1 files changed, 890 insertions, 0 deletions

diff --git a/mm/percpu.c b/mm/percpu.c
new file mode 100644
index 000000000000..4617d97e877c
--- /dev/null
+++ b/mm/percpu.c
@@ -0,0 +1,890 @@
+/*
+ * linux/mm/percpu.c - percpu memory allocator
+ *
+ * Copyright (C) 2009           SUSE Linux Products GmbH
+ * Copyright (C) 2009           Tejun Heo <tj@kernel.org>
+ *
+ * This file is released under the GPLv2.
+ *
+ * This is percpu allocator which can handle both static and dynamic
+ * areas.  Percpu areas are allocated in chunks in vmalloc area.  Each
+ * chunk is consisted of num_possible_cpus() 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.  ie. in vmalloc area
+ *
+ *  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.  Percpu access can be done by configuring
+ * percpu base registers UNIT_SIZE apart.
+ *
+ * There are usually many small percpu allocations many of them as
+ * small as 4 bytes.  The allocator organizes chunks into lists
+ * according to free size and tries to allocate from the fullest one.
+ * Each chunk keeps the maximum contiguous area size hint which is
+ * guaranteed to be eqaul to or larger than the maximum contiguous
+ * area in the chunk.  This helps the allocator not to iterate the
+ * chunk maps unnecessarily.
+ *
+ * Allocation state in each chunk is kept using an array of integers
+ * on chunk->map.  A positive value in the map represents a free
+ * region and negative allocated.  Allocation inside a chunk is done
+ * by scanning this map sequentially and serving the first matching
+ * entry.  This is mostly copied from the percpu_modalloc() allocator.
+ * Chunks are also linked into a rb tree to ease address to chunk
+ * mapping during free.
+ *
+ * To use this allocator, arch code should do the followings.
+ *
+ * - define CONFIG_HAVE_DYNAMIC_PER_CPU_AREA
+ *
+ * - define __addr_to_pcpu_ptr() and __pcpu_ptr_to_addr() to translate
+ *   regular address to percpu pointer and back
+ *
+ * - use pcpu_setup_static() during percpu area initialization to
+ *   setup kernel static percpu area
+ */
+
+#include <linux/bitmap.h>
+#include <linux/bootmem.h>
+#include <linux/list.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/percpu.h>
+#include <linux/pfn.h>
+#include <linux/rbtree.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+
+#include <asm/cacheflush.h>
+#include <asm/tlbflush.h>
+
+#define PCPU_MIN_UNIT_PAGES_SHIFT       4       /* also max alloc size */
+#define PCPU_SLOT_BASE_SHIFT            5       /* 1-31 shares the same slot */
+#define PCPU_DFL_MAP_ALLOC              16      /* start a map with 16 ents */
+
+struct pcpu_chunk {
+        struct list_head        list;           /* linked to pcpu_slot lists */
+        struct rb_node          rb_node;        /* key is chunk->vm->addr */
+        int                     free_size;      /* free bytes in the chunk */
+        int                     contig_hint;    /* max contiguous size hint */
+        struct vm_struct        *vm;            /* mapped vmalloc region */
+        int                     map_used;       /* # of map entries used */
+        int                     map_alloc;      /* # of map entries allocated */
+        int                     *map;           /* allocation map */
+        struct page             *page[];        /* #cpus * UNIT_PAGES */
+};
+
+static int pcpu_unit_pages_shift;
+static int pcpu_unit_pages;
+static int pcpu_unit_shift;
+static int pcpu_unit_size;
+static int pcpu_chunk_size;
+static int pcpu_nr_slots;
+static size_t pcpu_chunk_struct_size;
+
+/* the address of the first chunk which starts with the kernel static area */
+void *pcpu_base_addr;
+EXPORT_SYMBOL_GPL(pcpu_base_addr);
+
+/* the size of kernel static area */
+static int pcpu_static_size;
+
+/*
+ * One mutex to rule them all.
+ *
+ * The following mutex is grabbed in the outermost public alloc/free
+ * interface functions and released only when the operation is
+ * complete.  As such, every function in this file other than the
+ * outermost functions are called under pcpu_mutex.
