Merge branch 'for-4.14' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu

Pull percpu updates from Tejun Heo:
 "A lot of changes for percpu this time around. percpu inherited the
  same area allocator from the original pre-virtual-address-mapped
  implementation. This was from the time when percpu allocator wasn't
  used all that much and the implementation was focused on simplicity,
  with the unfortunate computational complexity of O(number of areas
  allocated from the chunk) per alloc / free.

  With the increase in percpu usage, we're hitting cases where the lack
  of scalability is hurting. The most prominent one right now is bpf
  perpcu map creation / destruction which may allocate and free a lot of
  entries consecutively and it's likely that the problem will become
  more prominent in the future.

  To address the issue, Dennis replaced the area allocator with hinted
  bitmap allocator which is more consistent. While the new allocator
  does perform a bit worse in some cases, it outperforms the old
  allocator way more than an order of magnitude in other more common
  scenarios while staying mostly flat in CPU overhead and completely
  flat in memory consumption"

* 'for-4.14' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu: (27 commits)
  percpu: update header to contain bitmap allocator explanation.
  percpu: update pcpu_find_block_fit to use an iterator
  percpu: use metadata blocks to update the chunk contig hint
  percpu: update free path to take advantage of contig hints
  percpu: update alloc path to only scan if contig hints are broken
  percpu: keep track of the best offset for contig hints
  percpu: skip chunks if the alloc does not fit in the contig hint
  percpu: add first_bit to keep track of the first free in the bitmap
  percpu: introduce bitmap metadata blocks
  percpu: replace area map allocator with bitmap
  percpu: generalize bitmap (un)populated iterators
  percpu: increase minimum percpu allocation size and align first regions
  percpu: introduce nr_empty_pop_pages to help empty page accounting
  percpu: change the number of pages marked in the first_chunk pop bitmap
  percpu: combine percpu address checks
  percpu: modify base_addr to be region specific
  percpu: setup_first_chunk rename schunk/dchunk to chunk
  percpu: end chunk area maps page aligned for the populated bitmap
  percpu: unify allocation of schunk and dchunk
  percpu: setup_first_chunk remove dyn_size and consolidate logic
  ...

include/linux/percpu.h

@@ -21,6 +21,25 @@
 /* minimum unit size, also is the maximum supported allocation size */
 #define PCPU_MIN_UNIT_SIZE		PFN_ALIGN(32 << 10)
 
+/* minimum allocation size and shift in bytes */
+#define PCPU_MIN_ALLOC_SHIFT		2
+#define PCPU_MIN_ALLOC_SIZE		(1 << PCPU_MIN_ALLOC_SHIFT)
+
+/* number of bits per page, used to trigger a scan if blocks are > PAGE_SIZE */
+#define PCPU_BITS_PER_PAGE		(PAGE_SIZE >> PCPU_MIN_ALLOC_SHIFT)
+
+/*
+ * This determines the size of each metadata block.  There are several subtle
+ * constraints around this constant.  The reserved region must be a multiple of
+ * PCPU_BITMAP_BLOCK_SIZE.  Additionally, PCPU_BITMAP_BLOCK_SIZE must be a
+ * multiple of PAGE_SIZE or PAGE_SIZE must be a multiple of
+ * PCPU_BITMAP_BLOCK_SIZE to align with the populated page map. The unit_size
+ * also has to be a multiple of PCPU_BITMAP_BLOCK_SIZE to ensure full blocks.
+ */
+#define PCPU_BITMAP_BLOCK_SIZE		PAGE_SIZE
+#define PCPU_BITMAP_BLOCK_BITS		(PCPU_BITMAP_BLOCK_SIZE >>	\
+					 PCPU_MIN_ALLOC_SHIFT)
+
 /*
  * Percpu allocator can serve percpu allocations before slab is
  * initialized which allows slab to depend on the percpu allocator.
@@ -116,7 +135,6 @@ extern bool is_kernel_percpu_address(unsigned long addr);
 #if !defined(CONFIG_SMP) || !defined(CONFIG_HAVE_SETUP_PER_CPU_AREA)
 extern void __init setup_per_cpu_areas(void);
 #endif
-extern void __init percpu_init_late(void);
 
 extern void __percpu *__alloc_percpu_gfp(size_t size, size_t align, gfp_t gfp);
 extern void __percpu *__alloc_percpu(size_t size, size_t align);

init/main.c

@@ -501,7 +501,6 @@ static void __init mm_init(void)
 	page_ext_init_flatmem();
 	mem_init();
 	kmem_cache_init();
-	percpu_init_late();
 	pgtable_init();
 	vmalloc_init();
 	ioremap_huge_init();

mm/percpu-internal.h

@@ -4,6 +4,22 @@
 #include <linux/types.h>
 #include <linux/percpu.h>
 
+/*
+ * pcpu_block_md is the metadata block struct.
+ * Each chunk's bitmap is split into a number of full blocks.
+ * All units are in terms of bits.
+ */
+struct pcpu_block_md {
+	int                     contig_hint;    /* contig hint for block */
+	int                     contig_hint_start; /* block relative starting
+						      position of the contig hint */
+	int                     left_free;      /* size of free space along
+						   the left side of the block */
+	int                     right_free;     /* size of free space along
+						   the right side of the block */
+	int                     first_free;     /* block position of first free */
+};
+
 struct pcpu_chunk {
 #ifdef CONFIG_PERCPU_STATS
 	int			nr_alloc;	/* # of allocations */
@@ -11,24 +27,29 @@ struct pcpu_chunk {
 #endif
 
 	struct list_head	list;		/* linked to pcpu_slot lists */
-	int			free_size;	/* free bytes in the chunk */
-	int			contig_hint;	/* max contiguous size hint */
+	int			free_bytes;	/* free bytes in the chunk */
+	int			contig_bits;	/* max contiguous size hint */
+	int			contig_bits_start; /* contig_bits starting
+						      offset */
 	void			*base_addr;	/* base address of this chunk */
 
-	int			map_used;	/* # of map entries used before the sentry */
-	int			map_alloc;	/* # of map entries allocated */
-	int			*map;		/* allocation map */
-	struct list_head	map_extend_list;/* on pcpu_map_extend_chunks */
+	unsigned long		*alloc_map;	/* allocation map */
+	unsigned long		*bound_map;	/* boundary map */
+	struct pcpu_block_md	*md_blocks;	/* metadata blocks */
 
 	void			*data;		/* chunk data */
-	int			first_free;	/* no free below this */
+	int			first_bit;	/* no free below this */
 	bool			immutable;	/* no [de]population allowed */
-	bool			has_reserved;	/* Indicates if chunk has reserved space
-						   at the beginning. Reserved chunk will
-						   contain reservation for static chunk.
-						   Dynamic chunk will contain reservation
-						   for static and reserved chunks. */
+	int			start_offset;	/* the overlap with the previous
+						   region to have a page aligned
+						   base_addr */
+	int			end_offset;	/* additional area required to
+						   have the region end page
+						   aligned */
+
+	int			nr_pages;	/* # of pages served by this chunk */
 	int			nr_populated;	/* # of populated pages */
+	int                     nr_empty_pop_pages; /* # of empty populated pages */
 	unsigned long		populated[];	/* populated bitmap */
 };
 
@@ -36,10 +57,47 @@ extern spinlock_t pcpu_lock;
 
 extern struct list_head *pcpu_slot;
 extern int pcpu_nr_slots;
+extern int pcpu_nr_empty_pop_pages;
 
 extern struct pcpu_chunk *pcpu_first_chunk;
 extern struct pcpu_chunk *pcpu_reserved_chunk;
 
+/**
+ * pcpu_chunk_nr_blocks - converts nr_pages to # of md_blocks
+ * @chunk: chunk of interest
+ *
+ * This conversion is from the number of physical pages that the chunk
+ * serves to the number of bitmap blocks used.
+ */
+static inline int pcpu_chunk_nr_blocks(struct pcpu_chunk *chunk)
+{
+	return chunk->nr_pages * PAGE_SIZE / PCPU_BITMAP_BLOCK_SIZE;
+}
+
+/**
+ * pcpu_nr_pages_to_map_bits - converts the pages to size of bitmap
+ * @pages: number of physical pages
+ *
+ * This conversion is from physical pages to the number of bits
+ * required in the bitmap.
+ */
+static inline int pcpu_nr_pages_to_map_bits(int pages)
+{
+	return pages * PAGE_SIZE / PCPU_MIN_ALLOC_SIZE;
+}
+
+/**
+ * pcpu_chunk_map_bits - helper to convert nr_pages to size of bitmap
+ * @chunk: chunk of interest
+ *
+ * This conversion is from the number of physical pages that the chunk
+ * serves to the number of bits in the bitmap.
+ */
+static inline int pcpu_chunk_map_bits(struct pcpu_chunk *chunk)
+{
+	return pcpu_nr_pages_to_map_bits(chunk->nr_pages);
+}
+
 #ifdef CONFIG_PERCPU_STATS
 
