// 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 <dennisszhou@gmail.com>
   *

   * The percpu allocator handles both static and dynamic areas.  Percpu
   * areas are allocated in chunks which are divided into units.  There is
   * a 1-to-1 mapping for units to possible cpus.  These units are grouped
   * based on NUMA properties of the machine.

   *
   *  c0                           c1                         c2
   *  -------------------          -------------------        ------------
   * | u0 | u1 | u2 | u3 |        | u0 | u1 | u2 | u3 |      | u0 | u1 | u
   *  -------------------  ......  -------------------  ....  ------------
   *

   * Allocation is done by offsets into a unit's address space.  Ie., an
   * area of 512 bytes at 6k in c1 occupies 512 bytes at 6k in c1:u0,
   * c1:u1, c1:u2, etc.  On NUMA machines, the mapping may be non-linear
   * and even sparse.  Access is handled by configuring percpu base
   * registers according to the cpu to unit mappings and offsetting the
   * base address using pcpu_unit_size.
   *
   * There is special consideration for the first chunk which must handle
   * the static percpu variables in the kernel image as allocation services

   * are not online yet.  In short, the first chunk is structured like so:

   *
   *                  <Static | [Reserved] | Dynamic>
   *
   * The static data is copied from the original section managed by the
   * linker.  The reserved section, if non-zero, primarily manages static
   * percpu variables from kernel modules.  Finally, the dynamic section
   * takes care of normal allocations.

   *

   * The allocator organizes chunks into lists according to free size and
   * tries to allocate from the fullest chunk first.  Each chunk is managed
   * by a bitmap with metadata blocks.  The allocation map is updated on
   * every allocation and free to reflect the current state while the boundary
   * map is only updated on allocation.  Each metadata block contains
   * information to help mitigate the need to iterate over large portions
   * of the bitmap.  The reverse mapping from page to chunk is stored in
   * the page's index.  Lastly, units are lazily backed and grow in unison.
   *
   * There is a unique conversion that goes on here between bytes and bits.
   * Each bit represents a fragment of size PCPU_MIN_ALLOC_SIZE.  The chunk
   * tracks the number of pages it is responsible for in nr_pages.  Helper
   * functions are used to convert from between the bytes, bits, and blocks.
   * All hints are managed in bits unless explicitly stated.

   *

   * To use this allocator, arch code should do the following:

   *

   * - define __addr_to_pcpu_ptr() and __pcpu_ptr_to_addr() to translate

   *   regular address to percpu pointer and back if they need to be
   *   different from the default

   *

   * - use pcpu_setup_first_chunk() during percpu area initialization to
   *   setup the first chunk containing the kernel static percpu area

   */

  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

  #include <linux/bitmap.h>

  #include <linux/memblock.h>

  #include <linux/err.h>

  #include <linux/lcm.h>

  #include <linux/list.h>

  #include <linux/log2.h>

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

  #include <linux/slab.h>

  #include <linux/spinlock.h>

  #include <linux/vmalloc.h>

  #include <linux/workqueue.h>

  #include <linux/kmemleak.h>

  #include <linux/sched.h>

  
  #include <asm/cacheflush.h>

  #include <asm/sections.h>

  #include <asm/tlbflush.h>

  #include <asm/io.h>

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

  #include "percpu-internal.h"

  /* the slots are sorted by free bytes left, 1-31 bytes share the same slot */
  #define PCPU_SLOT_BASE_SHIFT		5

  /* chunks in slots below this are subject to being sidelined on failed alloc */
  #define PCPU_SLOT_FAIL_THRESHOLD	3

  #define PCPU_EMPTY_POP_PAGES_LOW	2
  #define PCPU_EMPTY_POP_PAGES_HIGH	4

  #ifdef CONFIG_SMP

  /* default addr <-> pcpu_ptr mapping, override in asm/percpu.h if necessary */
  #ifndef __addr_to_pcpu_ptr
  #define __addr_to_pcpu_ptr(addr)					\

  	(void __percpu *)((unsigned long)(addr) -			\
  			  (unsigned long)pcpu_base_addr	+		\
  			  (unsigned long)__per_cpu_start)

  #endif
  #ifndef __pcpu_ptr_to_addr
  #define __pcpu_ptr_to_addr(ptr)						\

  	(void __force *)((unsigned long)(ptr) +				\
  			 (unsigned long)pcpu_base_addr -		\
  			 (unsigned long)__per_cpu_start)