+ *
+ * It can easily be switched to use spinlock such that only the area
+ * allocation and page population commit are protected with it doing
+ * actual [de]allocation without holding any lock.  However, given
+ * what this allocator does, I think it's better to let them run
+ * sequentially.
+ */
+static DEFINE_MUTEX(pcpu_mutex);
+
+static struct list_head *pcpu_slot;             /* chunk list slots */
+static struct rb_root pcpu_addr_root = RB_ROOT; /* chunks by address */
+
+static int pcpu_size_to_slot(int size)
+{
+        int highbit = fls(size);
+        return max(highbit - PCPU_SLOT_BASE_SHIFT + 2, 1);
+}
+
+static int pcpu_chunk_slot(const struct pcpu_chunk *chunk)
+{
+        if (chunk->free_size < sizeof(int) || chunk->contig_hint < sizeof(int))
+                return 0;
+
+        return pcpu_size_to_slot(chunk->free_size);
+}
+
+static int pcpu_page_idx(unsigned int cpu, int page_idx)
+{
+        return (cpu << pcpu_unit_pages_shift) + page_idx;
+}
+
+static struct page **pcpu_chunk_pagep(struct pcpu_chunk *chunk,
+                                      unsigned int cpu, int page_idx)
+{
+        return &chunk->page[pcpu_page_idx(cpu, page_idx)];
+}
+
+static unsigned long pcpu_chunk_addr(struct pcpu_chunk *chunk,
+                                     unsigned int cpu, int page_idx)
+{
+        return (unsigned long)chunk->vm->addr +
+                (pcpu_page_idx(cpu, page_idx) << PAGE_SHIFT);
+}
+
+static bool pcpu_chunk_page_occupied(struct pcpu_chunk *chunk,
+                                     int page_idx)
+{
+        return *pcpu_chunk_pagep(chunk, 0, page_idx) != NULL;
+}
+
+/**
+ * pcpu_realloc - versatile realloc
+ * @p: the current pointer (can be NULL for new allocations)
+ * @size: the current size (can be 0 for new allocations)
+ * @new_size: the wanted new size (can be 0 for free)
+ *
+ * More robust realloc which can be used to allocate, resize or free a
+ * memory area of arbitrary size.  If the needed size goes over
+ * PAGE_SIZE, kernel VM is used.
+ *
+ * RETURNS:
+ * The new pointer on success, NULL on failure.
+ */
+static void *pcpu_realloc(void *p, size_t size, size_t new_size)
+{
+        void *new;
+
+        if (new_size <= PAGE_SIZE)
+                new = kmalloc(new_size, GFP_KERNEL);
+        else
+                new = vmalloc(new_size);
+        if (new_size && !new)
+                return NULL;
+
+        memcpy(new, p, min(size, new_size));
+        if (new_size > size)
+                memset(new + size, 0, new_size - size);
+
+        if (size <= PAGE_SIZE)
+                kfree(p);
+        else
+                vfree(p);
+
+        return new;
+}
+
+/**
+ * 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.
+ */
+static void pcpu_chunk_relocate(struct pcpu_chunk *chunk, int oslot)
+{
+        int nslot = pcpu_chunk_slot(chunk);
+
+        if (oslot != nslot) {
+                if (oslot < nslot)
+                        list_move(&chunk->list, &pcpu_slot[nslot]);
+                else
+                        list_move_tail(&chunk->list, &pcpu_slot[nslot]);
+        }
+}
+
+static struct rb_node **pcpu_chunk_rb_search(void *addr,
+                                             struct rb_node **parentp)
+{
+        struct rb_node **p = &pcpu_addr_root.rb_node;
+        struct rb_node *parent = NULL;
+        struct pcpu_chunk *chunk;
+
+        while (*p) {
+                parent = *p;
+                chunk = rb_entry(parent, struct pcpu_chunk, rb_node);
+
+                if (addr < chunk->vm->addr)
+                        p = &(*p)->rb_left;
+                else if (addr > chunk->vm->addr)
+                        p = &(*p)->rb_right;
+                else
+                        break;
+        }
+
+        if (parentp)
+                *parentp = parent;
+        return p;
+}
+
+/**
+ * pcpu_chunk_addr_search - search for chunk containing specified address
+ * @addr: address to search for
+ *
+ * Look for chunk which might contain @addr.  More specifically, it
+ * searchs for the chunk with the highest start address which isn't
+ * beyond @addr.
