xref: /openbmc/linux/mm/percpu-km.c (revision ed84ef1c) 
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * mm/percpu-km.c - kernel memory based chunk allocation
4  *
5  * Copyright (C) 2010		SUSE Linux Products GmbH
6  * Copyright (C) 2010		Tejun Heo <tj@kernel.org>
7  *
8  * Chunks are allocated as a contiguous kernel memory using gfp
9  * allocation.  This is to be used on nommu architectures.
10  *
11  * To use percpu-km,
12  *
13  * - define CONFIG_NEED_PER_CPU_KM from the arch Kconfig.
14  *
15  * - CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK must not be defined.  It's
16  *   not compatible with PER_CPU_KM.  EMBED_FIRST_CHUNK should work
17  *   fine.
18  *
19  * - NUMA is not supported.  When setting up the first chunk,
20  *   @cpu_distance_fn should be NULL or report all CPUs to be nearer
21  *   than or at LOCAL_DISTANCE.
22  *
23  * - It's best if the chunk size is power of two multiple of
24  *   PAGE_SIZE.  Because each chunk is allocated as a contiguous
25  *   kernel memory block using alloc_pages(), memory will be wasted if
26  *   chunk size is not aligned.  percpu-km code will whine about it.
27  */
28 
29 #if defined(CONFIG_SMP) && defined(CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK)
30 #error "contiguous percpu allocation is incompatible with paged first chunk"
31 #endif
32 
33 #include <linux/log2.h>
34 
35 static void pcpu_post_unmap_tlb_flush(struct pcpu_chunk *chunk,
36 				      int page_start, int page_end)
37 {
38 	/* nothing */
39 }
40 
41 static int pcpu_populate_chunk(struct pcpu_chunk *chunk,
42 			       int page_start, int page_end, gfp_t gfp)
43 {
44 	return 0;
45 }
46 
47 static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
48 				  int page_start, int page_end)
49 {
50 	/* nada */
51 }
52 
53 static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
54 {
55 	const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
56 	struct pcpu_chunk *chunk;
57 	struct page *pages;
58 	unsigned long flags;
59 	int i;
60 
61 	chunk = pcpu_alloc_chunk(gfp);
62 	if (!chunk)
63 		return NULL;
64 
65 	pages = alloc_pages(gfp, order_base_2(nr_pages));
66 	if (!pages) {
67 		pcpu_free_chunk(chunk);
68 		return NULL;
69 	}
70 
71 	for (i = 0; i < nr_pages; i++)
72 		pcpu_set_page_chunk(nth_page(pages, i), chunk);
73 
74 	chunk->data = pages;
75 	chunk->base_addr = page_address(pages);
76 
77 	spin_lock_irqsave(&pcpu_lock, flags);
78 	pcpu_chunk_populated(chunk, 0, nr_pages);
79 	spin_unlock_irqrestore(&pcpu_lock, flags);
80 
81 	pcpu_stats_chunk_alloc();
82 	trace_percpu_create_chunk(chunk->base_addr);
83 
84 	return chunk;
85 }
86 
87 static void pcpu_destroy_chunk(struct pcpu_chunk *chunk)
88 {
89 	const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
90 
91 	if (!chunk)
92 		return;
93 
94 	pcpu_stats_chunk_dealloc();
95 	trace_percpu_destroy_chunk(chunk->base_addr);
96 
97 	if (chunk->data)
98 		__free_pages(chunk->data, order_base_2(nr_pages));
99 	pcpu_free_chunk(chunk);
100 }
101 
102 static struct page *pcpu_addr_to_page(void *addr)
103 {
104 	return virt_to_page(addr);
105 }
106 
107 static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai)
108 {
109 	size_t nr_pages, alloc_pages;
110 
111 	/* all units must be in a single group */
112 	if (ai->nr_groups != 1) {
113 		pr_crit("can't handle more than one group\n");
114 		return -EINVAL;
115 	}
116 
117 	nr_pages = (ai->groups[0].nr_units * ai->unit_size) >> PAGE_SHIFT;
118 	alloc_pages = roundup_pow_of_two(nr_pages);
119 
120 	if (alloc_pages > nr_pages)
121 		pr_warn("wasting %zu pages per chunk\n",
122 			alloc_pages - nr_pages);
123 
124 	return 0;
125 }
126 
127 static bool pcpu_should_reclaim_chunk(struct pcpu_chunk *chunk)
128 {
129 	return false;
130 }
131