  #endif

  #else	/* CONFIG_SMP */
  /* on UP, it's always identity mapped */
  #define __addr_to_pcpu_ptr(addr)	(void __percpu *)(addr)
  #define __pcpu_ptr_to_addr(ptr)		(void __force *)(ptr)
  #endif	/* CONFIG_SMP */

  static int pcpu_unit_pages __ro_after_init;
  static int pcpu_unit_size __ro_after_init;
  static int pcpu_nr_units __ro_after_init;
  static int pcpu_atom_size __ro_after_init;

  int pcpu_nr_slots __ro_after_init;

  static size_t pcpu_chunk_struct_size __ro_after_init;

  /* cpus with the lowest and highest unit addresses */

  static unsigned int pcpu_low_unit_cpu __ro_after_init;
  static unsigned int pcpu_high_unit_cpu __ro_after_init;

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

  void *pcpu_base_addr __ro_after_init;

  EXPORT_SYMBOL_GPL(pcpu_base_addr);

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

  /* group information, used for vm allocation */

  static int pcpu_nr_groups __ro_after_init;
  static const unsigned long *pcpu_group_offsets __ro_after_init;
  static const size_t *pcpu_group_sizes __ro_after_init;

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

  struct pcpu_chunk *pcpu_first_chunk __ro_after_init;

  
  /*
   * Optional reserved chunk.  This chunk reserves part of the first

   * chunk and serves it for reserved allocations.  When the reserved
   * region doesn't exist, the following variable is NULL.

   */

  struct pcpu_chunk *pcpu_reserved_chunk __ro_after_init;

  DEFINE_SPINLOCK(pcpu_lock);	/* all internal data structures */

  static DEFINE_MUTEX(pcpu_alloc_mutex);	/* chunk create/destroy, [de]pop, map ext */

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

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

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

  int pcpu_nr_empty_pop_pages;

  /*

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

   * Balance work is used to populate or destroy chunks asynchronously.  We
   * try to keep the number of populated free pages between
   * PCPU_EMPTY_POP_PAGES_LOW and HIGH for atomic allocations and at most one
   * empty chunk.
   */

  static void pcpu_balance_workfn(struct work_struct *work);
  static DECLARE_WORK(pcpu_balance_work, pcpu_balance_workfn);

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

  /**

   * pcpu_addr_in_chunk - check if the address is served from this chunk
   * @chunk: chunk of interest
   * @addr: percpu address

   *
   * RETURNS:

   * True if the address is served from this chunk.

   */

  static bool pcpu_addr_in_chunk(struct pcpu_chunk *chunk, void *addr)

  {

  	void *start_addr, *end_addr;

  	if (!chunk)

  		return false;

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

  
  	return addr >= start_addr && addr < end_addr;

  }

  static int __pcpu_size_to_slot(int size)

  {

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

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

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

  static int pcpu_chunk_slot(const struct pcpu_chunk *chunk)
  {

  	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);

  }

  static void pcpu_next_unpop(unsigned long *bitmap, int *rs, int *re, int end)

  {

  	*rs = find_next_zero_bit(bitmap, end, *rs);
  	*re = find_next_bit(bitmap, end, *rs + 1);

  }

  static void pcpu_next_pop(unsigned long *bitmap, int *rs, int *re, int end)

  {

  	*rs = find_next_bit(bitmap, end, *rs);
  	*re = find_next_zero_bit(bitmap, end, *rs + 1);

  }
  
  /*

   * Bitmap region iterators.  Iterates over the bitmap between
   * [@start, @end) in @chunk.  @rs and @re should be integer variables
   * and will be set to start and end index of the current free region.