+ *
+ * RETURNS:
+ * The address of the found chunk.
+ */
+static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
+{
+        struct rb_node *n, *parent;
+        struct pcpu_chunk *chunk;
+
+        n = *pcpu_chunk_rb_search(addr, &parent);
+        if (!n) {
+                /* no exactly matching chunk, the parent is the closest */
+                n = parent;
+                BUG_ON(!n);
+        }
+        chunk = rb_entry(n, struct pcpu_chunk, rb_node);
+
+        if (addr < chunk->vm->addr) {
+                /* the parent was the next one, look for the previous one */
+                n = rb_prev(n);
+                BUG_ON(!n);
+                chunk = rb_entry(n, struct pcpu_chunk, rb_node);
+        }
+
+        return chunk;
+}
+
+/**
+ * pcpu_chunk_addr_insert - insert chunk into address rb tree
+ * @new: chunk to insert
+ *
+ * Insert @new into address rb tree.
+ */
+static void pcpu_chunk_addr_insert(struct pcpu_chunk *new)
+{
+        struct rb_node **p, *parent;
+
+        p = pcpu_chunk_rb_search(new->vm->addr, &parent);
+        BUG_ON(*p);
+        rb_link_node(&new->rb_node, parent, p);
+        rb_insert_color(&new->rb_node, &pcpu_addr_root);
+}
+
+/**
+ * pcpu_split_block - split a map block
+ * @chunk: chunk of interest
+ * @i: index of map block to split
+ * @head: head size (can be 0)
+ * @tail: tail size (can be 0)
+ *
+ * Split the @i'th map block into two or three blocks.  If @head is
+ * non-zero, @head bytes block is inserted before block @i moving it
+ * to @i+1 and reducing its size by @head bytes.
+ *
+ * If @tail is non-zero, the target block, which can be @i or @i+1
+ * depending on @head, is reduced by @tail bytes and @tail byte block
+ * is inserted after the target block.
+ *
+ * RETURNS:
+ * 0 on success, -errno on failure.
+ */
+static int pcpu_split_block(struct pcpu_chunk *chunk, int i, int head, int tail)
+{
+        int nr_extra = !!head + !!tail;
+        int target = chunk->map_used + nr_extra;
+
+        /* reallocation required? */
+        if (chunk->map_alloc < target) {
+                int new_alloc = chunk->map_alloc;
+                int *new;
+
+                while (new_alloc < target)
+                        new_alloc *= 2;
+
+                new = pcpu_realloc(chunk->map,
+                                   chunk->map_alloc * sizeof(new[0]),
+                                   new_alloc * sizeof(new[0]));
+                if (!new)
+                        return -ENOMEM;
+
+                chunk->map_alloc = new_alloc;
+                chunk->map = new;
+        }
+
+        /* insert a new subblock */
+        memmove(&chunk->map[i + nr_extra], &chunk->map[i],
+                sizeof(chunk->map[0]) * (chunk->map_used - i));
+        chunk->map_used += nr_extra;
+
+        if (head) {
+                chunk->map[i + 1] = chunk->map[i] - head;
+                chunk->map[i++] = head;
+        }
+        if (tail) {
+                chunk->map[i++] -= tail;
+                chunk->map[i] = tail;
+        }
+        return 0;
+}
+
+/**
+ * pcpu_alloc_area - allocate area from a pcpu_chunk
+ * @chunk: chunk of interest
+ * @size: wanted size
+ * @align: wanted align
+ *
+ * Try to allocate @size bytes area aligned at @align from @chunk.
+ * Note that this function only allocates the offset.  It doesn't
+ * populate or map the area.
