sizeof(unsigned long);

  	/*
  	 * Allocate chunk slots.  The additional last slot is for
  	 * empty chunks.
  	 */
  	pcpu_nr_slots = __pcpu_size_to_slot(pcpu_unit_size) + 2;

  	pcpu_slot = alloc_bootmem(pcpu_nr_slots * sizeof(pcpu_slot[0]));
  	for (i = 0; i < pcpu_nr_slots; i++)
  		INIT_LIST_HEAD(&pcpu_slot[i]);

  	/*
  	 * Initialize static chunk.  If reserved_size is zero, the
  	 * static chunk covers static area + dynamic allocation area
  	 * in the first chunk.  If reserved_size is not zero, it
  	 * covers static area + reserved area (mostly used for module
  	 * static percpu allocation).
  	 */

  	schunk = alloc_bootmem(pcpu_chunk_struct_size);
  	INIT_LIST_HEAD(&schunk->list);

  	schunk->base_addr = base_addr;

  	schunk->map = smap;
  	schunk->map_alloc = ARRAY_SIZE(smap);

  	schunk->immutable = true;

  	bitmap_fill(schunk->populated, pcpu_unit_pages);

  	if (ai->reserved_size) {
  		schunk->free_size = ai->reserved_size;

  		pcpu_reserved_chunk = schunk;

  		pcpu_reserved_chunk_limit = ai->static_size + ai->reserved_size;

  	} else {
  		schunk->free_size = dyn_size;
  		dyn_size = 0;			/* dynamic area covered */
  	}

  	schunk->contig_hint = schunk->free_size;

  	schunk->map[schunk->map_used++] = -ai->static_size;

  	if (schunk->free_size)
  		schunk->map[schunk->map_used++] = schunk->free_size;

  	/* init dynamic chunk if necessary */
  	if (dyn_size) {

  		dchunk = alloc_bootmem(pcpu_chunk_struct_size);

  		INIT_LIST_HEAD(&dchunk->list);

  		dchunk->base_addr = base_addr;

  		dchunk->map = dmap;
  		dchunk->map_alloc = ARRAY_SIZE(dmap);

  		dchunk->immutable = true;

  		bitmap_fill(dchunk->populated, pcpu_unit_pages);

  
  		dchunk->contig_hint = dchunk->free_size = dyn_size;
  		dchunk->map[dchunk->map_used++] = -pcpu_reserved_chunk_limit;
  		dchunk->map[dchunk->map_used++] = dchunk->free_size;
  	}

  	/* link the first chunk in */

  	pcpu_first_chunk = dchunk ?: schunk;
  	pcpu_chunk_relocate(pcpu_first_chunk, -1);

  
  	/* we're done */

  	pcpu_base_addr = base_addr;

  	return 0;

  }

  const char *pcpu_fc_names[PCPU_FC_NR] __initdata = {
  	[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 (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_warning("PERCPU: unknown allocator %s specified
  ", str);

  	return 0;

  }

  early_param("percpu_alloc", percpu_alloc_setup);

  #if defined(CONFIG_NEED_PER_CPU_EMBED_FIRST_CHUNK) || \
  	!defined(CONFIG_HAVE_SETUP_PER_CPU_AREA)

  /**
   * pcpu_embed_first_chunk - embed the first percpu chunk into bootmem

   * @reserved_size: the size of reserved percpu area in bytes

   * @dyn_size: minimum free size for dynamic allocation in bytes

   * @atom_size: allocation atom size
   * @cpu_distance_fn: callback to determine distance between cpus, optional
   * @alloc_fn: function to allocate percpu page
   * @free_fn: funtion to free percpu page

   *
   * This is a helper to ease setting up embedded first percpu chunk and
   * can be called where pcpu_setup_first_chunk() is expected.
   *
   * If this function is used to setup the first chunk, it is allocated

   * by calling @alloc_fn and used as-is without being mapped into
   * vmalloc area.  Allocations are always whole multiples of @atom_size
   * aligned to @atom_size.
   *
   * This enables the first chunk to piggy back on the linear physical
   * mapping which often uses larger page size.  Please note that this
   * can result in very sparse cpu->unit mapping on NUMA machines thus
   * requiring large vmalloc address space.  Don't use this allocator if
   * vmalloc space is not orders of magnitude larger than distances
   * between node memory addresses (ie. 32bit NUMA machines).

   *

   * @dyn_size specifies the minimum dynamic area size.