   */

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

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

  /*
   * The following are helper functions to help access bitmaps and convert
   * between bitmap offsets to address offsets.
   */
  static unsigned long *pcpu_index_alloc_map(struct pcpu_chunk *chunk, int index)
  {
  	return chunk->alloc_map +
  	       (index * PCPU_BITMAP_BLOCK_BITS / BITS_PER_LONG);
  }
  
  static unsigned long pcpu_off_to_block_index(int off)
  {
  	return off / PCPU_BITMAP_BLOCK_BITS;
  }
  
  static unsigned long pcpu_off_to_block_off(int off)
  {
  	return off & (PCPU_BITMAP_BLOCK_BITS - 1);
  }

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

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

  /**

   * pcpu_next_md_free_region - finds the next hint free area
   * @chunk: chunk of interest
   * @bit_off: chunk offset
   * @bits: size of free area
   *
   * Helper function for pcpu_for_each_md_free_region.  It checks
   * block->contig_hint and performs aggregation across blocks to find the
   * next hint.  It modifies bit_off and bits in-place to be consumed in the
   * loop.
   */
  static void pcpu_next_md_free_region(struct pcpu_chunk *chunk, int *bit_off,
  				     int *bits)
  {
  	int i = pcpu_off_to_block_index(*bit_off);
  	int block_off = pcpu_off_to_block_off(*bit_off);
  	struct pcpu_block_md *block;
  
  	*bits = 0;
  	for (block = chunk->md_blocks + i; i < pcpu_chunk_nr_blocks(chunk);
  	     block++, i++) {
  		/* handles contig area across blocks */
  		if (*bits) {
  			*bits += block->left_free;
  			if (block->left_free == PCPU_BITMAP_BLOCK_BITS)
  				continue;
  			return;
  		}
  
  		/*
  		 * This checks three things.  First is there a contig_hint to
  		 * check.  Second, have we checked this hint before by
  		 * comparing the block_off.  Third, is this the same as the
  		 * right contig hint.  In the last case, it spills over into
  		 * the next block and should be handled by the contig area
  		 * across blocks code.
  		 */
  		*bits = block->contig_hint;
  		if (*bits && block->contig_hint_start >= block_off &&
  		    *bits + block->contig_hint_start < PCPU_BITMAP_BLOCK_BITS) {
  			*bit_off = pcpu_block_off_to_off(i,
  					block->contig_hint_start);
  			return;
  		}

  		/* reset to satisfy the second predicate above */
  		block_off = 0;

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

  /**
   * pcpu_next_fit_region - finds fit areas for a given allocation request
   * @chunk: chunk of interest
   * @alloc_bits: size of allocation
   * @align: alignment of area (max PAGE_SIZE)
   * @bit_off: chunk offset
   * @bits: size of free area
   *
   * Finds the next free region that is viable for use with a given size and
   * alignment.  This only returns if there is a valid area to be used for this
   * allocation.  block->first_free is returned if the allocation request fits
   * within the block to see if the request can be fulfilled prior to the contig
   * hint.
   */
  static void pcpu_next_fit_region(struct pcpu_chunk *chunk, int alloc_bits,
  				 int align, int *bit_off, int *bits)
  {
  	int i = pcpu_off_to_block_index(*bit_off);
  	int block_off = pcpu_off_to_block_off(*bit_off);
  	struct pcpu_block_md *block;
  
  	*bits = 0;
  	for (block = chunk->md_blocks + i; i < pcpu_chunk_nr_blocks(chunk);
  	     block++, i++) {
  		/* handles contig area across blocks */
  		if (*bits) {
  			*bits += block->left_free;
  			if (*bits >= alloc_bits)
  				return;
  			if (block->left_free == PCPU_BITMAP_BLOCK_BITS)
  				continue;
  		}
  
  		/* check block->contig_hint */
  		*bits = ALIGN(block->contig_hint_start, align) -
  			block->contig_hint_start;
  		/*
  		 * This uses the block offset to determine if this has been
  		 * checked in the prior iteration.
  		 */
  		if (block->contig_hint &&
  		    block->contig_hint_start >= block_off &&
  		    block->contig_hint >= *bits + alloc_bits) {

  			int start = pcpu_next_hint(block, alloc_bits);

  			*bits += alloc_bits + block->contig_hint_start -

  				 start;
  			*bit_off = pcpu_block_off_to_off(i, start);

  			return;
  		}

  		/* reset to satisfy the second predicate above */
  		block_off = 0;

  
  		*bit_off = ALIGN(PCPU_BITMAP_BLOCK_BITS - block->right_free,
  				 align);
  		*bits = PCPU_BITMAP_BLOCK_BITS - *bit_off;
  		*bit_off = pcpu_block_off_to_off(i, *bit_off);
  		if (*bits >= alloc_bits)
  			return;
  	}
  
  	/* no valid offsets were found - fail condition */
  	*bit_off = pcpu_chunk_map_bits(chunk);
  }

  /*
   * Metadata free area iterators.  These perform aggregation of free areas
   * based on the metadata blocks and return the offset @bit_off and size in

   * bits of the free area @bits.  pcpu_for_each_fit_region only returns when
   * a fit is found for the allocation request.

