percpu-km.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * mm/percpu-km.c - kernel memory based chunk allocation
 *
 * Copyright (C) 2010		SUSE Linux Products GmbH
 * Copyright (C) 2010		Tejun Heo <tj@kernel.org>
 *
 * 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 void pcpu_post_unmap_tlb_flush(struct pcpu_chunk *chunk,
				      int page_start, int page_end)
{
	/* nothing */
}

static int pcpu_populate_chunk(struct pcpu_chunk *chunk,
			       int page_start, int page_end, gfp_t gfp)
{
	return 0;
}

static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
				  int page_start, int page_end)
{
	/* nada */
}

static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
{
	const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
	struct pcpu_chunk *chunk;
	struct page *pages;
	unsigned long flags;
	int i;

	chunk = pcpu_alloc_chunk(gfp);
	if (!chunk)
		return NULL;

	pages = alloc_pages(gfp, 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);

	spin_lock_irqsave(&pcpu_lock, flags);
	pcpu_chunk_populated(chunk, 0, nr_pages);
	spin_unlock_irqrestore(&pcpu_lock, flags);

	pcpu_stats_chunk_alloc();
	trace_percpu_create_chunk(chunk->base_addr);

	return chunk;
}

static void pcpu_destroy_chunk(struct pcpu_chunk *chunk)
{
	const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;

	if (!chunk)
		return;

	pcpu_stats_chunk_dealloc();
	trace_percpu_destroy_chunk(chunk->base_addr);

	if (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) {
		pr_crit("can't handle more than one group\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)
		pr_warn("wasting %zu pages per chunk\n",
			alloc_pages - nr_pages);

	return 0;
}

static bool pcpu_should_reclaim_chunk(struct pcpu_chunk *chunk)
{
	return false;
}