   *
   * If the needed size is smaller than the minimum or specified unit

   * size, the leftover is returned using @free_fn.

   *
   * RETURNS:

   * 0 on success, -errno on failure.

   */

  int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,

  				  size_t atom_size,
  				  pcpu_fc_cpu_distance_fn_t cpu_distance_fn,
  				  pcpu_fc_alloc_fn_t alloc_fn,
  				  pcpu_fc_free_fn_t free_fn)

  {

  	void *base = (void *)ULONG_MAX;
  	void **areas = NULL;

  	struct pcpu_alloc_info *ai;

  	size_t size_sum, areas_size, max_distance;

  	int group, i, rc;

  	ai = pcpu_build_alloc_info(reserved_size, dyn_size, atom_size,
  				   cpu_distance_fn);

  	if (IS_ERR(ai))
  		return PTR_ERR(ai);

  	size_sum = ai->static_size + ai->reserved_size + ai->dyn_size;

  	areas_size = PFN_ALIGN(ai->nr_groups * sizeof(void *));

  	areas = alloc_bootmem_nopanic(areas_size);
  	if (!areas) {

  		rc = -ENOMEM;

  		goto out_free;

  	}

  	/* allocate, copy and determine base address */
  	for (group = 0; group < ai->nr_groups; group++) {
  		struct pcpu_group_info *gi = &ai->groups[group];
  		unsigned int cpu = NR_CPUS;
  		void *ptr;
  
  		for (i = 0; i < gi->nr_units && cpu == NR_CPUS; i++)
  			cpu = gi->cpu_map[i];
  		BUG_ON(cpu == NR_CPUS);
  
  		/* allocate space for the whole group */
  		ptr = alloc_fn(cpu, gi->nr_units * ai->unit_size, atom_size);
  		if (!ptr) {
  			rc = -ENOMEM;
  			goto out_free_areas;
  		}
  		areas[group] = ptr;

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

  	}

  	/* base address is now known, determine group base offsets */

  	max_distance = 0;
  	for (group = 0; group < ai->nr_groups; group++) {

  		ai->groups[group].base_offset = areas[group] - base;

  		max_distance = max_t(size_t, max_distance,
  				     ai->groups[group].base_offset);

  	}
  	max_distance += ai->unit_size;
  
  	/* warn if maximum distance is further than 75% of vmalloc space */
  	if (max_distance > (VMALLOC_END - VMALLOC_START) * 3 / 4) {

  		pr_warning("PERCPU: max_distance=0x%zx too large for vmalloc "

  			   "space 0x%lx
  ",
  			   max_distance, VMALLOC_END - VMALLOC_START);
  #ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
  		/* and fail if we have fallback */
  		rc = -EINVAL;
  		goto out_free;
  #endif
  	}

  	pr_info("PERCPU: Embedded %zu pages/cpu @%p s%zu r%zu d%zu u%zu
  ",

  		PFN_DOWN(size_sum), base, ai->static_size, ai->reserved_size,
  		ai->dyn_size, ai->unit_size);

  	rc = pcpu_setup_first_chunk(ai, base);

  	goto out_free;
  
  out_free_areas:
  	for (group = 0; group < ai->nr_groups; group++)
  		free_fn(areas[group],
  			ai->groups[group].nr_units * ai->unit_size);
  out_free:

  	pcpu_free_alloc_info(ai);

  	if (areas)
  		free_bootmem(__pa(areas), areas_size);

  	return rc;

  }

  #endif /* CONFIG_NEED_PER_CPU_EMBED_FIRST_CHUNK ||
  	  !CONFIG_HAVE_SETUP_PER_CPU_AREA */

  #ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK

  /**

   * pcpu_page_first_chunk - map the first chunk using PAGE_SIZE pages

   * @reserved_size: the size of reserved percpu area in bytes
   * @alloc_fn: function to allocate percpu page, always called with PAGE_SIZE
   * @free_fn: funtion to free percpu page, always called with PAGE_SIZE
   * @populate_pte_fn: function to populate pte
   *

   * This is a helper to ease setting up page-remapped first percpu
   * chunk and can be called where pcpu_setup_first_chunk() is expected.

   *
   * This is the basic allocator.  Static percpu area is allocated
   * page-by-page into vmalloc area.
   *
   * RETURNS:

   * 0 on success, -errno on failure.

