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 void pcpu_post_unmap_tlb_flush(struct pcpu_chunk *chunk,
  36                                      int page_start, int page_end)
  37{
  38        /* nothing */
  39}
  40
  41static int pcpu_populate_chunk(struct pcpu_chunk *chunk,
  42                               int page_start, int page_end, gfp_t gfp)
  43{
  44        return 0;
  45}
  46
  47static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
  48                                  int page_start, int page_end)
  49{
  50        /* nada */
  51}
  52
  53static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
  54{
  55        const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
  56        struct pcpu_chunk *chunk;
  57        struct page *pages;
  58        unsigned long flags;
  59        int i;
  60
  61        chunk = pcpu_alloc_chunk(gfp);
  62        if (!chunk)
  63                return NULL;
  64
  65        pages = alloc_pages(gfp, order_base_2(nr_pages));
  66        if (!pages) {
  67                pcpu_free_chunk(chunk);
  68                return NULL;
  69        }
  70
  71        for (i = 0; i < nr_pages; i++)
  72                pcpu_set_page_chunk(nth_page(pages, i), chunk);
  73
  74        chunk->data = pages;
  75        chunk->base_addr = page_address(pages);
  76
  77        spin_lock_irqsave(&pcpu_lock, flags);
  78        pcpu_chunk_populated(chunk, 0, nr_pages);
  79        spin_unlock_irqrestore(&pcpu_lock, flags);
  80
  81        pcpu_stats_chunk_alloc();
  82        trace_percpu_create_chunk(chunk->base_addr);
  83
  84        return chunk;
  85}
  86
  87static void pcpu_destroy_chunk(struct pcpu_chunk *chunk)
  88{
  89        const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
  90
  91        if (!chunk)
  92                return;
  93
  94        pcpu_stats_chunk_dealloc();
  95        trace_percpu_destroy_chunk(chunk->base_addr);
  96
  97        if (chunk->data)
  98                __free_pages(chunk->data, order_base_2(nr_pages));
  99        pcpu_free_chunk(chunk);
 100}
 101
 102static struct page *pcpu_addr_to_page(void *addr)
 103{
 104        return virt_to_page(addr);
 105}
 106
 107static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai)
 108{
 109        size_t nr_pages, alloc_pages;
 110
 111        /* all units must be in a single group */
 112        if (ai->nr_groups != 1) {
 113                pr_crit("can't handle more than one group\n");
 114                return -EINVAL;
 115        }
 116
 117        nr_pages = (ai->groups[0].nr_units * ai->unit_size) >> PAGE_SHIFT;
 118        alloc_pages = roundup_pow_of_two(nr_pages);
 119
 120        if (alloc_pages > nr_pages)
 121                pr_warn("wasting %zu pages per chunk\n",
 122                        alloc_pages - nr_pages);
 123
 124        return 0;
 125}
 126
 127static bool pcpu_should_reclaim_chunk(struct pcpu_chunk *chunk)
 128{
 129        return false;
 130}
 131
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