linux/mm/percpu-km.c
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   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * mm/percpu-km.c - kernel memory based chunk allocation
   4 *
   5 * Copyright (C) 2010           SUSE Linux Products GmbH
   6 * Copyright (C) 2010           Tejun Heo <tj@kernel.org>
   7 *
   8 * Chunks are allocated as a contiguous kernel memory using gfp
   9 * allocation.  This is to be used on nommu architectures.
  10 *
  11 * To use percpu-km,
  12 *
  13 * - define CONFIG_NEED_PER_CPU_KM from the arch Kconfig.
  14 *
  15 * - CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK must not be defined.  It's
  16 *   not compatible with PER_CPU_KM.  EMBED_FIRST_CHUNK should work
  17 *   fine.
  18 *
  19 * - NUMA is not supported.  When setting up the first chunk,
  20 *   @cpu_distance_fn should be NULL or report all CPUs to be nearer
  21 *   than or at LOCAL_DISTANCE.
  22 *
  23 * - It's best if the chunk size is power of two multiple of
  24 *   PAGE_SIZE.  Because each chunk is allocated as a contiguous
  25 *   kernel memory block using alloc_pages(), memory will be wasted if
  26 *   chunk size is not aligned.  percpu-km code will whine about it.
  27 */
  28
  29#if defined(CONFIG_SMP) && defined(CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK)
  30#error "contiguous percpu allocation is incompatible with paged first chunk"
  31#endif
  32
  33#include <linux/log2.h>
  34
  35static int pcpu_populate_chunk(struct pcpu_chunk *chunk,
  36                               int page_start, int page_end, gfp_t gfp)
  37{
  38        return 0;
  39}
  40
  41static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
  42                                  int page_start, int page_end)
  43{
  44        /* nada */
  45}
  46
  47static struct pcpu_chunk *pcpu_create_chunk(enum pcpu_chunk_type type,
  48                                            gfp_t gfp)
  49{
  50        const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
  51        struct pcpu_chunk *chunk;
  52        struct page *pages;
  53        unsigned long flags;
  54        int i;
  55
  56        chunk = pcpu_alloc_chunk(type, gfp);
  57        if (!chunk)
  58                return NULL;
  59
  60        pages = alloc_pages(gfp, order_base_2(nr_pages));
  61        if (!pages) {
  62                pcpu_free_chunk(chunk);
  63                return NULL;
  64        }
  65
  66        for (i = 0; i < nr_pages; i++)
  67                pcpu_set_page_chunk(nth_page(pages, i), chunk);
  68
  69        chunk->data = pages;
  70        chunk->base_addr = page_address(pages);
  71
  72        spin_lock_irqsave(&pcpu_lock, flags);
  73        pcpu_chunk_populated(chunk, 0, nr_pages);
  74        spin_unlock_irqrestore(&pcpu_lock, flags);
  75
  76        pcpu_stats_chunk_alloc();
  77        trace_percpu_create_chunk(chunk->base_addr);
  78
  79        return chunk;
  80}
  81
  82static void pcpu_destroy_chunk(struct pcpu_chunk *chunk)
  83{
  84        const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
  85
  86        if (!chunk)
  87                return;
  88
  89        pcpu_stats_chunk_dealloc();
  90        trace_percpu_destroy_chunk(chunk->base_addr);
  91
  92        if (chunk->data)
  93                __free_pages(chunk->data, order_base_2(nr_pages));
  94        pcpu_free_chunk(chunk);
  95}
  96
  97static struct page *pcpu_addr_to_page(void *addr)
  98{
  99        return virt_to_page(addr);
 100}
 101
 102static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai)
 103{
 104        size_t nr_pages, alloc_pages;
 105
 106        /* all units must be in a single group */
 107        if (ai->nr_groups != 1) {
 108                pr_crit("can't handle more than one group\n");
 109                return -EINVAL;
 110        }
 111
 112        nr_pages = (ai->groups[0].nr_units * ai->unit_size) >> PAGE_SHIFT;
 113        alloc_pages = roundup_pow_of_two(nr_pages);
 114
 115        if (alloc_pages > nr_pages)
 116                pr_warn("wasting %zu pages per chunk\n",
 117                        alloc_pages - nr_pages);
 118
 119        return 0;
 120}
 121