+ *
+ * RETURNS:
+ * Allocated offset in @chunk on success, -errno on failure.
+ */
+static int pcpu_alloc_area(struct pcpu_chunk *chunk, int size, int align)
+{
+        int oslot = pcpu_chunk_slot(chunk);
+        int max_contig = 0;
+        int i, off;
+
+        /*
+         * The static chunk initially doesn't have map attached
+         * because kmalloc wasn't available during init.  Give it one.
+         */
+        if (unlikely(!chunk->map)) {
+                chunk->map = pcpu_realloc(NULL, 0,
+                                PCPU_DFL_MAP_ALLOC * sizeof(chunk->map[0]));
+                if (!chunk->map)
+                        return -ENOMEM;
+
+                chunk->map_alloc = PCPU_DFL_MAP_ALLOC;
+                chunk->map[chunk->map_used++] = -pcpu_static_size;
+                if (chunk->free_size)
+                        chunk->map[chunk->map_used++] = chunk->free_size;
+        }
+
+        for (i = 0, off = 0; i < chunk->map_used; off += abs(chunk->map[i++])) {
+                bool is_last = i + 1 == chunk->map_used;
+                int head, tail;
+
+                /* extra for alignment requirement */
+                head = ALIGN(off, align) - off;
+                BUG_ON(i == 0 && head != 0);
+
+                if (chunk->map[i] < 0)
+                        continue;
+                if (chunk->map[i] < head + size) {
+                        max_contig = max(chunk->map[i], max_contig);
+                        continue;
+                }
+
+                /*
+                 * If head is small or the previous block is free,
+                 * merge'em.  Note that 'small' is defined as smaller
+                 * than sizeof(int), which is very small but isn't too
+                 * uncommon for percpu allocations.
+                 */
+                if (head && (head < sizeof(int) || chunk->map[i - 1] > 0)) {
+                        if (chunk->map[i - 1] > 0)
+                                chunk->map[i - 1] += head;
+                        else {
+                                chunk->map[i - 1] -= head;
+                                chunk->free_size -= head;
+                        }
+                        chunk->map[i] -= head;
+                        off += head;
+                        head = 0;
+                }
+
+                /* if tail is small, just keep it around */
+                tail = chunk->map[i] - head - size;
+                if (tail < sizeof(int))
+                        tail = 0;
+
+                /* split if warranted */
+                if (head || tail) {
+                        if (pcpu_split_block(chunk, i, head, tail))
+                                return -ENOMEM;
+                        if (head) {
+                                i++;
+                                off += head;
+                                max_contig = max(chunk->map[i - 1], max_contig);
+                        }
+                        if (tail)
+                                max_contig = max(chunk->map[i + 1], max_contig);
+                }
+
+                /* update hint and mark allocated */
+                if (is_last)
+                        chunk->contig_hint = max_contig; /* fully scanned */
+                else
+                        chunk->contig_hint = max(chunk->contig_hint,
+                                                 max_contig);
+
+                chunk->free_size -= chunk->map[i];
+                chunk->map[i] = -chunk->map[i];
+
+                pcpu_chunk_relocate(chunk, oslot);
+                return off;
+        }
+
+        chunk->contig_hint = max_contig;        /* fully scanned */
+        pcpu_chunk_relocate(chunk, oslot);
+
+        /*
+         * Tell the upper layer that this chunk has no area left.
+         * Note that this is not an error condition but a notification
+         * to upper layer that it needs to look at other chunks.
+         * -ENOSPC is chosen as it isn't used in memory subsystem and
+         * matches the meaning in a way.
+         */
+        return -ENOSPC;
+}
+
+/**
+ * pcpu_free_area - free area to a pcpu_chunk
+ * @chunk: chunk of interest
+ * @freeme: offset of area to free
+ *
+ * Free area starting from @freeme to @chunk.  Note that this function
+ * only modifies the allocation map.  It doesn't depopulate or unmap
+ * the area.