   */
  #define pcpu_for_each_md_free_region(chunk, bit_off, bits)		\
  	for (pcpu_next_md_free_region((chunk), &(bit_off), &(bits));	\
  	     (bit_off) < pcpu_chunk_map_bits((chunk));			\
  	     (bit_off) += (bits) + 1,					\
  	     pcpu_next_md_free_region((chunk), &(bit_off), &(bits)))

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

  /**

   * pcpu_mem_zalloc - allocate memory

   * @size: bytes to allocate

   * @gfp: allocation flags

   *

   * Allocate @size bytes.  If @size is smaller than PAGE_SIZE,

   * kzalloc() is used; otherwise, the equivalent of vzalloc() is used.
   * This is to facilitate passing through whitelisted flags.  The
   * returned memory is always zeroed.

   *
   * RETURNS:

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

   */

  static void *pcpu_mem_zalloc(size_t size, gfp_t gfp)

  {

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

  	if (size <= PAGE_SIZE)

  		return kzalloc(size, gfp);

  	else

  		return __vmalloc(size, gfp | __GFP_ZERO, PAGE_KERNEL);

  }

  /**
   * pcpu_mem_free - free memory
   * @ptr: memory to free

   *

   * Free @ptr.  @ptr should have been allocated using pcpu_mem_zalloc().

   */

  static void pcpu_mem_free(void *ptr)

  {

  	kvfree(ptr);

  }

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

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

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

   *
   * CONTEXT:
   * pcpu_lock.

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

  	if (oslot != nslot)
  		__pcpu_chunk_move(chunk, nslot, oslot < nslot);

  }

  /*
   * pcpu_update_empty_pages - update empty page counters

   * @chunk: chunk of interest

   * @nr: nr of empty pages

   *

   * This is used to keep track of the empty pages now based on the premise
   * a md_block covers a page.  The hint update functions recognize if a block
   * is made full or broken to calculate deltas for keeping track of free pages.

   */

  static inline void pcpu_update_empty_pages(struct pcpu_chunk *chunk, int nr)

  {

  	chunk->nr_empty_pop_pages += nr;
  	if (chunk != pcpu_reserved_chunk)
  		pcpu_nr_empty_pop_pages += nr;

  }

  /*
   * pcpu_region_overlap - determines if two regions overlap
   * @a: start of first region, inclusive
   * @b: end of first region, exclusive
   * @x: start of second region, inclusive
   * @y: end of second region, exclusive

   *

   * This is used to determine if the hint region [a, b) overlaps with the
   * allocated region [x, y).

   */

  static inline bool pcpu_region_overlap(int a, int b, int x, int y)

  {

  	return (a < y) && (x < b);

  }

  /**

   * pcpu_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);

  	int rs, re, start;	/* 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 */

  	pcpu_for_each_unpop_region(alloc_map, rs, re, start,

  				   PCPU_BITMAP_BLOCK_BITS) {
  		pcpu_block_update(block, rs, re);
  	}
  }
  
  /**
   * pcpu_block_update_hint_alloc - update hint on allocation path
   * @chunk: chunk of interest
   * @bit_off: chunk offset
   * @bits: size of request

   *
   * Updates metadata for the allocation path.  The metadata only has to be
   * refreshed by a full scan iff the chunk's contig hint is broken.  Block level
   * scans are required if the block's contig hint is broken.

   */
  static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off,
  					 int bits)
  {

  	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)
  {
  	int page_start, page_end, rs, re;

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

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

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

  }
  
  /**

   * pcpu_find_block_fit - finds the block index to start searching
   * @chunk: chunk of interest
   * @alloc_bits: size of request in allocation units
   * @align: alignment of area (max PAGE_SIZE bytes)
   * @pop_only: use populated regions only
   *

   * Given a chunk and an allocation spec, find the offset to begin searching
   * for a free region.  This iterates over the bitmap metadata blocks to
   * find an offset that will be guaranteed to fit the requirements.  It is
   * not quite first fit as if the allocation does not fit in the contig hint
   * of a block or chunk, it is skipped.  This errs on the side of caution
   * to prevent excess iteration.  Poor alignment can cause the allocator to
   * skip over blocks and chunks that have valid free areas.
   *

   * RETURNS:
   * The offset in the bitmap to begin searching.
   * -1 if no offset is found.

