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;
}