+ */
+static void pcpu_free_area(struct pcpu_chunk *chunk, int freeme)
+{
+        int oslot = pcpu_chunk_slot(chunk);
+        int i, off;
+
+        for (i = 0, off = 0; i < chunk->map_used; off += abs(chunk->map[i++]))
+                if (off == freeme)
+                        break;
+        BUG_ON(off != freeme);
+        BUG_ON(chunk->map[i] > 0);
+
+        chunk->map[i] = -chunk->map[i];
+        chunk->free_size += chunk->map[i];
+
+        /* merge with previous? */
+        if (i > 0 && chunk->map[i - 1] >= 0) {
+                chunk->map[i - 1] += chunk->map[i];
+                chunk->map_used--;
+                memmove(&chunk->map[i], &chunk->map[i + 1],
+                        (chunk->map_used - i) * sizeof(chunk->map[0]));
+                i--;
+        }
+        /* merge with next? */
+        if (i + 1 < chunk->map_used && chunk->map[i + 1] >= 0) {
+                chunk->map[i] += chunk->map[i + 1];
+                chunk->map_used--;
+                memmove(&chunk->map[i + 1], &chunk->map[i + 2],
+                        (chunk->map_used - (i + 1)) * sizeof(chunk->map[0]));
+        }
+
+        chunk->contig_hint = max(chunk->map[i], chunk->contig_hint);
+        pcpu_chunk_relocate(chunk, oslot);
+}
+
+/**
+ * pcpu_unmap - unmap pages out of a pcpu_chunk
+ * @chunk: chunk of interest
+ * @page_start: page index of the first page to unmap
+ * @page_end: page index of the last page to unmap + 1
+ * @flush: whether to flush cache and tlb or not
+ *
+ * For each cpu, unmap pages [@page_start,@page_end) out of @chunk.
+ * If @flush is true, vcache is flushed before unmapping and tlb
+ * after.
+ */
+static void pcpu_unmap(struct pcpu_chunk *chunk, int page_start, int page_end,
+                       bool flush)
+{
+        unsigned int last = num_possible_cpus() - 1;
+        unsigned int cpu;
+
+        /*
+         * Each flushing trial can be very expensive, issue flush on
+         * the whole region at once rather than doing it for each cpu.
+         * This could be an overkill but is more scalable.
+         */
+        if (flush)
+                flush_cache_vunmap(pcpu_chunk_addr(chunk, 0, page_start),
+                                   pcpu_chunk_addr(chunk, last, page_end));
+
+        for_each_possible_cpu(cpu)
+                unmap_kernel_range_noflush(
+                                pcpu_chunk_addr(chunk, cpu, page_start),
+                                (page_end - page_start) << PAGE_SHIFT);
+
+        /* ditto as flush_cache_vunmap() */
+        if (flush)
+                flush_tlb_kernel_range(pcpu_chunk_addr(chunk, 0, page_start),
+                                       pcpu_chunk_addr(chunk, last, page_end));
+}
+
+/**
+ * pcpu_depopulate_chunk - depopulate and unmap an area of a pcpu_chunk
+ * @chunk: chunk to depopulate
+ * @off: offset to the area to depopulate
+ * @size: size of the area to depopulate
+ * @flush: whether to flush cache and tlb or not
+ *
+ * For each cpu, depopulate and unmap pages [@page_start,@page_end)
+ * from @chunk.  If @flush is true, vcache is flushed before unmapping
+ * and tlb after.
+ */
+static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk, size_t off,
+                                  size_t size, bool flush)
+{
+        int page_start = PFN_DOWN(off);
+        int page_end = PFN_UP(off + size);
+        int unmap_start = -1;
+        int uninitialized_var(unmap_end);
+        unsigned int cpu;
+        int i;
+
+        for (i = page_start; i < page_end; i++) {
+                for_each_possible_cpu(cpu) {
+                        struct page **pagep = pcpu_chunk_pagep(chunk, cpu, i);
+
+                        if (!*pagep)
+                                continue;
+
+                        __free_page(*pagep);
+
+                        /*
+                         * If it's partial depopulation, it might get
+                         * populated or depopulated again.  Mark the
+                         * page gone.