 #include <linux/spinlock.h>

mm/percpu-km.c

@@ -69,7 +69,7 @@ static struct pcpu_chunk *pcpu_create_chunk(void)
 	chunk->base_addr = page_address(pages) - pcpu_group_offsets[0];
 
 	spin_lock_irq(&pcpu_lock);
-	pcpu_chunk_populated(chunk, 0, nr_pages);
+	pcpu_chunk_populated(chunk, 0, nr_pages, false);
 	spin_unlock_irq(&pcpu_lock);
 
 	pcpu_stats_chunk_alloc();

mm/percpu-stats.c

@@ -18,7 +18,7 @@
 #include "percpu-internal.h"
 
 #define P(X, Y) \
-	seq_printf(m, "  %-24s: %8lld\n", X, (long long int)Y)
+	seq_printf(m, "  %-20s: %12lld\n", X, (long long int)Y)
 
 struct percpu_stats pcpu_stats;
 struct pcpu_alloc_info pcpu_stats_ai;
@@ -29,64 +29,85 @@ static int cmpint(const void *a, const void *b)
 }
 
 /*
- * Iterates over all chunks to find the max # of map entries used.
+ * Iterates over all chunks to find the max nr_alloc entries.
  */
-static int find_max_map_used(void)
+static int find_max_nr_alloc(void)
 {
 	struct pcpu_chunk *chunk;
-	int slot, max_map_used;
+	int slot, max_nr_alloc;
 
-	max_map_used = 0;
+	max_nr_alloc = 0;
 	for (slot = 0; slot < pcpu_nr_slots; slot++)
 		list_for_each_entry(chunk, &pcpu_slot[slot], list)
-			max_map_used = max(max_map_used, chunk->map_used);
+			max_nr_alloc = max(max_nr_alloc, chunk->nr_alloc);
 
-	return max_map_used;
+	return max_nr_alloc;
 }
 
 /*
  * Prints out chunk state. Fragmentation is considered between
  * the beginning of the chunk to the last allocation.
+ *
+ * All statistics are in bytes unless stated otherwise.
  */
 static void chunk_map_stats(struct seq_file *m, struct pcpu_chunk *chunk,
-			    void *buffer)
+			    int *buffer)
 {
-	int i, s_index, last_alloc, alloc_sign, as_len;
+	int i, last_alloc, as_len, start, end;
 	int *alloc_sizes, *p;
 	/* statistics */
 	int sum_frag = 0, max_frag = 0;
 	int cur_min_alloc = 0, cur_med_alloc = 0, cur_max_alloc = 0;
 
 	alloc_sizes = buffer;
-	s_index = chunk->has_reserved ? 1 : 0;
-
-	/* find last allocation */
-	last_alloc = -1;
-	for (i = chunk->map_used - 1; i >= s_index; i--) {
-		if (chunk->map[i] & 1) {
-			last_alloc = i;
-			break;
-		}
-	}
 
-	/* if the chunk is not empty - ignoring reserve */
-	if (last_alloc >= s_index) {
-		as_len = last_alloc + 1 - s_index;
-
-		/*
-		 * Iterate through chunk map computing size info.
-		 * The first bit is overloaded to be a used flag.
-		 * negative = free space, positive = allocated
-		 */
-		for (i = 0, p = chunk->map + s_index; i < as_len; i++, p++) {
-			alloc_sign = (*p & 1) ? 1 : -1;
-			alloc_sizes[i] = alloc_sign *
-				((p[1] & ~1) - (p[0] & ~1));
+	/*
+	 * find_last_bit returns the start value if nothing found.
+	 * Therefore, we must determine if it is a failure of find_last_bit
+	 * and set the appropriate value.
+	 */
+	last_alloc = find_last_bit(chunk->alloc_map,
+				   pcpu_chunk_map_bits(chunk) -
+				   chunk->end_offset / PCPU_MIN_ALLOC_SIZE - 1);
+	last_alloc = test_bit(last_alloc, chunk->alloc_map) ?
+		     last_alloc + 1 : 0;
+
+	as_len = 0;
+	start = chunk->start_offset;
+
+	/*
+	 * If a bit is set in the allocation map, the bound_map identifies
+	 * where the allocation ends.  If the allocation is not set, the
+	 * bound_map does not identify free areas as it is only kept accurate
+	 * on allocation, not free.
+	 *
+	 * Positive values are allocations and negative values are free
+	 * fragments.
+	 */
+	while (start < last_alloc) {
+		if (test_bit(start, chunk->alloc_map)) {
+			end = find_next_bit(chunk->bound_map, last_alloc,
+					    start + 1);
+			alloc_sizes[as_len] = 1;
+		} else {
+			end = find_next_bit(chunk->alloc_map, last_alloc,
+					    start + 1);
+			alloc_sizes[as_len] = -1;
 		}
 
-		sort(alloc_sizes, as_len, sizeof(chunk->map[0]), cmpint, NULL);
+		alloc_sizes[as_len++] *= (end - start) * PCPU_MIN_ALLOC_SIZE;
+
+		start = end;
+	}
+
+	/*
+	 * The negative values are free fragments and thus sorting gives the
+	 * free fragments at the beginning in largest first order.
+	 */
+	if (as_len > 0) {
+		sort(alloc_sizes, as_len, sizeof(int), cmpint, NULL);
 
-		/* Iterate through the unallocated fragements. */
+		/* iterate through the unallocated fragments */
 		for (i = 0, p = alloc_sizes; *p < 0 && i < as_len; i++, p++) {
 			sum_frag -= *p;
 			max_frag = max(max_frag, -1 * (*p));
@@ -99,8 +120,10 @@ static void chunk_map_stats(struct seq_file *m, struct pcpu_chunk *chunk,
 
 	P("nr_alloc", chunk->nr_alloc);
 	P("max_alloc_size", chunk->max_alloc_size);
-	P("free_size", chunk->free_size);
-	P("contig_hint", chunk->contig_hint);
+	P("empty_pop_pages", chunk->nr_empty_pop_pages);
+	P("first_bit", chunk->first_bit);
+	P("free_bytes", chunk->free_bytes);
+	P("contig_bytes", chunk->contig_bits * PCPU_MIN_ALLOC_SIZE);
 	P("sum_frag", sum_frag);
 	P("max_frag", max_frag);
 	P("cur_min_alloc", cur_min_alloc);
@@ -112,29 +135,30 @@ static void chunk_map_stats(struct seq_file *m, struct pcpu_chunk *chunk,
 static int percpu_stats_show(struct seq_file *m, void *v)
 {
 	struct pcpu_chunk *chunk;
-	int slot, max_map_used;
-	void *buffer;
+	int slot, max_nr_alloc;
+	int *buffer;
 
 alloc_buffer:
 	spin_lock_irq(&pcpu_lock);
-	max_map_used = find_max_map_used();
+	max_nr_alloc = find_max_nr_alloc();
 	spin_unlock_irq(&pcpu_lock);
 
-	buffer = vmalloc(max_map_used * sizeof(pcpu_first_chunk->map[0]));
+	/* there can be at most this many free and allocated fragments */
+	buffer = vmalloc((2 * max_nr_alloc + 1) * sizeof(int));
 	if (!buffer)
 		return -ENOMEM;
 
 	spin_lock_irq(&pcpu_lock);
 
 	/* if the buffer allocated earlier is too small */
-	if (max_map_used < find_max_map_used()) {
+	if (max_nr_alloc < find_max_nr_alloc()) {
 		spin_unlock_irq(&pcpu_lock);
 		vfree(buffer);
 		goto alloc_buffer;
 	}
 
 #define PL(X) \
-	seq_printf(m, "  %-24s: %8lld\n", #X, (long long int)pcpu_stats_ai.X)
+	seq_printf(m, "  %-20s: %12lld\n", #X, (long long int)pcpu_stats_ai.X)
 
 	seq_printf(m,
 			"Percpu Memory Statistics\n"
@@ -151,7 +175,7 @@ alloc_buffer:
 #undef PL
 
 #define PU(X) \
-	seq_printf(m, "  %-18s: %14llu\n", #X, (unsigned long long)pcpu_stats.X)
+	seq_printf(m, "  %-20s: %12llu\n", #X, (unsigned long long)pcpu_stats.X)
 
 	seq_printf(m,
 			"Global Stats:\n"
@@ -164,6 +188,7 @@ alloc_buffer:
 	PU(nr_max_chunks);
 	PU(min_alloc_size);
 	PU(max_alloc_size);
+	P("empty_pop_pages", pcpu_nr_empty_pop_pages);
 	seq_putc(m, '\n');
 
