percpu-km.c

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/*
 * mm/percpu-km.c - kernel memory based chunk allocation
 *
 * Copyright (C) 2010       SUSE Linux Products GmbH
 * Copyright (C) 2010       Tejun Heo <[email protected]>
 *
 * 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;
}