1// SPDX-License-Identifier: GPL-2.0
2#include <linux/swap_cgroup.h>
3#include <linux/vmalloc.h>
4#include <linux/mm.h>
5
6#include <linux/swapops.h> /* depends on mm.h include */
7
8static DEFINE_MUTEX(swap_cgroup_mutex);
9struct swap_cgroup_ctrl {
10 struct page **map;
11 unsigned long length;
12 spinlock_t lock;
13};
14
15static struct swap_cgroup_ctrl swap_cgroup_ctrl[MAX_SWAPFILES];
16
17struct swap_cgroup {
18 unsigned short id;
19};
20#define SC_PER_PAGE (PAGE_SIZE/sizeof(struct swap_cgroup))
21
22/*
23 * SwapCgroup implements "lookup" and "exchange" operations.
24 * In typical usage, this swap_cgroup is accessed via memcg's charge/uncharge
25 * against SwapCache. At swap_free(), this is accessed directly from swap.
26 *
27 * This means,
28 * - we have no race in "exchange" when we're accessed via SwapCache because
29 * SwapCache(and its swp_entry) is under lock.
30 * - When called via swap_free(), there is no user of this entry and no race.
31 * Then, we don't need lock around "exchange".
32 *
33 * TODO: we can push these buffers out to HIGHMEM.
34 */
35
36/*
37 * allocate buffer for swap_cgroup.
38 */
39static int swap_cgroup_prepare(int type)
40{
41 struct page *page;
42 struct swap_cgroup_ctrl *ctrl;
43 unsigned long idx, max;
44
45 ctrl = &swap_cgroup_ctrl[type];
46
47 for (idx = 0; idx < ctrl->length; idx++) {
48 page = alloc_page(GFP_KERNEL | __GFP_ZERO);
49 if (!page)
50 goto not_enough_page;
51 ctrl->map[idx] = page;
52
53 if (!(idx % SWAP_CLUSTER_MAX))
54 cond_resched();
55 }
56 return 0;
57not_enough_page:
58 max = idx;
59 for (idx = 0; idx < max; idx++)
60 __free_page(ctrl->map[idx]);
61
62 return -ENOMEM;
63}
64
65static struct swap_cgroup *__lookup_swap_cgroup(struct swap_cgroup_ctrl *ctrl,
66 pgoff_t offset)
67{
68 struct page *mappage;
69 struct swap_cgroup *sc;
70
71 mappage = ctrl->map[offset / SC_PER_PAGE];
72 sc = page_address(mappage);
73 return sc + offset % SC_PER_PAGE;
74}
75
76static struct swap_cgroup *lookup_swap_cgroup(swp_entry_t ent,
77 struct swap_cgroup_ctrl **ctrlp)
78{
79 pgoff_t offset = swp_offset(ent);
80 struct swap_cgroup_ctrl *ctrl;
81
82 ctrl = &swap_cgroup_ctrl[swp_type(ent)];
83 if (ctrlp)
84 *ctrlp = ctrl;
85 return __lookup_swap_cgroup(ctrl, offset);
86}
87
88/**
89 * swap_cgroup_cmpxchg - cmpxchg mem_cgroup's id for this swp_entry.
90 * @ent: swap entry to be cmpxchged
91 * @old: old id
92 * @new: new id
93 *
94 * Returns old id at success, 0 at failure.
95 * (There is no mem_cgroup using 0 as its id)
96 */
97unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
98 unsigned short old, unsigned short new)
99{
100 struct swap_cgroup_ctrl *ctrl;
101 struct swap_cgroup *sc;
102 unsigned long flags;
103 unsigned short retval;
104
105 sc = lookup_swap_cgroup(ent, &ctrl);
106
107 spin_lock_irqsave(&ctrl->lock, flags);
108 retval = sc->id;
109 if (retval == old)
110 sc->id = new;
111 else
112 retval = 0;
113 spin_unlock_irqrestore(&ctrl->lock, flags);
114 return retval;
115}
116
117/**
118 * swap_cgroup_record - record mem_cgroup for a set of swap entries
119 * @ent: the first swap entry to be recorded into
120 * @id: mem_cgroup to be recorded
121 * @nr_ents: number of swap entries to be recorded
122 *
123 * Returns old value at success, 0 at failure.
124 * (Of course, old value can be 0.)
125 */
126unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id,
127 unsigned int nr_ents)
128{
129 struct swap_cgroup_ctrl *ctrl;
130 struct swap_cgroup *sc;
131 unsigned short old;
132 unsigned long flags;
133 pgoff_t offset = swp_offset(ent);
134 pgoff_t end = offset + nr_ents;
135
136 sc = lookup_swap_cgroup(ent, &ctrl);
137
138 spin_lock_irqsave(&ctrl->lock, flags);
139 old = sc->id;
140 for (;;) {
141 VM_BUG_ON(sc->id != old);
142 sc->id = id;
143 offset++;
144 if (offset == end)
145 break;
146 if (offset % SC_PER_PAGE)
147 sc++;
148 else
149 sc = __lookup_swap_cgroup(ctrl, offset);
150 }
151 spin_unlock_irqrestore(&ctrl->lock, flags);
152
153 return old;
154}
155
156/**
157 * lookup_swap_cgroup_id - lookup mem_cgroup id tied to swap entry
158 * @ent: swap entry to be looked up.
159 *
160 * Returns ID of mem_cgroup at success. 0 at failure. (0 is invalid ID)
161 */
162unsigned short lookup_swap_cgroup_id(swp_entry_t ent)
163{
164 return lookup_swap_cgroup(ent, NULL)->id;
165}
166
167int swap_cgroup_swapon(int type, unsigned long max_pages)
168{
169 void *array;
170 unsigned long array_size;
171 unsigned long length;
172 struct swap_cgroup_ctrl *ctrl;
173
174 if (!do_swap_account)
175 return 0;
176
177 length = DIV_ROUND_UP(max_pages, SC_PER_PAGE);
178 array_size = length * sizeof(void *);
179
180 array = vzalloc(array_size);
181 if (!array)
182 goto nomem;
183
184 ctrl = &swap_cgroup_ctrl[type];
185 mutex_lock(&swap_cgroup_mutex);
186 ctrl->length = length;
187 ctrl->map = array;
188 spin_lock_init(&ctrl->lock);
189 if (swap_cgroup_prepare(type)) {
190 /* memory shortage */
191 ctrl->map = NULL;
192 ctrl->length = 0;
193 mutex_unlock(&swap_cgroup_mutex);
194 vfree(array);
195 goto nomem;
196 }
197 mutex_unlock(&swap_cgroup_mutex);
198
199 return 0;
200nomem:
201 pr_info("couldn't allocate enough memory for swap_cgroup\n");
202 pr_info("swap_cgroup can be disabled by swapaccount=0 boot option\n");
203 return -ENOMEM;
204}
205
206void swap_cgroup_swapoff(int type)
207{
208 struct page **map;
209 unsigned long i, length;
210 struct swap_cgroup_ctrl *ctrl;
211
212 if (!do_swap_account)
213 return;
214
215 mutex_lock(&swap_cgroup_mutex);
216 ctrl = &swap_cgroup_ctrl[type];
217 map = ctrl->map;
218 length = ctrl->length;
219 ctrl->map = NULL;
220 ctrl->length = 0;
221 mutex_unlock(&swap_cgroup_mutex);
222
223 if (map) {
224 for (i = 0; i < length; i++) {
225 struct page *page = map[i];
226 if (page)
227 __free_page(page);
228 if (!(i % SWAP_CLUSTER_MAX))
229 cond_resched();
230 }
231 vfree(map);
232 }
233}
234