 #undef PU

mm/percpu.c

@@ -4,44 +4,53 @@
  * Copyright (C) 2009		SUSE Linux Products GmbH
  * Copyright (C) 2009		Tejun Heo <tj@kernel.org>
  *
- * This file is released under the GPLv2.
+ * Copyright (C) 2017		Facebook Inc.
+ * Copyright (C) 2017		Dennis Zhou <dennisszhou@gmail.com>
  *
- * 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.
+ * This file is released under the GPLv2 license.
+ *
+ * The percpu allocator handles both static and dynamic areas.  Percpu
+ * areas are allocated in chunks which are divided into units.  There is
+ * a 1-to-1 mapping for units to possible cpus.  These units are grouped
+ * based on NUMA properties of the machine.
  *
  *  c0                           c1                         c2
  *  -------------------          -------------------        ------------
  * | u0 | u1 | u2 | u3 |        | u0 | u1 | u2 | u3 |      | u0 | u1 | u
  *  -------------------  ......  -------------------  ....  ------------
  *
- * Allocation is done 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 equal 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.
+ * 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:
  *
@@ -58,6 +67,7 @@
 #include <linux/bitmap.h>
 #include <linux/bootmem.h>
 #include <linux/err.h>
+#include <linux/lcm.h>
 #include <linux/list.h>
 #include <linux/log2.h>
 #include <linux/mm.h>
@@ -81,10 +91,9 @@
 
 #include "percpu-internal.h"
 
-#define PCPU_SLOT_BASE_SHIFT		5	/* 1-31 shares the same slot */
-#define PCPU_DFL_MAP_ALLOC		16	/* start a map with 16 ents */
-#define PCPU_ATOMIC_MAP_MARGIN_LOW	32
-#define PCPU_ATOMIC_MAP_MARGIN_HIGH	64
+/* the slots are sorted by free bytes left, 1-31 bytes share the same slot */
+#define PCPU_SLOT_BASE_SHIFT		5
+
 #define PCPU_EMPTY_POP_PAGES_LOW	2
 #define PCPU_EMPTY_POP_PAGES_HIGH	4
 
@@ -140,13 +149,10 @@ 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.  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.
+ * 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;
-static int pcpu_reserved_chunk_limit __ro_after_init;
 
 DEFINE_SPINLOCK(pcpu_lock);	/* all internal data structures */
 static DEFINE_MUTEX(pcpu_alloc_mutex);	/* chunk create/destroy, [de]pop, map ext */
@@ -160,7 +166,7 @@ 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.
  */
-static int pcpu_nr_empty_pop_pages;
+int pcpu_nr_empty_pop_pages;
 
 /*
  * Balance work is used to populate or destroy chunks asynchronously.  We
@@ -179,19 +185,26 @@ static void pcpu_schedule_balance_work(void)
 		schedule_work(&pcpu_balance_work);
 }
 
-static bool pcpu_addr_in_first_chunk(void *addr)
+/**
+ * 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 *first_start = pcpu_first_chunk->base_addr;
+	void *start_addr, *end_addr;
 
-	return addr >= first_start && addr < first_start + pcpu_unit_size;
-}
+	if (!chunk)
+		return false;
 
-static bool pcpu_addr_in_reserved_chunk(void *addr)
-{
-	void *first_start = pcpu_first_chunk->base_addr;
+	start_addr = chunk->base_addr + chunk->start_offset;
+	end_addr = chunk->base_addr + chunk->nr_pages * PAGE_SIZE -
+		   chunk->end_offset;
 
-	return addr >= first_start &&
-		addr < first_start + pcpu_reserved_chunk_limit;
+	return addr >= start_addr && addr < end_addr;
 }
 
 static int __pcpu_size_to_slot(int size)
@@ -209,10 +222,10 @@ static int pcpu_size_to_slot(int size)
 
 static int pcpu_chunk_slot(const struct pcpu_chunk *chunk)
 {
-	if (chunk->free_size < sizeof(int) || chunk->contig_hint < sizeof(int))
+	if (chunk->free_bytes < PCPU_MIN_ALLOC_SIZE || chunk->contig_bits == 0)
 		return 0;
 
-	return pcpu_size_to_slot(chunk->free_size);
+	return pcpu_size_to_slot(chunk->free_bytes);
 }
 
 /* set the pointer to a chunk in a page struct */
@@ -232,42 +245,200 @@ 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_offsets[cpu] +
-		(page_idx << PAGE_SHIFT);
+	return (unsigned long)chunk->base_addr +
+	       pcpu_unit_page_offset(cpu, page_idx);
 }
 
-static void __maybe_unused pcpu_next_unpop(struct pcpu_chunk *chunk,
-					   int *rs, int *re, int end)
+static void pcpu_next_unpop(unsigned long *bitmap, int *rs, int *re, int end)
 {
-	*rs = find_next_zero_bit(chunk->populated, end, *rs);
-	*re = find_next_bit(chunk->populated, end, *rs + 1);
+	*rs = find_next_zero_bit(bitmap, end, *rs);
+	*re = find_next_bit(bitmap, end, *rs + 1);
 }
 
-static void __maybe_unused pcpu_next_pop(struct pcpu_chunk *chunk,
-					 int *rs, int *re, int end)
+static void pcpu_next_pop(unsigned long *bitmap, int *rs, int *re, int end)
 {
-	*rs = find_next_bit(chunk->populated, end, *rs);
-	*re = find_next_zero_bit(chunk->populated, end, *rs + 1);
+	*rs = find_next_bit(bitmap, end, *rs);
+	*re = find_next_zero_bit(bitmap, end, *rs + 1);
 }
 
 /*
- * (Un)populated page region iterators.  Iterate over (un)populated
- * page regions between @start and @end in @chunk.  @rs and @re should
- * be integer variables and will be set to start and end page index of
- * the current region.
+ * 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_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;
+		}
+
+		*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.
  */
-#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)))
+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) {
+			*bits += alloc_bits + block->contig_hint_start -
+				 block->first_free;
+			*bit_off = pcpu_block_off_to_off(i, block->first_free);
+			return;
+		}
+
+		*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;
+	}
 
-#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)))
+	/* 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
@@ -305,38 +476,6 @@ static void pcpu_mem_free(void *ptr)
 	kvfree(ptr);
 }
 
-/**
- * pcpu_count_occupied_pages - count the number of pages an area occupies
- * @chunk: chunk of interest
- * @i: index of the area in question
- *
- * Count the number of pages chunk's @i'th area occupies.  When the area's
- * start and/or end address isn't aligned to page boundary, the straddled
- * page is included in the count iff the rest of the page is free.
- */
-static int pcpu_count_occupied_pages(struct pcpu_chunk *chunk, int i)
-{
-	int off = chunk->map[i] & ~1;
-	int end = chunk->map[i + 1] & ~1;
-
-	if (!PAGE_ALIGNED(off) && i > 0) {
-		int prev = chunk->map[i - 1];
-
-		if (!(prev & 1) && prev <= round_down(off, PAGE_SIZE))
-			off = round_down(off, PAGE_SIZE);
-	}
-
-	if (!PAGE_ALIGNED(end) && i + 1 < chunk->map_used) {
-		int next = chunk->map[i + 1];
-		int nend = chunk->map[i + 2] & ~1;
-
-		if (!(next & 1) && nend >= round_up(end, PAGE_SIZE))
-			end = round_up(end, PAGE_SIZE);
-	}
-
-	return max_t(int, PFN_DOWN(end) - PFN_UP(off), 0);
-}
-
 /**
  * pcpu_chunk_relocate - put chunk in the appropriate chunk slot
  * @chunk: chunk of interest
@@ -363,383 +502,706 @@ static void pcpu_chunk_relocate(struct pcpu_chunk *chunk, int oslot)
 }
 
 /**
- * pcpu_need_to_extend - determine whether chunk area map needs to be extended
+ * pcpu_cnt_pop_pages- counts populated backing pages in range
  * @chunk: chunk of interest
- * @is_atomic: the allocation context
+ * @bit_off: start offset
+ * @bits: size of area to check
  *
- * Determine whether area map of @chunk needs to be extended.  If
- * @is_atomic, only the amount necessary for a new allocation is
- * considered; however, async extension is scheduled if the left amount is
- * low.  If !@is_atomic, it aims for more empty space.  Combined, this
- * ensures that the map is likely to have enough available space to
- * accomodate atomic allocations which can't extend maps directly.
- *
- * CONTEXT:
- * pcpu_lock.
+ * Calculates the number of populated pages in the region
+ * [page_start, page_end).  This keeps track of how many empty populated
+ * pages are available and decide if async work should be scheduled.
  *
  * RETURNS:
- * New target map allocation length if extension is necessary, 0
- * otherwise.
+ * The nr of populated pages.
  */
-static int pcpu_need_to_extend(struct pcpu_chunk *chunk, bool is_atomic)
+static inline int pcpu_cnt_pop_pages(struct pcpu_chunk *chunk, int bit_off,
+				     int bits)
 {
-	int margin, new_alloc;
-
-	lockdep_assert_held(&pcpu_lock);
-
-	if (is_atomic) {
-		margin = 3;
+	int page_start = PFN_UP(bit_off * PCPU_MIN_ALLOC_SIZE);
+	int page_end = PFN_DOWN((bit_off + bits) * PCPU_MIN_ALLOC_SIZE);
 