+                         */
+                        *pagep = NULL;
+
+                        unmap_start = unmap_start < 0 ? i : unmap_start;
+                        unmap_end = i + 1;
+                }
+        }
+
+        if (unmap_start >= 0)
+                pcpu_unmap(chunk, unmap_start, unmap_end, flush);
+}
+
+/**
+ * pcpu_map - map pages into a pcpu_chunk
+ * @chunk: chunk of interest
+ * @page_start: page index of the first page to map
+ * @page_end: page index of the last page to map + 1
+ *
+ * For each cpu, map pages [@page_start,@page_end) into @chunk.
+ * vcache is flushed afterwards.
+ */
+static int pcpu_map(struct pcpu_chunk *chunk, int page_start, int page_end)
+{
+        unsigned int last = num_possible_cpus() - 1;
+        unsigned int cpu;
+        int err;
+
+        for_each_possible_cpu(cpu) {
+                err = map_kernel_range_noflush(
+                                pcpu_chunk_addr(chunk, cpu, page_start),
+                                (page_end - page_start) << PAGE_SHIFT,
+                                PAGE_KERNEL,
+                                pcpu_chunk_pagep(chunk, cpu, page_start));
+                if (err < 0)
+                        return err;
+        }
+
+        /* flush at once, please read comments in pcpu_unmap() */
+        flush_cache_vmap(pcpu_chunk_addr(chunk, 0, page_start),
+                         pcpu_chunk_addr(chunk, last, page_end));
+        return 0;
+}
+
+/**
+ * pcpu_populate_chunk - populate and map an area of a pcpu_chunk
+ * @chunk: chunk of interest
+ * @off: offset to the area to populate
+ * @size: size of the area to populate
+ *
+ * For each cpu, populate and map pages [@page_start,@page_end) into
+ * @chunk.  The area is cleared on return.
+ */
+static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size)
+{
+        const gfp_t alloc_mask = GFP_KERNEL | __GFP_HIGHMEM | __GFP_COLD;
+        int page_start = PFN_DOWN(off);
+        int page_end = PFN_UP(off + size);
+        int map_start = -1;
+        int map_end;
+        unsigned int cpu;
+        int i;
+
+        for (i = page_start; i < page_end; i++) {
+                if (pcpu_chunk_page_occupied(chunk, i)) {
+                        if (map_start >= 0) {
+                                if (pcpu_map(chunk, map_start, map_end))
+                                        goto err;
+                                map_start = -1;
+                        }
+                        continue;
+                }
+
+                map_start = map_start < 0 ? i : map_start;
+                map_end = i + 1;
+
+                for_each_possible_cpu(cpu) {
+                        struct page **pagep = pcpu_chunk_pagep(chunk, cpu, i);
+
+                        *pagep = alloc_pages_node(cpu_to_node(cpu),
+                                                  alloc_mask, 0);
+                        if (!*pagep)
+                                goto err;
+                }
+        }
+
+        if (map_start >= 0 && pcpu_map(chunk, map_start, map_end))
+                goto err;
+
+        for_each_possible_cpu(cpu)
+                memset(chunk->vm->addr + (cpu << pcpu_unit_shift) + off, 0,
+                       size);
+
+        return 0;
+err:
+        /* likely under heavy memory pressure, give memory back */
+        pcpu_depopulate_chunk(chunk, off, size, true);
+        return -ENOMEM;
+}
+
+static void free_pcpu_chunk(struct pcpu_chunk *chunk)
+{
+        if (!chunk)
+                return;
+        if (chunk->vm)
+                free_vm_area(chunk->vm);
+        pcpu_realloc(chunk->map, chunk->map_alloc * sizeof(chunk->map[0]), 0);
+        kfree(chunk);
+}
+
+static struct pcpu_chunk *alloc_pcpu_chunk(void)
+{
+        struct pcpu_chunk *chunk;
+
+        chunk = kzalloc(pcpu_chunk_struct_size, GFP_KERNEL);
+        if (!chunk)
+                return NULL;
+
+        chunk->map = pcpu_realloc(NULL, 0,
+                                  PCPU_DFL_MAP_ALLOC * sizeof(chunk->map[0]));
+        chunk->map_alloc = PCPU_DFL_MAP_ALLOC;
+        chunk->map[chunk->map_used++] = pcpu_unit_size;
+
+        chunk->vm = get_vm_area(pcpu_chunk_size, GFP_KERNEL);
+        if (!chunk->vm) {
+                free_pcpu_chunk(chunk);
+                return NULL;
+        }
+
+        INIT_LIST_HEAD(&chunk->list);
+        chunk->free_size = pcpu_unit_size;
+        chunk->contig_hint = pcpu_unit_size;
+
+        return chunk;
+}
+
+/**
+ * __alloc_percpu - allocate percpu area
+ * @size: size of area to allocate
+ * @align: alignment of area (max PAGE_SIZE)
+ *
+ * Allocate percpu area of @size bytes aligned at @align.  Might
+ * sleep.  Might trigger writeouts.