   */

  static int pcpu_find_block_fit(struct pcpu_chunk *chunk, int alloc_bits,
  			       size_t align, bool pop_only)

  {

  	struct pcpu_block_md *chunk_md = &chunk->chunk_md;

  	int bit_off, bits, next_off;

  	/*
  	 * Check to see if the allocation can fit in the chunk's contig hint.
  	 * This is an optimization to prevent scanning by assuming if it
  	 * cannot fit in the global hint, there is memory pressure and creating
  	 * a new chunk would happen soon.
  	 */

  	bit_off = ALIGN(chunk_md->contig_hint_start, align) -
  		  chunk_md->contig_hint_start;
  	if (bit_off + alloc_bits > chunk_md->contig_hint)

  		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.

   */

  static void pcpu_free_area(struct pcpu_chunk *chunk, int off)

  {

  	struct pcpu_block_md *chunk_md = &chunk->chunk_md;

  	int bit_off, bits, end, oslot;

  	lockdep_assert_held(&pcpu_lock);

  	pcpu_stats_area_dealloc(chunk);

  	oslot = pcpu_chunk_slot(chunk);

  	bit_off = off / PCPU_MIN_ALLOC_SIZE;

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

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

  	/* update first free bit */

  	chunk_md->first_free = min(chunk_md->first_free, bit_off);

  	pcpu_block_update_hint_free(chunk, bit_off, bits);

  	pcpu_chunk_relocate(chunk, oslot);
  }

  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 = sizeof(struct pcpu_chunk) +

  		BITS_TO_LONGS(region_size >> PAGE_SHIFT) * sizeof(unsigned long);

  	chunk = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
  	if (!chunk)
  		panic("%s: Failed to allocate %zu bytes
  ", __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
  ", __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
  ", __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
  ", __func__,
  		      alloc_size);

  	pcpu_init_md_blocks(chunk);

  
  	/* manage populated page bitmap */
  	chunk->immutable = true;

  	bitmap_fill(chunk->populated, chunk->nr_pages);
  	chunk->nr_populated = chunk->nr_pages;

  	chunk->nr_empty_pop_pages = chunk->nr_pages;

  	chunk->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;
  
  	pcpu_init_md_blocks(chunk);

  	/* init metadata */

  	chunk->free_bytes = chunk->nr_pages * PAGE_SIZE;

  	return chunk;

  md_blocks_fail:
  	pcpu_mem_free(chunk->bound_map);

  bound_map_fail:
  	pcpu_mem_free(chunk->alloc_map);
  alloc_map_fail:
  	pcpu_mem_free(chunk);
  
  	return NULL;

  }
  
  static void pcpu_free_chunk(struct pcpu_chunk *chunk)
  {
  	if (!chunk)
  		return;

  	pcpu_mem_free(chunk->md_blocks);

  	pcpu_mem_free(chunk->bound_map);
  	pcpu_mem_free(chunk->alloc_map);

  	pcpu_mem_free(chunk);

  }

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

   *
   * If this is @for_alloc, do not increment pcpu_nr_empty_pop_pages because it
   * is to serve an allocation in that area.

   */

  static void pcpu_chunk_populated(struct pcpu_chunk *chunk, int page_start,

  				 int page_end)

  {
  	int nr = page_end - page_start;
  
  	lockdep_assert_held(&pcpu_lock);
  
  	bitmap_set(chunk->populated, page_start, nr);
  	chunk->nr_populated += nr;

  	pcpu_nr_populated += nr;

  	pcpu_update_empty_pages(chunk, nr);

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

  	pcpu_nr_populated -= nr;

  
  	pcpu_update_empty_pages(chunk, -nr);

  }

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

   */

  static int pcpu_populate_chunk(struct pcpu_chunk *chunk,

  			       int page_start, int page_end, gfp_t gfp);

  static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
  				  int page_start, int page_end);

  static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp);

  static void pcpu_destroy_chunk(struct pcpu_chunk *chunk);
  static struct page *pcpu_addr_to_page(void *addr);
  static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai);