-		if (chunk->map_alloc <
-		    chunk->map_used + PCPU_ATOMIC_MAP_MARGIN_LOW) {
-			if (list_empty(&chunk->map_extend_list)) {
-				list_add_tail(&chunk->map_extend_list,
-					      &pcpu_map_extend_chunks);
-				pcpu_schedule_balance_work();
-			}
-		}
-	} else {
-		margin = PCPU_ATOMIC_MAP_MARGIN_HIGH;
-	}
-
-	if (chunk->map_alloc >= chunk->map_used + margin)
+	if (page_start >= page_end)
 		return 0;
 
-	new_alloc = PCPU_DFL_MAP_ALLOC;
-	while (new_alloc < chunk->map_used + margin)
-		new_alloc *= 2;
-
-	return new_alloc;
+	/*
+	 * bitmap_weight counts the number of bits set in a bitmap up to
+	 * the specified number of bits.  This is counting the populated
+	 * pages up to page_end and then subtracting the populated pages
+	 * up to page_start to count the populated pages in
+	 * [page_start, page_end).
+	 */
+	return bitmap_weight(chunk->populated, page_end) -
+	       bitmap_weight(chunk->populated, page_start);
 }
 
 /**
- * pcpu_extend_area_map - extend area map of a chunk
+ * pcpu_chunk_update - updates the chunk metadata given a free area
  * @chunk: chunk of interest
- * @new_alloc: new target allocation length of the area map
+ * @bit_off: chunk offset
+ * @bits: size of free area
  *
- * Extend area map of @chunk to have @new_alloc entries.
+ * This updates the chunk's contig hint and starting offset given a free area.
+ * Choose the best starting offset if the contig hint is equal.
+ */
+static void pcpu_chunk_update(struct pcpu_chunk *chunk, int bit_off, int bits)
+{
+	if (bits > chunk->contig_bits) {
+		chunk->contig_bits_start = bit_off;
+		chunk->contig_bits = bits;
+	} else if (bits == chunk->contig_bits && chunk->contig_bits_start &&
+		   (!bit_off ||
+		    __ffs(bit_off) > __ffs(chunk->contig_bits_start))) {
+		/* use the start with the best alignment */
+		chunk->contig_bits_start = bit_off;
+	}
+}
+
+/**
+ * pcpu_chunk_refresh_hint - updates metadata about a chunk
+ * @chunk: chunk of interest
  *
- * CONTEXT:
- * Does GFP_KERNEL allocation.  Grabs and releases pcpu_lock.
+ * Iterates over the metadata blocks to find the largest contig area.
+ * It also counts the populated pages and uses the delta to update the
+ * global count.
  *
- * RETURNS:
- * 0 on success, -errno on failure.
+ * Updates:
+ *      chunk->contig_bits
+ *      chunk->contig_bits_start
+ *      nr_empty_pop_pages (chunk and global)
  */
-static int pcpu_extend_area_map(struct pcpu_chunk *chunk, int new_alloc)
+static void pcpu_chunk_refresh_hint(struct pcpu_chunk *chunk)
 {
-	int *old = NULL, *new = NULL;
-	size_t old_size = 0, new_size = new_alloc * sizeof(new[0]);
-	unsigned long flags;
+	int bit_off, bits, nr_empty_pop_pages;
 
-	lockdep_assert_held(&pcpu_alloc_mutex);
+	/* clear metadata */
+	chunk->contig_bits = 0;
 
-	new = pcpu_mem_zalloc(new_size);
-	if (!new)
-		return -ENOMEM;
+	bit_off = chunk->first_bit;
+	bits = nr_empty_pop_pages = 0;
+	pcpu_for_each_md_free_region(chunk, bit_off, bits) {
+		pcpu_chunk_update(chunk, bit_off, bits);
 
-	/* acquire pcpu_lock and switch to new area map */
-	spin_lock_irqsave(&pcpu_lock, flags);
+		nr_empty_pop_pages += pcpu_cnt_pop_pages(chunk, bit_off, bits);
+	}
 
-	if (new_alloc <= chunk->map_alloc)
-		goto out_unlock;
+	/*
+	 * Keep track of nr_empty_pop_pages.
+	 *
+	 * The chunk maintains the previous number of free pages it held,
+	 * so the delta is used to update the global counter.  The reserved
+	 * chunk is not part of the free page count as they are populated
+	 * at init and are special to serving reserved allocations.
+	 */
+	if (chunk != pcpu_reserved_chunk)
+		pcpu_nr_empty_pop_pages +=
+			(nr_empty_pop_pages - chunk->nr_empty_pop_pages);
 
-	old_size = chunk->map_alloc * sizeof(chunk->map[0]);
-	old = chunk->map;
+	chunk->nr_empty_pop_pages = nr_empty_pop_pages;
+}
 
-	memcpy(new, old, old_size);
+/**
+ * pcpu_block_update - updates a block given a free area
+ * @block: block of interest
+ * @start: start offset in block
+ * @end: end offset in block
+ *
+ * Updates a block given a known free area.  The region [start, end) is
+ * expected to be the entirety of the free area within a block.  Chooses
+ * the best starting offset if the contig hints are equal.
+ */
+static void pcpu_block_update(struct pcpu_block_md *block, int start, int end)
+{
+	int contig = end - start;
+
+	block->first_free = min(block->first_free, start);
+	if (start == 0)
+		block->left_free = contig;
+
+	if (end == PCPU_BITMAP_BLOCK_BITS)
+		block->right_free = contig;
+
+	if (contig > block->contig_hint) {
+		block->contig_hint_start = start;
+		block->contig_hint = contig;
+	} else if (block->contig_hint_start && contig == block->contig_hint &&
+		   (!start || __ffs(start) > __ffs(block->contig_hint_start))) {
+		/* use the start with the best alignment */
+		block->contig_hint_start = start;
+	}
+}
 
-	chunk->map_alloc = new_alloc;
-	chunk->map = new;
-	new = NULL;
+/**
+ * pcpu_block_refresh_hint
+ * @chunk: chunk of interest
+ * @index: index of the metadata block
+ *
+ * Scans over the block beginning at first_free and updates the block
+ * metadata accordingly.
+ */
+static void pcpu_block_refresh_hint(struct pcpu_chunk *chunk, int index)
+{
+	struct pcpu_block_md *block = chunk->md_blocks + index;
+	unsigned long *alloc_map = pcpu_index_alloc_map(chunk, index);
+	int rs, re;	/* region start, region end */
+
+	/* clear hints */
+	block->contig_hint = 0;
+	block->left_free = block->right_free = 0;
+
+	/* iterate over free areas and update the contig hints */
+	pcpu_for_each_unpop_region(alloc_map, rs, re, block->first_free,
+				   PCPU_BITMAP_BLOCK_BITS) {
+		pcpu_block_update(block, rs, re);
+	}
+}
 
-out_unlock:
-	spin_unlock_irqrestore(&pcpu_lock, flags);
+/**
+ * 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 *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 */
 
 	/*
-	 * pcpu_mem_free() might end up calling vfree() which uses
-	 * IRQ-unsafe lock and thus can't be called under pcpu_lock.
+	 * 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.
 	 */
-	pcpu_mem_free(old);
-	pcpu_mem_free(new);
+	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;
 
-	return 0;
+	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_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 (s_off >= s_block->contig_hint_start &&
+	    s_off < s_block->contig_hint_start + s_block->contig_hint) {
+		/* block contig hint is broken - scan to fix it */
+		pcpu_block_refresh_hint(chunk, s_index);
+	} else {
+		/* update left and right contig manually */
+		s_block->left_free = min(s_block->left_free, s_off);
+		if (s_index == e_index)
+			s_block->right_free = min_t(int, s_block->right_free,
+					PCPU_BITMAP_BLOCK_BITS - e_off);
+		else
+			s_block->right_free = 0;
+	}
+
+	/*
+	 * Update e_block.
+	 */
+	if (s_index != e_index) {
+		/*
+		 * 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->contig_hint_start) {
+				/* contig hint is broken - scan to fix it */
+				pcpu_block_refresh_hint(chunk, e_index);
+			} else {
+				e_block->left_free = 0;
+				e_block->right_free =
+					min_t(int, e_block->right_free,
+					      PCPU_BITMAP_BLOCK_BITS - e_off);
+			}
+		}
+
+		/* update in-between md_blocks */
+		for (block = s_block + 1; block < e_block; block++) {
+			block->contig_hint = 0;
+			block->left_free = 0;
+			block->right_free = 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 (bit_off >= chunk->contig_bits_start  &&
+	    bit_off < chunk->contig_bits_start + chunk->contig_bits)
+		pcpu_chunk_refresh_hint(chunk);
 }
 