+ *
+ * RETURNS:
+ * Percpu pointer to the allocated area on success, NULL on failure.
+ */
+void *__alloc_percpu(size_t size, size_t align)
+{
+        void *ptr = NULL;
+        struct pcpu_chunk *chunk;
+        int slot, off;
+
+        if (unlikely(!size || size > PAGE_SIZE << PCPU_MIN_UNIT_PAGES_SHIFT ||
+                     align > PAGE_SIZE)) {
+                WARN(true, "illegal size (%zu) or align (%zu) for "
+                     "percpu allocation\n", size, align);
+                return NULL;
+        }
+
+        mutex_lock(&pcpu_mutex);
+
+        /* allocate area */
+        for (slot = pcpu_size_to_slot(size); slot < pcpu_nr_slots; slot++) {
+                list_for_each_entry(chunk, &pcpu_slot[slot], list) {
+                        if (size > chunk->contig_hint)
+                                continue;
+                        off = pcpu_alloc_area(chunk, size, align);
+                        if (off >= 0)
+                                goto area_found;
+                        if (off != -ENOSPC)
+                                goto out_unlock;
+                }
+        }
+
+        /* hmmm... no space left, create a new chunk */
+        chunk = alloc_pcpu_chunk();
+        if (!chunk)
+                goto out_unlock;
+        pcpu_chunk_relocate(chunk, -1);
+        pcpu_chunk_addr_insert(chunk);
+
+        off = pcpu_alloc_area(chunk, size, align);
+        if (off < 0)
+                goto out_unlock;
+
+area_found:
+        /* populate, map and clear the area */
+        if (pcpu_populate_chunk(chunk, off, size)) {
+                pcpu_free_area(chunk, off);
+                goto out_unlock;
+        }
+
+        ptr = __addr_to_pcpu_ptr(chunk->vm->addr + off);
+out_unlock:
+        mutex_unlock(&pcpu_mutex);
+        return ptr;
+}
+EXPORT_SYMBOL_GPL(__alloc_percpu);
+
+static void pcpu_kill_chunk(struct pcpu_chunk *chunk)
+{
+        pcpu_depopulate_chunk(chunk, 0, pcpu_unit_size, false);
+        list_del(&chunk->list);
+        rb_erase(&chunk->rb_node, &pcpu_addr_root);
+        free_pcpu_chunk(chunk);
+}
+
+/**
+ * free_percpu - free percpu area
+ * @ptr: pointer to area to free
+ *
+ * Free percpu area @ptr.  Might sleep.
