mm/percpu-km.c

   1 /*
   2  * mm/percpu-km.c - kernel memory based chunk allocation
   3  *
   4  * Copyright (C) 2010           SUSE Linux Products GmbH
   5  * Copyright (C) 2010           Tejun Heo <tj@kernel.org>
   6  *
   7  * This file is released under the GPLv2.
   8  *
   9  * Chunks are allocated as a contiguous kernel memory using gfp
  10  * allocation.  This is to be used on nommu architectures.
  11  *
  12  * To use percpu-km,
  13  *
  14  * - define CONFIG_NEED_PER_CPU_KM from the arch Kconfig.
  15  *
  16  * - CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK must not be defined.  It's
  17  *   not compatible with PER_CPU_KM.  EMBED_FIRST_CHUNK should work
  18  *   fine.
  19  *
  20  * - NUMA is not supported.  When setting up the first chunk,
  21  *   @cpu_distance_fn should be NULL or report all CPUs to be nearer
  22  *   than or at LOCAL_DISTANCE.
  23  *
  24  * - It's best if the chunk size is power of two multiple of
  25  *   PAGE_SIZE.  Because each chunk is allocated as a contiguous
  26  *   kernel memory block using alloc_pages(), memory will be wasted if
  27  *   chunk size is not aligned.  percpu-km code will whine about it.
  28  */
  29
  30 #if defined(CONFIG_SMP) && defined(CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK)
  31 #error "contiguous percpu allocation is incompatible with paged first chunk"
  32 #endif
  33
  34 #include <linux/log2.h>
  35
  36 static int pcpu_populate_chunk(struct pcpu_chunk *chunk,
  37                                int page_start, int page_end)
  38 {
  39         return 0;
  40 }
  41
  42 static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
  43                                   int page_start, int page_end)
  44 {
  45         /* nada */
  46 }
  47
  48 static struct pcpu_chunk *pcpu_create_chunk(void)
  49 {
  50         const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
  51         struct pcpu_chunk *chunk;
  52         struct page *pages;
  53         int i;
  54
  55         chunk = pcpu_alloc_chunk();
  56         if (!chunk)
  57                 return NULL;
  58
  59         pages = alloc_pages(GFP_KERNEL, order_base_2(nr_pages));
  60         if (!pages) {
  61                 pcpu_free_chunk(chunk);
  62                 return NULL;
  63         }
  64
  65         for (i = 0; i < nr_pages; i++)
  66                 pcpu_set_page_chunk(nth_page(pages, i), chunk);
  67
  68         chunk->data = pages;
  69         chunk->base_addr = page_address(pages) - pcpu_group_offsets[0];
  70
  71         spin_lock_irq(&pcpu_lock);
  72         pcpu_chunk_populated(chunk, 0, nr_pages);
  73         spin_unlock_irq(&pcpu_lock);
  74
  75         return chunk;
  76 }
  77
  78 static void pcpu_destroy_chunk(struct pcpu_chunk *chunk)
  79 {
  80         const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
  81
  82         if (chunk && chunk->data)
  83                 __free_pages(chunk->data, order_base_2(nr_pages));
  84         pcpu_free_chunk(chunk);
  85 }
  86
  87 static struct page *pcpu_addr_to_page(void *addr)
  88 {
  89         return virt_to_page(addr);
  90 }
  91
  92 static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai)
  93 {
  94         size_t nr_pages, alloc_pages;
  95
  96         /* all units must be in a single group */
  97         if (ai->nr_groups != 1) {
  98                 pr_crit("can't handle more than one group\n");
  99                 return -EINVAL;
 100         }
 101
 102         nr_pages = (ai->groups[0].nr_units * ai->unit_size) >> PAGE_SHIFT;
 103         alloc_pages = roundup_pow_of_two(nr_pages);
 104
 105         if (alloc_pages > nr_pages)
 106                 pr_warn("wasting %zu pages per chunk\n",
 107                         alloc_pages - nr_pages);
 108
 109         return 0;
 110 }