 /**
- * pcpu_fit_in_area - try to fit the requested allocation in a candidate area
- * @chunk: chunk the candidate area belongs to
- * @off: the offset to the start of the candidate area
- * @this_size: the size of the candidate area
- * @size: the size of the target allocation
- * @align: the alignment of the target allocation
- * @pop_only: only allocate from already populated region
- *
- * We're trying to allocate @size bytes aligned at @align.  @chunk's area
- * at @off sized @this_size is a candidate.  This function determines
- * whether the target allocation fits in the candidate area and returns the
- * number of bytes to pad after @off.  If the target area doesn't fit, -1
- * is returned.
- *
- * If @pop_only is %true, this function only considers the already
- * populated part of the candidate area.
+ * pcpu_block_update_hint_free - updates the block hints on the free path
+ * @chunk: chunk of interest
+ * @bit_off: chunk offset
+ * @bits: size of request
+ *
+ * Updates metadata for the allocation path.  This avoids a blind block
+ * refresh by making use of the block contig hints.  If this fails, it scans
+ * forward and backward to determine the extent of the free area.  This is
+ * capped at the boundary of blocks.
+ *
+ * A chunk update is triggered if a page becomes free, a block becomes free,
+ * or the free spans across blocks.  This tradeoff is to minimize iterating
+ * over the block metadata to update chunk->contig_bits.  chunk->contig_bits
+ * may be off by up to a page, but it will never be more than the available
+ * space.  If the contig hint is contained in one block, it will be accurate.
  */
-static int pcpu_fit_in_area(struct pcpu_chunk *chunk, int off, int this_size,
-			    int size, int align, bool pop_only)
+static void pcpu_block_update_hint_free(struct pcpu_chunk *chunk, int bit_off,
+					int bits)
 {
-	int cand_off = off;
-
-	while (true) {
-		int head = ALIGN(cand_off, align) - off;
-		int page_start, page_end, rs, re;
+	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 */
 
-		if (this_size < head + size)
-			return -1;
+	/*
+	 * 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;
 
-		if (!pop_only)
-			return head;
+	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 {
 		/*
-		 * If the first unpopulated page is beyond the end of the
-		 * allocation, the whole allocation is populated;
-		 * otherwise, retry from the end of the unpopulated area.
+		 * 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.
 		 */
-		page_start = PFN_DOWN(head + off);
-		page_end = PFN_UP(head + off + size);
-
-		rs = page_start;
-		pcpu_next_unpop(chunk, &rs, &re, PFN_UP(off + this_size));
-		if (rs >= page_end)
-			return head;
-		cand_off = re * PAGE_SIZE;
+		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;
+	pcpu_block_update(s_block, start, e_off);
+
+	/* freeing in the same block */
+	if (s_index != e_index) {
+		/* update e_block */
+		pcpu_block_update(e_block, 0, end);
+
+		/* reset md_blocks in the middle */
+		for (block = s_block + 1; block < e_block; block++) {
+			block->first_free = 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;
+		}
 	}
+
+	/*
+	 * Refresh chunk metadata when the free makes a page free, a block
+	 * free, or spans across blocks.  The contig hint may be off by up to
+	 * a page, but if the hint is contained in a block, it will be accurate
+	 * with the else condition below.
+	 */
+	if ((ALIGN_DOWN(end, min(PCPU_BITS_PER_PAGE, PCPU_BITMAP_BLOCK_BITS)) >
+	     ALIGN(start, min(PCPU_BITS_PER_PAGE, PCPU_BITMAP_BLOCK_BITS))) ||
+	    s_index != e_index)
+		pcpu_chunk_refresh_hint(chunk);
+	else
+		pcpu_chunk_update(chunk, pcpu_block_off_to_off(s_index, start),
+				  s_block->contig_hint);
 }
 
 /**
- * pcpu_alloc_area - allocate area from a pcpu_chunk
+ * pcpu_is_populated - determines if the region is populated
  * @chunk: chunk of interest
- * @size: wanted size in bytes
- * @align: wanted align
- * @pop_only: allocate only from the populated area
- * @occ_pages_p: out param for the number of pages the area occupies
- *
- * Try to allocate @size bytes area aligned at @align from @chunk.
- * Note that this function only allocates the offset.  It doesn't
- * populate or map the area.
+ * @bit_off: chunk offset
+ * @bits: size of area
+ * @next_off: return value for the next offset to start searching
  *
- * @chunk->map must have at least two free slots.
+ * For atomic allocations, check if the backing pages are populated.
  *
- * CONTEXT:
- * pcpu_lock.
+ * 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:
- * Allocated offset in @chunk on success, -1 if no matching area is
- * found.
+ * The offset in the bitmap to begin searching.
+ * -1 if no offset is found.
  */
-static int pcpu_alloc_area(struct pcpu_chunk *chunk, int size, int align,
-			   bool pop_only, int *occ_pages_p)
+static int pcpu_find_block_fit(struct pcpu_chunk *chunk, int alloc_bits,
+			       size_t align, bool pop_only)
 {
-	int oslot = pcpu_chunk_slot(chunk);
-	int max_contig = 0;
-	int i, off;
-	bool seen_free = false;
-	int *p;
-
-	for (i = chunk->first_free, p = chunk->map + i; i < chunk->map_used; i++, p++) {
-		int head, tail;
-		int this_size;
-
-		off = *p;
-		if (off & 1)
-			continue;
+	int bit_off, bits, next_off;
 
-		this_size = (p[1] & ~1) - off;
+	/*
+	 * Check to see if the allocation can fit in the chunk's contig hint.
+	 * This is an optimization to prevent scanning by assuming if it
+	 * cannot fit in the global hint, there is memory pressure and creating
+	 * a new chunk would happen soon.
+	 */
+	bit_off = ALIGN(chunk->contig_bits_start, align) -
+		  chunk->contig_bits_start;
+	if (bit_off + alloc_bits > chunk->contig_bits)
+		return -1;
+
+	bit_off = chunk->first_bit;
+	bits = 0;
+	pcpu_for_each_fit_region(chunk, alloc_bits, align, bit_off, bits) {
+		if (!pop_only || pcpu_is_populated(chunk, bit_off, bits,
+						   &next_off))
+			break;
 
-		head = pcpu_fit_in_area(chunk, off, this_size, size, align,
-					pop_only);
-		if (head < 0) {
-			if (!seen_free) {
-				chunk->first_free = i;
-				seen_free = true;
-			}
-			max_contig = max(this_size, max_contig);
-			continue;
-		}
+		bit_off = next_off;
+		bits = 0;
+	}
 
-		/*
-		 * If head is small or the previous block is free,
-		 * merge'em.  Note that 'small' is defined as smaller
-		 * than sizeof(int), which is very small but isn't too
-		 * uncommon for percpu allocations.
-		 */
-		if (head && (head < sizeof(int) || !(p[-1] & 1))) {
-			*p = off += head;
-			if (p[-1] & 1)
-				chunk->free_size -= head;
-			else
-				max_contig = max(*p - p[-1], max_contig);
-			this_size -= head;
-			head = 0;
-		}
+	if (bit_off == pcpu_chunk_map_bits(chunk))
+		return -1;
 
-		/* if tail is small, just keep it around */
-		tail = this_size - head - size;
-		if (tail < sizeof(int)) {
-			tail = 0;
-			size = this_size - head;
-		}
+	return bit_off;
+}
 
-		/* split if warranted */
-		if (head || tail) {
-			int nr_extra = !!head + !!tail;
-
-			/* insert new subblocks */
-			memmove(p + nr_extra + 1, p + 1,
-				sizeof(chunk->map[0]) * (chunk->map_used - i));
-			chunk->map_used += nr_extra;
-
-			if (head) {
-				if (!seen_free) {
-					chunk->first_free = i;
-					seen_free = true;
-				}
-				*++p = off += head;
-				++i;
-				max_contig = max(head, max_contig);
-			}
-			if (tail) {
-				p[1] = off + size;
-				max_contig = max(tail, max_contig);
-			}
-		}
+/**
+ * pcpu_alloc_area - allocates an area from a pcpu_chunk
+ * @chunk: chunk of interest
+ * @alloc_bits: size of request in allocation units
+ * @align: alignment of area (max PAGE_SIZE)
+ * @start: bit_off to start searching
+ *
+ * This function takes in a @start offset to begin searching to fit an
+ * allocation of @alloc_bits with alignment @align.  It needs to scan
+ * the allocation map because if it fits within the block's contig hint,
+ * @start will be block->first_free. This is an attempt to fill the
+ * allocation prior to breaking the contig hint.  The allocation and
+ * boundary maps are updated accordingly if it confirms a valid
+ * free area.
+ *
+ * RETURNS:
+ * Allocated addr offset in @chunk on success.
+ * -1 if no matching area is found.
+ */
+static int pcpu_alloc_area(struct pcpu_chunk *chunk, int alloc_bits,
+			   size_t align, int start)
+{
+	size_t align_mask = (align) ? (align - 1) : 0;
+	int bit_off, end, oslot;
 
-		if (!seen_free)
-			chunk->first_free = i + 1;
+	lockdep_assert_held(&pcpu_lock);
 
-		/* update hint and mark allocated */
-		if (i + 1 == chunk->map_used)
-			chunk->contig_hint = max_contig; /* fully scanned */
-		else
-			chunk->contig_hint = max(chunk->contig_hint,
-						 max_contig);
+	oslot = pcpu_chunk_slot(chunk);
 
-		chunk->free_size -= size;
-		*p |= 1;
+	/*
+	 * Search to find a fit.
+	 */
+	end = start + alloc_bits + PCPU_BITMAP_BLOCK_BITS;
+	bit_off = bitmap_find_next_zero_area(chunk->alloc_map, end, start,
+					     alloc_bits, align_mask);
+	if (bit_off >= end)
+		return -1;
 