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

  #include "percpu-vm.c"

  #endif

  
  /**

   * pcpu_chunk_addr_search - determine chunk containing specified address
   * @addr: address for which the chunk needs to be determined.
   *

   * This is an internal function that handles all but static allocations.
   * Static percpu address values should never be passed into the allocator.
   *

   * RETURNS:
   * The address of the found chunk.
   */
  static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
  {

  	/* is it in the dynamic region (first chunk)? */

  	if (pcpu_addr_in_chunk(pcpu_first_chunk, addr))

  		return pcpu_first_chunk;

  
  	/* is it in the reserved region? */

  	if (pcpu_addr_in_chunk(pcpu_reserved_chunk, addr))

  		return pcpu_reserved_chunk;

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

  	return pcpu_get_page_chunk(pcpu_addr_to_page(addr));

  }
  
  /**

   * pcpu_alloc - the percpu allocator

   * @size: size of area to allocate in bytes

   * @align: alignment of area (max PAGE_SIZE)

   * @reserved: allocate from the reserved chunk if available

   * @gfp: allocation flags

   *

   * Allocate percpu area of @size bytes aligned at @align.  If @gfp doesn't

   * contain %GFP_KERNEL, the allocation is atomic. If @gfp has __GFP_NOWARN
   * then no warning will be triggered on invalid or failed allocation
   * requests.

   *
   * RETURNS:
   * Percpu pointer to the allocated area on success, NULL on failure.
   */

  static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
  				 gfp_t gfp)

  {

  	/* whitelisted flags that can be passed to the backing allocators */
  	gfp_t pcpu_gfp = gfp & (GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN);

  	bool is_atomic = (gfp & GFP_KERNEL) != GFP_KERNEL;
  	bool do_warn = !(gfp & __GFP_NOWARN);

  	static int warn_limit = 10;

  	struct pcpu_chunk *chunk, *next;

  	const char *err;

  	int slot, off, cpu, ret;

  	unsigned long flags;

  	void __percpu *ptr;

  	size_t bits, bit_align;

  	/*

  	 * There is now a minimum allocation size of PCPU_MIN_ALLOC_SIZE,
  	 * therefore alignment must be a minimum of that many bytes.
  	 * An allocation may have internal fragmentation from rounding up
  	 * of up to PCPU_MIN_ALLOC_SIZE - 1 bytes.

  	 */

  	if (unlikely(align < PCPU_MIN_ALLOC_SIZE))
  		align = PCPU_MIN_ALLOC_SIZE;

  	size = ALIGN(size, PCPU_MIN_ALLOC_SIZE);

  	bits = size >> PCPU_MIN_ALLOC_SHIFT;
  	bit_align = align >> PCPU_MIN_ALLOC_SHIFT;

  	if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE ||
  		     !is_power_of_2(align))) {

  		WARN(do_warn, "illegal size (%zu) or align (%zu) for percpu allocation
  ",

  		     size, align);

  		return NULL;
  	}

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

  	spin_lock_irqsave(&pcpu_lock, flags);

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

  		off = pcpu_find_block_fit(chunk, bits, bit_align, is_atomic);
  		if (off < 0) {

  			err = "alloc from reserved chunk failed";

  			goto fail_unlock;

  		}

  		off = pcpu_alloc_area(chunk, bits, bit_align, off);

  		if (off >= 0)
  			goto area_found;

  		err = "alloc from reserved chunk failed";

  		goto fail_unlock;

  	}

  restart:

  	/* search through normal chunks */

  	for (slot = pcpu_size_to_slot(size); slot < pcpu_nr_slots; slot++) {

  		list_for_each_entry_safe(chunk, next, &pcpu_slot[slot], list) {

  			off = pcpu_find_block_fit(chunk, bits, bit_align,
  						  is_atomic);

  			if (off < 0) {
  				if (slot < PCPU_SLOT_FAIL_THRESHOLD)
  					pcpu_chunk_move(chunk, 0);

  				continue;

  			}

  			off = pcpu_alloc_area(chunk, bits, bit_align, off);

  			if (off >= 0)
  				goto area_found;

  		}
  	}

  	spin_unlock_irqrestore(&pcpu_lock, flags);

