percpu: implement kernel memory based chunk allocation

/*

 * 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.

 */

#ifdef 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)

{

	/* noop */

	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;

}

static struct page *pcpu_addr_to_page(void *addr);

static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai);

#ifdef CONFIG_NEED_PER_CPU_KM

#include "percpu-km.c"

#else

#include "percpu-vm.c"

#endif

/**

 * pcpu_chunk_addr_search - determine chunk containing specified address