mm/percpu-km.c

   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
  35 static int pcpu_populate_chunk(struct pcpu_chunk *chunk,
  36                                int page_start, int page_end, gfp_t gfp)
  37 {
  38         return 0;
  39 }
  40
  41 static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
  42                                   int page_start, int page_end)
  43 {
  44         /* nada */
  45 }
  46
  47 static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
  48 {
  49         const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
  50         struct pcpu_chunk *chunk;
  51         struct page *pages;
  52         unsigned long flags;
  53         int i;
  54
  55         chunk = pcpu_alloc_chunk(gfp);
  56         if (!chunk)
  57                 return NULL;
  58
  59         pages = alloc_pages(gfp, 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);
  70
  71         spin_lock_irqsave(&pcpu_lock, flags);
  72         pcpu_chunk_populated(chunk, 0, nr_pages);
  73         spin_unlock_irqrestore(&pcpu_lock, flags);
  74
  75         pcpu_stats_chunk_alloc();
  76         trace_percpu_create_chunk(chunk->base_addr);
  77
  78         return chunk;
  79 }
  80
  81 static void pcpu_destroy_chunk(struct pcpu_chunk *chunk)
  82 {
  83         const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
  84
  85         if (!chunk)
  86                 return;
  87
  88         pcpu_stats_chunk_dealloc();
  89         trace_percpu_destroy_chunk(chunk->base_addr);
  90
  91         if (chunk->data)
  92                 __free_pages(chunk->data, order_base_2(nr_pages));
  93         pcpu_free_chunk(chunk);
  94 }
  95
  96 static struct page *pcpu_addr_to_page(void *addr)
  97 {
  98         return virt_to_page(addr);
  99 }
 100
 101 static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai)
 102 {
 103         size_t nr_pages, alloc_pages;
 104
 105         /* all units must be in a single group */
 106         if (ai->nr_groups != 1) {
 107                 pr_crit("can't handle more than one group\n");
 108                 return -EINVAL;
 109         }
 110
 111         nr_pages = (ai->groups[0].nr_units * ai->unit_size) >> PAGE_SHIFT;
 112         alloc_pages = roundup_pow_of_two(nr_pages);
 113
 114         if (alloc_pages > nr_pages)
 115                 pr_warn("wasting %zu pages per chunk\n",
 116                         alloc_pages - nr_pages);
 117
 118         return 0;
 119 }