-		*occ_pages_p = pcpu_count_occupied_pages(chunk, i);
-		pcpu_chunk_relocate(chunk, oslot);
-		return off;
-	}
+	/* update alloc map */
+	bitmap_set(chunk->alloc_map, bit_off, alloc_bits);
+
+	/* update boundary map */
+	set_bit(bit_off, chunk->bound_map);
+	bitmap_clear(chunk->bound_map, bit_off + 1, alloc_bits - 1);
+	set_bit(bit_off + alloc_bits, chunk->bound_map);
+
+	chunk->free_bytes -= alloc_bits * PCPU_MIN_ALLOC_SIZE;
+
+	/* update first free bit */
+	if (bit_off == chunk->first_bit)
+		chunk->first_bit = find_next_zero_bit(
+					chunk->alloc_map,
+					pcpu_chunk_map_bits(chunk),
+					bit_off + alloc_bits);
+
+	pcpu_block_update_hint_alloc(chunk, bit_off, alloc_bits);
 
-	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;
+	return bit_off * PCPU_MIN_ALLOC_SIZE;
 }
 
 /**
- * pcpu_free_area - free area to a pcpu_chunk
+ * pcpu_free_area - frees the corresponding offset
  * @chunk: chunk of interest
- * @freeme: offset of area to free
- * @occ_pages_p: out param for the number of pages the area occupies
- *
- * Free area starting from @freeme to @chunk.  Note that this function
- * only modifies the allocation map.  It doesn't depopulate or unmap
- * the area.
+ * @off: addr offset into chunk
  *
- * CONTEXT:
- * pcpu_lock.
+ * 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 freeme,
-			   int *occ_pages_p)
+static void pcpu_free_area(struct pcpu_chunk *chunk, int off)
 {
-	int oslot = pcpu_chunk_slot(chunk);
-	int off = 0;
-	unsigned i, j;
-	int to_free = 0;
-	int *p;
+	int bit_off, bits, end, oslot;
 
 	lockdep_assert_held(&pcpu_lock);
 	pcpu_stats_area_dealloc(chunk);
 
-	freeme |= 1;	/* we are searching for <given offset, in use> pair */
-
-	i = 0;
-	j = chunk->map_used;
-	while (i != j) {
-		unsigned k = (i + j) / 2;
-		off = chunk->map[k];
-		if (off < freeme)
-			i = k + 1;
-		else if (off > freeme)
-			j = k;
-		else
-			i = j = k;
+	oslot = pcpu_chunk_slot(chunk);
+
+	bit_off = off / PCPU_MIN_ALLOC_SIZE;
+
+	/* find end index */
+	end = find_next_bit(chunk->bound_map, pcpu_chunk_map_bits(chunk),
+			    bit_off + 1);
+	bits = end - bit_off;
+	bitmap_clear(chunk->alloc_map, bit_off, bits);
+
+	/* update metadata */
+	chunk->free_bytes += bits * PCPU_MIN_ALLOC_SIZE;
+
+	/* update first free bit */
+	chunk->first_bit = min(chunk->first_bit, bit_off);
+
+	pcpu_block_update_hint_free(chunk, bit_off, bits);
+
+	pcpu_chunk_relocate(chunk, oslot);
+}
+
+static void pcpu_init_md_blocks(struct pcpu_chunk *chunk)
+{
+	struct pcpu_block_md *md_block;
+
+	for (md_block = chunk->md_blocks;
+	     md_block != chunk->md_blocks + pcpu_chunk_nr_blocks(chunk);
+	     md_block++) {
+		md_block->contig_hint = PCPU_BITMAP_BLOCK_BITS;
+		md_block->left_free = PCPU_BITMAP_BLOCK_BITS;
+		md_block->right_free = PCPU_BITMAP_BLOCK_BITS;
 	}
-	BUG_ON(off != freeme);
+}
 
-	if (i < chunk->first_free)
-		chunk->first_free = i;
+/**
+ * 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;
 
-	p = chunk->map + i;
-	*p = off &= ~1;
-	chunk->free_size += (p[1] & ~1) - off;
+	/* region calculations */
+	aligned_addr = tmp_addr & PAGE_MASK;
 
-	*occ_pages_p = pcpu_count_occupied_pages(chunk, i);
+	start_offset = tmp_addr - aligned_addr;
 
-	/* merge with next? */
-	if (!(p[1] & 1))
-		to_free++;
-	/* merge with previous? */
-	if (i > 0 && !(p[-1] & 1)) {
-		to_free++;
-		i--;
-		p--;
+	/*
+	 * 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 */
+	chunk = memblock_virt_alloc(sizeof(struct pcpu_chunk) +
+				    BITS_TO_LONGS(region_size >> PAGE_SHIFT),
+				    0);
+
+	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);
+
+	chunk->alloc_map = memblock_virt_alloc(BITS_TO_LONGS(region_bits) *
+					       sizeof(chunk->alloc_map[0]), 0);
+	chunk->bound_map = memblock_virt_alloc(BITS_TO_LONGS(region_bits + 1) *
+					       sizeof(chunk->bound_map[0]), 0);
+	chunk->md_blocks = memblock_virt_alloc(pcpu_chunk_nr_blocks(chunk) *
+					       sizeof(chunk->md_blocks[0]), 0);
+	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 =
+		pcpu_cnt_pop_pages(chunk, start_offset / PCPU_MIN_ALLOC_SIZE,
+				   map_size / PCPU_MIN_ALLOC_SIZE);
+
+	chunk->contig_bits = map_size / PCPU_MIN_ALLOC_SIZE;
+	chunk->free_bytes = map_size;
+
+	if (chunk->start_offset) {
+		/* hide the beginning of the bitmap */
+		offset_bits = chunk->start_offset / PCPU_MIN_ALLOC_SIZE;
+		bitmap_set(chunk->alloc_map, 0, offset_bits);
+		set_bit(0, chunk->bound_map);
+		set_bit(offset_bits, chunk->bound_map);
+
+		chunk->first_bit = offset_bits;
+
+		pcpu_block_update_hint_alloc(chunk, 0, offset_bits);
 	}
-	if (to_free) {
-		chunk->map_used -= to_free;
-		memmove(p + 1, p + 1 + to_free,
-			(chunk->map_used - i) * sizeof(chunk->map[0]));
+
+	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);
 	}
 
-	chunk->contig_hint = max(chunk->map[i + 1] - chunk->map[i] - 1, chunk->contig_hint);
-	pcpu_chunk_relocate(chunk, oslot);
+	return chunk;
 }
 
 static struct pcpu_chunk *pcpu_alloc_chunk(void)
 {
 	struct pcpu_chunk *chunk;
+	int region_bits;
 
 	chunk = pcpu_mem_zalloc(pcpu_chunk_struct_size);
 	if (!chunk)
 		return NULL;
 
-	chunk->map = pcpu_mem_zalloc(PCPU_DFL_MAP_ALLOC *
-						sizeof(chunk->map[0]));
-	if (!chunk->map) {
-		pcpu_mem_free(chunk);
-		return NULL;
-	}
+	INIT_LIST_HEAD(&chunk->list);
+	chunk->nr_pages = pcpu_unit_pages;
+	region_bits = pcpu_chunk_map_bits(chunk);
 
-	chunk->map_alloc = PCPU_DFL_MAP_ALLOC;
-	chunk->map[0] = 0;
-	chunk->map[1] = pcpu_unit_size | 1;
-	chunk->map_used = 1;
-	chunk->has_reserved = false;
+	chunk->alloc_map = pcpu_mem_zalloc(BITS_TO_LONGS(region_bits) *
+					   sizeof(chunk->alloc_map[0]));
+	if (!chunk->alloc_map)
+		goto alloc_map_fail;
 
-	INIT_LIST_HEAD(&chunk->list);
-	INIT_LIST_HEAD(&chunk->map_extend_list);
-	chunk->free_size = pcpu_unit_size;
-	chunk->contig_hint = pcpu_unit_size;
+	chunk->bound_map = pcpu_mem_zalloc(BITS_TO_LONGS(region_bits + 1) *
+					   sizeof(chunk->bound_map[0]));
+	if (!chunk->bound_map)
+		goto bound_map_fail;
+
+	chunk->md_blocks = pcpu_mem_zalloc(pcpu_chunk_nr_blocks(chunk) *
+					   sizeof(chunk->md_blocks[0]));
+	if (!chunk->md_blocks)
+		goto md_blocks_fail;
+
+	pcpu_init_md_blocks(chunk);
+
+	/* init metadata */
+	chunk->contig_bits = region_bits;
+	chunk->free_bytes = chunk->nr_pages * PAGE_SIZE;
 
 	return chunk;
+
+md_blocks_fail:
+	pcpu_mem_free(chunk->bound_map);
+bound_map_fail:
+	pcpu_mem_free(chunk->alloc_map);
+alloc_map_fail:
+	pcpu_mem_free(chunk);
+
+	return NULL;
 }
 
 static void pcpu_free_chunk(struct pcpu_chunk *chunk)
 {
 	if (!chunk)
 		return;
-	pcpu_mem_free(chunk->map);
+	pcpu_mem_free(chunk->bound_map);
+	pcpu_mem_free(chunk->alloc_map);
 	pcpu_mem_free(chunk);
 }
 