+ */
+void free_percpu(void *ptr)
+{
+        void *addr = __pcpu_ptr_to_addr(ptr);
+        struct pcpu_chunk *chunk;
+        int off;
+
+        if (!ptr)
+                return;
+
+        mutex_lock(&pcpu_mutex);
+
+        chunk = pcpu_chunk_addr_search(addr);
+        off = addr - chunk->vm->addr;
+
+        pcpu_free_area(chunk, off);
+
+        /* the chunk became fully free, kill one if there are other free ones */
+        if (chunk->free_size == pcpu_unit_size) {
+                struct pcpu_chunk *pos;
+
+                list_for_each_entry(pos,
+                                    &pcpu_slot[pcpu_chunk_slot(chunk)], list)
+                        if (pos != chunk) {
+                                pcpu_kill_chunk(pos);
+                                break;
+                        }
+        }
+
+        mutex_unlock(&pcpu_mutex);
+}
+EXPORT_SYMBOL_GPL(free_percpu);
+
+/**
+ * pcpu_setup_static - initialize kernel static percpu area
+ * @populate_pte_fn: callback to allocate pagetable
+ * @pages: num_possible_cpus() * PFN_UP(cpu_size) pages
+ *
+ * Initialize kernel static percpu area.  The caller should allocate
+ * all the necessary pages and pass them in @pages.
+ * @populate_pte_fn() is called on each page to be used for percpu
+ * mapping and is responsible for making sure all the necessary page
+ * tables for the page is allocated.
+ *
+ * RETURNS:
+ * The determined pcpu_unit_size which can be used to initialize
+ * percpu access.
+ */
+size_t __init pcpu_setup_static(pcpu_populate_pte_fn_t populate_pte_fn,
+                                struct page **pages, size_t cpu_size)
+{
+        static struct vm_struct static_vm;
+        struct pcpu_chunk *static_chunk;
+        int nr_cpu_pages = DIV_ROUND_UP(cpu_size, PAGE_SIZE);
+        unsigned int cpu;
+        int err, i;
+
+        pcpu_unit_pages_shift = max_t(int, PCPU_MIN_UNIT_PAGES_SHIFT,
+                                      order_base_2(cpu_size) - PAGE_SHIFT);
+
+        pcpu_static_size = cpu_size;
+        pcpu_unit_pages = 1 << pcpu_unit_pages_shift;
+        pcpu_unit_shift = PAGE_SHIFT + pcpu_unit_pages_shift;
+        pcpu_unit_size = 1 << pcpu_unit_shift;
+        pcpu_chunk_size = num_possible_cpus() * pcpu_unit_size;
+        pcpu_nr_slots = pcpu_size_to_slot(pcpu_unit_size) + 1;
+        pcpu_chunk_struct_size = sizeof(struct pcpu_chunk)
+                + (1 << pcpu_unit_pages_shift) * sizeof(struct page *);
+
+        /* allocate chunk slots */
+        pcpu_slot = alloc_bootmem(pcpu_nr_slots * sizeof(pcpu_slot[0]));
+        for (i = 0; i < pcpu_nr_slots; i++)
+                INIT_LIST_HEAD(&pcpu_slot[i]);
+
+        /* init and register vm area */
+        static_vm.flags = VM_ALLOC;
+        static_vm.size = pcpu_chunk_size;
+        vm_area_register_early(&static_vm);
+
+        /* init static_chunk */
+        static_chunk = alloc_bootmem(pcpu_chunk_struct_size);
+        INIT_LIST_HEAD(&static_chunk->list);
+        static_chunk->vm = &static_vm;
+        static_chunk->free_size = pcpu_unit_size - pcpu_static_size;
+        static_chunk->contig_hint = static_chunk->free_size;
+
+        /* assign pages and map them */
+        for_each_possible_cpu(cpu) {
+                for (i = 0; i < nr_cpu_pages; i++) {
+                        *pcpu_chunk_pagep(static_chunk, cpu, i) = *pages++;
+                        populate_pte_fn(pcpu_chunk_addr(static_chunk, cpu, i));
+                }
+        }
+
+        err = pcpu_map(static_chunk, 0, nr_cpu_pages);
+        if (err)
+                panic("failed to setup static percpu area, err=%d\n", err);
+
+        /* link static_chunk in */
+        pcpu_chunk_relocate(static_chunk, -1);
+        pcpu_chunk_addr_insert(static_chunk);
+
+        /* we're done */
+        pcpu_base_addr = (void *)pcpu_chunk_addr(static_chunk, 0, 0);
+        return pcpu_unit_size;
+}