FreeBSD/Linux Kernel Cross Reference
sys/mm/percpu-km.c

     /*
      * mm/percpu-km.c - kernel memory based chunk allocation
      *
      * Copyright (C) 2010           SUSE Linux Products GmbH
      * Copyright (C) 2010           Tejun Heo <tj@kernel.org>
      *
      * This file is released under the GPLv2.
      *
      * Chunks are allocated as a contiguous kernel memory using gfp
     * allocation.  This is to be used on nommu architectures.
     *
     * To use percpu-km,
     *
     * - define CONFIG_NEED_PER_CPU_KM from the arch Kconfig.
     *
     * - CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK must not be defined.  It's
     *   not compatible with PER_CPU_KM.  EMBED_FIRST_CHUNK should work
     *   fine.
     *
     * - NUMA is not supported.  When setting up the first chunk,
     *   @cpu_distance_fn should be NULL or report all CPUs to be nearer
     *   than or at LOCAL_DISTANCE.
     *
     * - It's best if the chunk size is power of two multiple of
     *   PAGE_SIZE.  Because each chunk is allocated as a contiguous
     *   kernel memory block using alloc_pages(), memory will be wasted if
     *   chunk size is not aligned.  percpu-km code will whine about it.
     */
    
    #if defined(CONFIG_SMP) && defined(CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK)
    #error "contiguous percpu allocation is incompatible with paged first chunk"
    #endif
    
    #include <linux/log2.h>
    
    static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size)
    {
            unsigned int cpu;
    
            for_each_possible_cpu(cpu)
                    memset((void *)pcpu_chunk_addr(chunk, cpu, 0) + off, 0, size);
    
            return 0;
    }
    
    static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk, int off, int size)
    {
            /* nada */
    }
    
    static struct pcpu_chunk *pcpu_create_chunk(void)
    {
            const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
            struct pcpu_chunk *chunk;
            struct page *pages;
            int i;
    
            chunk = pcpu_alloc_chunk();
            if (!chunk)
                    return NULL;
    
            pages = alloc_pages(GFP_KERNEL, order_base_2(nr_pages));
            if (!pages) {
                    pcpu_free_chunk(chunk);
                    return NULL;
            }
    
            for (i = 0; i < nr_pages; i++)
                    pcpu_set_page_chunk(nth_page(pages, i), chunk);
    
            chunk->data = pages;
            chunk->base_addr = page_address(pages) - pcpu_group_offsets[0];
            return chunk;
    }
    
    static void pcpu_destroy_chunk(struct pcpu_chunk *chunk)
    {
            const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
    
            if (chunk && chunk->data)
                    __free_pages(chunk->data, order_base_2(nr_pages));
            pcpu_free_chunk(chunk);
    }
    
    static struct page *pcpu_addr_to_page(void *addr)
    {
            return virt_to_page(addr);
    }
    
    static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai)
    {
            size_t nr_pages, alloc_pages;
    
            /* all units must be in a single group */
            if (ai->nr_groups != 1) {
                    printk(KERN_CRIT "percpu: can't handle more than one groups\n");
                    return -EINVAL;
            }
    
           nr_pages = (ai->groups[0].nr_units * ai->unit_size) >> PAGE_SHIFT;
           alloc_pages = roundup_pow_of_two(nr_pages);
   
           if (alloc_pages > nr_pages)
                   printk(KERN_WARNING "percpu: wasting %zu pages per chunk\n",
                          alloc_pages - nr_pages);
   
           return 0;
   }

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