@@ -748,13 +1210,17 @@ static void pcpu_free_chunk(struct pcpu_chunk *chunk)
  * @chunk: pcpu_chunk which got populated
  * @page_start: the start page
  * @page_end: the end page
+ * @for_alloc: if this is to populate for allocation
  *
  * 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)
+static void pcpu_chunk_populated(struct pcpu_chunk *chunk, int page_start,
+				 int page_end, bool for_alloc)
 {
 	int nr = page_end - page_start;
 
@@ -762,7 +1228,11 @@ static void pcpu_chunk_populated(struct pcpu_chunk *chunk,
 
 	bitmap_set(chunk->populated, page_start, nr);
 	chunk->nr_populated += nr;
-	pcpu_nr_empty_pop_pages += nr;
+
+	if (!for_alloc) {
+		chunk->nr_empty_pop_pages += nr;
+		pcpu_nr_empty_pop_pages += nr;
+	}
 }
 
 /**
@@ -784,6 +1254,7 @@ static void pcpu_chunk_depopulated(struct pcpu_chunk *chunk,
 
 	bitmap_clear(chunk->populated, page_start, nr);
 	chunk->nr_populated -= nr;
+	chunk->nr_empty_pop_pages -= nr;
 	pcpu_nr_empty_pop_pages -= nr;
 }
 
@@ -819,18 +1290,21 @@ static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai);
  * 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 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;
+	/* 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
@@ -863,19 +1337,23 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
 	struct pcpu_chunk *chunk;
 	const char *err;
 	bool is_atomic = (gfp & GFP_KERNEL) != GFP_KERNEL;
-	int occ_pages = 0;
-	int slot, off, new_alloc, cpu, ret;
+	int slot, off, cpu, ret;
 	unsigned long flags;
 	void __percpu *ptr;
+	size_t bits, bit_align;
 
 	/*
-	 * We want the lowest bit of offset available for in-use/free
-	 * indicator, so force >= 16bit alignment and make size even.
+	 * 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 < 2))
-		align = 2;
+	if (unlikely(align < PCPU_MIN_ALLOC_SIZE))
+		align = PCPU_MIN_ALLOC_SIZE;
 
-	size = ALIGN(size, 2);
+	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))) {
@@ -893,23 +1371,13 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
 	if (reserved && pcpu_reserved_chunk) {
 		chunk = pcpu_reserved_chunk;
 
-		if (size > chunk->contig_hint) {
+		off = pcpu_find_block_fit(chunk, bits, bit_align, is_atomic);
+		if (off < 0) {
 			err = "alloc from reserved chunk failed";
 			goto fail_unlock;
 		}
 
-		while ((new_alloc = pcpu_need_to_extend(chunk, is_atomic))) {
-			spin_unlock_irqrestore(&pcpu_lock, flags);
-			if (is_atomic ||
-			    pcpu_extend_area_map(chunk, new_alloc) < 0) {
-				err = "failed to extend area map of reserved chunk";
-				goto fail;
-			}
-			spin_lock_irqsave(&pcpu_lock, flags);
-		}
-
-		off = pcpu_alloc_area(chunk, size, align, is_atomic,
-				      &occ_pages);
+		off = pcpu_alloc_area(chunk, bits, bit_align, off);
 		if (off >= 0)
 			goto area_found;
 
@@ -921,31 +1389,15 @@ 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)
+			off = pcpu_find_block_fit(chunk, bits, bit_align,
+						  is_atomic);
+			if (off < 0)
 				continue;
 
-			new_alloc = pcpu_need_to_extend(chunk, is_atomic);
-			if (new_alloc) {
-				if (is_atomic)
-					continue;
-				spin_unlock_irqrestore(&pcpu_lock, flags);
-				if (pcpu_extend_area_map(chunk,
-							 new_alloc) < 0) {
-					err = "failed to extend area map";
-					goto fail;
-				}
-				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, is_atomic,
-					      &occ_pages);
+			off = pcpu_alloc_area(chunk, bits, bit_align, off);
 			if (off >= 0)
 				goto area_found;
+
 		}
 	}
 
@@ -987,30 +1439,25 @@ area_found:
 		page_start = PFN_DOWN(off);
 		page_end = PFN_UP(off + size);
 
-		pcpu_for_each_unpop_region(chunk, rs, re, page_start, page_end) {
+		pcpu_for_each_unpop_region(chunk->populated, rs, re,
+					   page_start, page_end) {
 			WARN_ON(chunk->immutable);
 
 			ret = pcpu_populate_chunk(chunk, rs, re);
 
 			spin_lock_irqsave(&pcpu_lock, flags);
 			if (ret) {
-				pcpu_free_area(chunk, off, &occ_pages);
+				pcpu_free_area(chunk, off);
 				err = "failed to populate";
 				goto fail_unlock;
 			}
-			pcpu_chunk_populated(chunk, rs, re);
+			pcpu_chunk_populated(chunk, rs, re, true);
 			spin_unlock_irqrestore(&pcpu_lock, flags);
 		}
 
 		mutex_unlock(&pcpu_alloc_mutex);
 	}
 
-	if (chunk != pcpu_reserved_chunk) {
-		spin_lock_irqsave(&pcpu_lock, flags);
-		pcpu_nr_empty_pop_pages -= occ_pages;
-		spin_unlock_irqrestore(&pcpu_lock, flags);
-	}
-
 	if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW)
 		pcpu_schedule_balance_work();
 
@@ -1128,7 +1575,6 @@ static void pcpu_balance_workfn(struct work_struct *work)
 		if (chunk == list_first_entry(free_head, struct pcpu_chunk, list))
 			continue;
 
-		list_del_init(&chunk->map_extend_list);
 		list_move(&chunk->list, &to_free);
 	}
 
@@ -1137,7 +1583,8 @@ static void pcpu_balance_workfn(struct work_struct *work)
 	list_for_each_entry_safe(chunk, next, &to_free, list) {
 		int rs, re;
 
-		pcpu_for_each_pop_region(chunk, rs, re, 0, pcpu_unit_pages) {
+		pcpu_for_each_pop_region(chunk->populated, rs, re, 0,
+					 chunk->nr_pages) {
 			pcpu_depopulate_chunk(chunk, rs, re);
 			spin_lock_irq(&pcpu_lock);
 			pcpu_chunk_depopulated(chunk, rs, re);
@@ -1146,25 +1593,6 @@ static void pcpu_balance_workfn(struct work_struct *work)
 		pcpu_destroy_chunk(chunk);
 	}
 
-	/* service chunks which requested async area map extension */
-	do {
-		int new_alloc = 0;
-
-		spin_lock_irq(&pcpu_lock);
-
-		chunk = list_first_entry_or_null(&pcpu_map_extend_chunks,
-					struct pcpu_chunk, map_extend_list);
-		if (chunk) {
-			list_del_init(&chunk->map_extend_list);
-			new_alloc = pcpu_need_to_extend(chunk, false);
-		}
-
-		spin_unlock_irq(&pcpu_lock);
-
-		if (new_alloc)
-			pcpu_extend_area_map(chunk, new_alloc);
-	} while (chunk);
-
 	/*
 	 * Ensure there are certain number of free populated pages for
 	 * atomic allocs.  Fill up from the most packed so that atomic
@@ -1194,7 +1622,7 @@ retry_pop:
 
 		spin_lock_irq(&pcpu_lock);
 		list_for_each_entry(chunk, &pcpu_slot[slot], list) {
-			nr_unpop = pcpu_unit_pages - chunk->nr_populated;
+			nr_unpop = chunk->nr_pages - chunk->nr_populated;
 			if (nr_unpop)
 				break;
 		}
@@ -1204,14 +1632,15 @@ retry_pop:
 			continue;
 
 		/* @chunk can't go away while pcpu_alloc_mutex is held */
-		pcpu_for_each_unpop_region(chunk, rs, re, 0, pcpu_unit_pages) {
+		pcpu_for_each_unpop_region(chunk->populated, rs, re, 0,
+					   chunk->nr_pages) {
 			int nr = min(re - rs, nr_to_pop);
 
 			ret = pcpu_populate_chunk(chunk, rs, rs + nr);
 			if (!ret) {
 				nr_to_pop -= nr;
 				spin_lock_irq(&pcpu_lock);
-				pcpu_chunk_populated(chunk, rs, rs + nr);
+				pcpu_chunk_populated(chunk, rs, rs + nr, false);
 				spin_unlock_irq(&pcpu_lock);
 			} else {
 				nr_to_pop = 0;
@@ -1250,7 +1679,7 @@ void free_percpu(void __percpu *ptr)
 	void *addr;
 	struct pcpu_chunk *chunk;
 	unsigned long flags;
-	int off, occ_pages;
+	int off;
 
 	if (!ptr)
 		return;
@@ -1264,13 +1693,10 @@ void free_percpu(void __percpu *ptr)
 	chunk = pcpu_chunk_addr_search(addr);
 	off = addr - chunk->base_addr;
 