  	/*
  	 * No space left.  Create a new chunk.  We don't want multiple
  	 * tasks to create chunks simultaneously.  Serialize and create iff
  	 * there's still no empty chunk after grabbing the mutex.
  	 */

  	if (is_atomic) {
  		err = "atomic alloc failed, no space left";

  		goto fail;

  	}

  	if (list_empty(&pcpu_slot[pcpu_nr_slots - 1])) {

  		chunk = pcpu_create_chunk(pcpu_gfp);

  		if (!chunk) {
  			err = "failed to allocate new chunk";
  			goto fail;
  		}
  
  		spin_lock_irqsave(&pcpu_lock, flags);
  		pcpu_chunk_relocate(chunk, -1);
  	} else {
  		spin_lock_irqsave(&pcpu_lock, flags);

  	}

  	goto restart;

  
  area_found:

  	pcpu_stats_area_alloc(chunk, size);

  	spin_unlock_irqrestore(&pcpu_lock, flags);

  	/* populate if not all pages are already there */

  	if (!is_atomic) {

  		int page_start, page_end, rs, re;

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

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

  			WARN_ON(chunk->immutable);

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

  
  			spin_lock_irqsave(&pcpu_lock, flags);
  			if (ret) {

  				pcpu_free_area(chunk, off);

  				err = "failed to populate";
  				goto fail_unlock;
  			}

  			pcpu_chunk_populated(chunk, rs, re);

  			spin_unlock_irqrestore(&pcpu_lock, flags);

  		}

  		mutex_unlock(&pcpu_alloc_mutex);
  	}

  	if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW)
  		pcpu_schedule_balance_work();

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

  	ptr = __addr_to_pcpu_ptr(chunk->base_addr + off);

  	kmemleak_alloc_percpu(ptr, size, gfp);

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

  	return ptr;

  
  fail_unlock:

  	spin_unlock_irqrestore(&pcpu_lock, flags);

  fail:

  	trace_percpu_alloc_percpu_fail(reserved, is_atomic, size, align);

  	if (!is_atomic && do_warn && warn_limit) {

  		pr_warn("allocation failed, size=%zu align=%zu atomic=%d, %s
  ",

  			size, align, is_atomic, err);

  		dump_stack();
  		if (!--warn_limit)

  			pr_info("limit reached, disable warning
  ");

  	}

  	if (is_atomic) {
  		/* see the flag handling in pcpu_blance_workfn() */
  		pcpu_atomic_alloc_failed = true;
  		pcpu_schedule_balance_work();

  	} else {
  		mutex_unlock(&pcpu_alloc_mutex);

  	}

  	return NULL;

  }

  
  /**

   * __alloc_percpu_gfp - allocate dynamic percpu area

   * @size: size of area to allocate in bytes
   * @align: alignment of area (max PAGE_SIZE)

   * @gfp: allocation flags

   *

   * Allocate zero-filled percpu area of @size bytes aligned at @align.  If
   * @gfp doesn't contain %GFP_KERNEL, the allocation doesn't block and can

   * be called from any context but is a lot more likely to fail. If @gfp
   * has __GFP_NOWARN then no warning will be triggered on invalid or failed
   * allocation requests.

   *

   * RETURNS:
   * Percpu pointer to the allocated area on success, NULL on failure.
   */

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

  void __percpu *__alloc_percpu(size_t size, size_t align)

  {

  	return pcpu_alloc(size, align, false, GFP_KERNEL);

  }

  EXPORT_SYMBOL_GPL(__alloc_percpu);

  /**
   * __alloc_reserved_percpu - allocate reserved percpu area
   * @size: size of area to allocate in bytes
   * @align: alignment of area (max PAGE_SIZE)
   *

   * Allocate zero-filled percpu area of @size bytes aligned at @align
   * from reserved percpu area if arch has set it up; otherwise,
   * allocation is served from the same dynamic area.  Might sleep.
   * Might trigger writeouts.

   *

   * CONTEXT:
   * Does GFP_KERNEL allocation.
   *

   * RETURNS:
   * Percpu pointer to the allocated area on success, NULL on failure.
   */

  void __percpu *__alloc_reserved_percpu(size_t size, size_t align)

  {

  	return pcpu_alloc(size, align, true, GFP_KERNEL);

  }