   */

  int __init pcpu_page_first_chunk(size_t reserved_size,
  				 pcpu_fc_alloc_fn_t alloc_fn,
  				 pcpu_fc_free_fn_t free_fn,
  				 pcpu_fc_populate_pte_fn_t populate_pte_fn)

  {

  	static struct vm_struct vm;

  	struct pcpu_alloc_info *ai;

  	char psize_str[16];

  	int unit_pages;

  	size_t pages_size;

  	struct page **pages;

  	int unit, i, j, rc;

  	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);
  	BUG_ON(ai->groups[0].nr_units != num_possible_cpus());
  
  	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 = alloc_bootmem(pages_size);

  	/* allocate pages */

  	j = 0;

  	for (unit = 0; unit < num_possible_cpus(); unit++)

  		for (i = 0; i < unit_pages; i++) {

  			unsigned int cpu = ai->groups[0].cpu_map[unit];

  			void *ptr;

  			ptr = alloc_fn(cpu, PAGE_SIZE, PAGE_SIZE);

  			if (!ptr) {

  				pr_warning("PERCPU: failed to allocate %s page "
  					   "for cpu%u
  ", psize_str, cpu);

  				goto enomem;
  			}

  			pages[j++] = virt_to_page(ptr);

  		}

  	/* allocate vm area, map the pages and copy static data */
  	vm.flags = VM_ALLOC;

  	vm.size = num_possible_cpus() * ai->unit_size;

  	vm_area_register_early(&vm, PAGE_SIZE);

  	for (unit = 0; unit < num_possible_cpus(); unit++) {

  		unsigned long unit_addr =

  			(unsigned long)vm.addr + unit * ai->unit_size;

  		for (i = 0; i < unit_pages; i++)

  			populate_pte_fn(unit_addr + (i << PAGE_SHIFT));
  
  		/* pte already populated, the following shouldn't fail */

  		rc = __pcpu_map_pages(unit_addr, &pages[unit * unit_pages],
  				      unit_pages);
  		if (rc < 0)
  			panic("failed to map percpu area, err=%d
  ", 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("PERCPU: %d %s pages/cpu @%p s%zu r%zu d%zu
  ",

  		unit_pages, psize_str, vm.addr, ai->static_size,
  		ai->reserved_size, ai->dyn_size);

  	rc = pcpu_setup_first_chunk(ai, vm.addr);

  	goto out_free_ar;
  
  enomem:
  	while (--j >= 0)

  		free_fn(page_address(pages[j]), PAGE_SIZE);

  	rc = -ENOMEM;

  out_free_ar:

  	free_bootmem(__pa(pages), pages_size);

  	pcpu_free_alloc_info(ai);

  	return rc;

  }

  #endif /* CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK */

  /*

   * Generic 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.
   */
  #ifndef CONFIG_HAVE_SETUP_PER_CPU_AREA
  unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
  EXPORT_SYMBOL(__per_cpu_offset);

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

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

  void __init setup_per_cpu_areas(void)
  {

  	unsigned long delta;
  	unsigned int cpu;

  	int rc;

  
  	/*
  	 * Always reserve area for module percpu variables.  That's
  	 * what the legacy allocator did.
  	 */

  	rc = pcpu_embed_first_chunk(PERCPU_MODULE_RESERVE,

  				    PERCPU_DYNAMIC_RESERVE, PAGE_SIZE, NULL,
  				    pcpu_dfl_fc_alloc, pcpu_dfl_fc_free);

  	if (rc < 0)

  		panic("Failed to initialized 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 */

  
  /*
   * First and reserved chunks are initialized with temporary allocation
   * map in initdata so that they can be used before slab is online.
   * This function is called after slab is brought up and replaces those
   * with properly allocated maps.
   */
  void __init percpu_init_late(void)
  {
  	struct pcpu_chunk *target_chunks[] =
  		{ pcpu_first_chunk, pcpu_reserved_chunk, NULL };
  	struct pcpu_chunk *chunk;
  	unsigned long flags;
  	int i;
  
  	for (i = 0; (chunk = target_chunks[i]); i++) {
  		int *map;
  		const size_t size = PERCPU_DYNAMIC_EARLY_SLOTS * sizeof(map[0]);
  
  		BUILD_BUG_ON(size > PAGE_SIZE);
  
  		map = pcpu_mem_alloc(size);
  		BUG_ON(!map);
  
  		spin_lock_irqsave(&pcpu_lock, flags);
  		memcpy(map, chunk->map, size);
  		chunk->map = map;
  		spin_unlock_irqrestore(&pcpu_lock, flags);
  	}
  }