-	pcpu_free_area(chunk, off, &occ_pages);
-
-	if (chunk != pcpu_reserved_chunk)
-		pcpu_nr_empty_pop_pages += occ_pages;
+	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) {
+	if (chunk->free_bytes == pcpu_unit_size) {
 		struct pcpu_chunk *pos;
 
 		list_for_each_entry(pos, &pcpu_slot[pcpu_nr_slots - 1], list)
@@ -1361,10 +1787,16 @@ phys_addr_t per_cpu_ptr_to_phys(void *addr)
 	 * The following test on unit_low/high isn't strictly
 	 * necessary but will speed up lookups of addresses which
 	 * aren't in the first chunk.
+	 *
+	 * The address check is against full chunk sizes.  pcpu_base_addr
+	 * points to the beginning of the first chunk including the
+	 * static region.  Assumes good intent as the first chunk may
+	 * not be full (ie. < pcpu_unit_pages in size).
 	 */
-	first_low = pcpu_chunk_addr(pcpu_first_chunk, pcpu_low_unit_cpu, 0);
-	first_high = pcpu_chunk_addr(pcpu_first_chunk, pcpu_high_unit_cpu,
-				     pcpu_unit_pages);
+	first_low = (unsigned long)pcpu_base_addr +
+		    pcpu_unit_page_offset(pcpu_low_unit_cpu, 0);
+	first_high = (unsigned long)pcpu_base_addr +
+		     pcpu_unit_page_offset(pcpu_high_unit_cpu, pcpu_unit_pages);
 	if ((unsigned long)addr >= first_low &&
 	    (unsigned long)addr < first_high) {
 		for_each_possible_cpu(cpu) {
@@ -1546,12 +1978,13 @@ static void pcpu_dump_alloc_info(const char *lvl,
  * 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.
+ * The first chunk will always contain a static and a dynamic region.
+ * However, the static region is not managed by any chunk.  If the first
+ * chunk also contains a reserved region, it is served by two chunks -
+ * one for the reserved region and one for the dynamic region.  They
+ * share the same vm, but use offset regions in the area allocation map.
+ * The chunk serving the dynamic region is circulated in the chunk slots
+ * and available for dynamic allocation like any other chunk.
  *
  * RETURNS:
  * 0 on success, -errno on failure.
@@ -1559,17 +1992,17 @@ static void pcpu_dump_alloc_info(const char *lvl,
 int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
 				  void *base_addr)
 {
-	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;
+	size_t size_sum = ai->static_size + ai->reserved_size + ai->dyn_size;
+	size_t static_size, dyn_size;
+	struct pcpu_chunk *chunk;
 	unsigned long *group_offsets;
 	size_t *group_sizes;
 	unsigned long *unit_off;
 	unsigned int cpu;
 	int *unit_map;
 	int group, unit, i;
+	int map_size;
+	unsigned long tmp_addr;
 
 #define PCPU_SETUP_BUG_ON(cond)	do {					\
 	if (unlikely(cond)) {						\
@@ -1592,7 +2025,12 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
 	PCPU_SETUP_BUG_ON(ai->unit_size < size_sum);
 	PCPU_SETUP_BUG_ON(offset_in_page(ai->unit_size));
 	PCPU_SETUP_BUG_ON(ai->unit_size < PCPU_MIN_UNIT_SIZE);
+	PCPU_SETUP_BUG_ON(!IS_ALIGNED(ai->unit_size, PCPU_BITMAP_BLOCK_SIZE));
 	PCPU_SETUP_BUG_ON(ai->dyn_size < PERCPU_DYNAMIC_EARLY_SIZE);
+	PCPU_SETUP_BUG_ON(!ai->dyn_size);
+	PCPU_SETUP_BUG_ON(!IS_ALIGNED(ai->reserved_size, PCPU_MIN_ALLOC_SIZE));
+	PCPU_SETUP_BUG_ON(!(IS_ALIGNED(PCPU_BITMAP_BLOCK_SIZE, PAGE_SIZE) ||
+			    IS_ALIGNED(PAGE_SIZE, PCPU_BITMAP_BLOCK_SIZE)));
 	PCPU_SETUP_BUG_ON(pcpu_verify_alloc_info(ai) < 0);
 
 	/* process group information and build config tables accordingly */
@@ -1671,64 +2109,41 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
 		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).
+	 * The end of the static region needs to be aligned with the
+	 * minimum allocation size as this offsets the reserved and
+	 * dynamic region.  The first chunk ends page aligned by
+	 * expanding the dynamic region, therefore the dynamic region
+	 * can be shrunk to compensate while still staying above the
+	 * configured sizes.
 	 */
-	schunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0);
-	INIT_LIST_HEAD(&schunk->list);
-	INIT_LIST_HEAD(&schunk->map_extend_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);
-	schunk->nr_populated = pcpu_unit_pages;
+	static_size = ALIGN(ai->static_size, PCPU_MIN_ALLOC_SIZE);
+	dyn_size = ai->dyn_size - (static_size - ai->static_size);
 
-	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[0] = 1;
-	schunk->map[1] = ai->static_size;
-	schunk->map_used = 1;
-	if (schunk->free_size)
-		schunk->map[++schunk->map_used] = ai->static_size + schunk->free_size;
-	schunk->map[schunk->map_used] |= 1;
-	schunk->has_reserved = true;
+	/*
+	 * Initialize first chunk.
+	 * If the reserved_size is non-zero, this initializes the reserved
+	 * chunk.  If the reserved_size is zero, the reserved chunk is NULL
+	 * and the dynamic region is initialized here.  The first chunk,
+	 * pcpu_first_chunk, will always point to the chunk that serves
+	 * the dynamic region.
+	 */
+	tmp_addr = (unsigned long)base_addr + static_size;
+	map_size = ai->reserved_size ?: dyn_size;
+	chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);
 
 	/* init dynamic chunk if necessary */
-	if (dyn_size) {
-		dchunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0);
-		INIT_LIST_HEAD(&dchunk->list);
-		INIT_LIST_HEAD(&dchunk->map_extend_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->nr_populated = pcpu_unit_pages;
-
-		dchunk->contig_hint = dchunk->free_size = dyn_size;
-		dchunk->map[0] = 1;
-		dchunk->map[1] = pcpu_reserved_chunk_limit;
-		dchunk->map[2] = (pcpu_reserved_chunk_limit + dchunk->free_size) | 1;
-		dchunk->map_used = 2;
-		dchunk->has_reserved = true;
+	if (ai->reserved_size) {
+		pcpu_reserved_chunk = chunk;
+
+		tmp_addr = (unsigned long)base_addr + static_size +
+			   ai->reserved_size;
+		map_size = dyn_size;
+		chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);
 	}
 
 	/* link the first chunk in */
-	pcpu_first_chunk = dchunk ?: schunk;
-	pcpu_nr_empty_pop_pages +=
-		pcpu_count_occupied_pages(pcpu_first_chunk, 1);
+	pcpu_first_chunk = chunk;
+	pcpu_nr_empty_pop_pages = pcpu_first_chunk->nr_empty_pop_pages;
 	pcpu_chunk_relocate(pcpu_first_chunk, -1);
 
 	pcpu_stats_chunk_alloc();
@@ -1842,6 +2257,7 @@ static struct pcpu_alloc_info * __init pcpu_build_alloc_info(
 	 */
 	min_unit_size = max_t(size_t, size_sum, PCPU_MIN_UNIT_SIZE);
 
+	/* determine the maximum # of units that can fit in an allocation */
 	alloc_size = roundup(min_unit_size, atom_size);
 	upa = alloc_size / min_unit_size;
 	while (alloc_size % upa || (offset_in_page(alloc_size / upa)))
@@ -1868,9 +2284,9 @@ static struct pcpu_alloc_info * __init pcpu_build_alloc_info(
 	}
 
 	/*
-	 * Expand unit size until address space usage goes over 75%
-	 * and then as much as possible without using more address
-	 * space.
+	 * Wasted space is caused by a ratio imbalance of upa to group_cnt.
+	 * Expand the unit_size until we use >= 75% of the units allocated.
+	 * Related to atom_size, which could be much larger than the unit_size.
 	 */
 	last_allocs = INT_MAX;
 	for (upa = max_upa; upa; upa--) {
@@ -2298,36 +2714,6 @@ void __init setup_per_cpu_areas(void)
 
 #endif	/* CONFIG_SMP */
 
-/*
- * 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_zalloc(size);
-		BUG_ON(!map);
-
-		spin_lock_irqsave(&pcpu_lock, flags);
-		memcpy(map, chunk->map, size);
-		chunk->map = map;
-		spin_unlock_irqrestore(&pcpu_lock, flags);
-	}
-}
-
 /*
  * Percpu allocator is initialized early during boot when neither slab or
  * workqueue is available.  Plug async management until everything is up