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1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _MM_SWAP_TABLE_H
3#define _MM_SWAP_TABLE_H
4
5#include <linux/rcupdate.h>
6#include <linux/atomic.h>
7#include "swap.h"
8
9/* A typical flat array in each cluster as swap table */
10struct swap_table {
11 atomic_long_t entries[SWAPFILE_CLUSTER];
12};
13
14/* For storing memcg private id */
15struct swap_memcg_table {
16 unsigned short id[SWAPFILE_CLUSTER];
17};
18
19#define SWP_TABLE_USE_PAGE (sizeof(struct swap_table) == PAGE_SIZE)
20
21/*
22 * A swap table entry represents the status of a swap slot on a swap
23 * (physical or virtual) device. The swap table in each cluster is a
24 * 1:1 map of the swap slots in this cluster.
25 *
26 * Swap table entry type and bits layouts:
27 *
28 * NULL: |---------------- 0 ---------------| - Free slot
29 * Shadow: |SWAP_COUNT|Z|---- SHADOW_VAL ---|1| - Swapped out slot
30 * PFN: |SWAP_COUNT|Z|------ PFN -------|10| - Cached slot
31 * Pointer: |----------- Pointer ----------|100| - (Unused)
32 * Bad: |------------- 1 -------------|1000| - Bad slot
33 *
34 * COUNT is `SWP_TB_COUNT_BITS` long, Z is the `SWP_TB_ZERO_FLAG` bit,
35 * and together they form the `SWP_TB_FLAGS_BITS` wide flags field.
36 * Each entry is an atomic long.
37 *
38 * Usages:
39 *
40 * - NULL: Swap slot is unused, could be allocated.
41 *
42 * - Shadow: Swap slot is used and not cached (usually swapped out). It reuses
43 * the XA_VALUE format to be compatible with working set shadows. SHADOW_VAL
44 * part might be all 0 if the working shadow info is absent. In such a case,
45 * we still want to keep the shadow format as a placeholder.
46 *
47 * Memcg ID is embedded in SHADOW_VAL.
48 *
49 * - PFN: Swap slot is in use, and cached. Memcg info is recorded on the page
50 * struct.
51 *
52 * - Pointer: Unused yet. `0b100` is reserved for potential pointer usage
53 * because only the lower three bits can be used as a marker for 8 bytes
54 * aligned pointers.
55 *
56 * - Bad: Swap slot is reserved, protects swap header or holes on swap devices.
57 */
58
59/* NULL Entry, all 0 */
60#define SWP_TB_NULL 0UL
61
62/* Swapped out: shadow */
63#define SWP_TB_SHADOW_MARK 0b1UL
64
65/* Cached: PFN */
66#define SWP_TB_PFN_BITS (SWAP_CACHE_PFN_BITS + SWAP_CACHE_PFN_MARK_BITS)
67#define SWP_TB_PFN_MARK 0b10UL
68#define SWP_TB_PFN_MARK_MASK (BIT(SWAP_CACHE_PFN_MARK_BITS) - 1)
69
70/* Flags: For PFN or shadow, contains SWAP_COUNT, width changes */
71#define SWP_TB_FLAGS_BITS min(5, BITS_PER_LONG - SWP_TB_PFN_BITS)
72#define SWP_TB_COUNT_BITS (SWP_TB_FLAGS_BITS - SWAP_TABLE_HAS_ZEROFLAG)
73#define SWP_TB_FLAGS_MASK (~((~0UL) >> SWP_TB_FLAGS_BITS))
74#define SWP_TB_COUNT_MASK (~((~0UL) >> SWP_TB_COUNT_BITS))
75#define SWP_TB_FLAGS_SHIFT (BITS_PER_LONG - SWP_TB_FLAGS_BITS)
76#define SWP_TB_COUNT_SHIFT (BITS_PER_LONG - SWP_TB_COUNT_BITS)
77#define SWP_TB_COUNT_MAX ((1 << SWP_TB_COUNT_BITS) - 1)
78/* The first flag is zero bit (SWAP_TABLE_HAS_ZEROFLAG) */
79#define SWP_TB_ZERO_FLAG BIT(BITS_PER_LONG - SWP_TB_FLAGS_BITS)
80
81/* Bad slot: ends with 0b1000 and rests of bits are all 1 */
82#define SWP_TB_BAD ((~0UL) << 3)
83
84/* Macro for shadow offset calculation */
85#define SWAP_COUNT_SHIFT SWP_TB_FLAGS_BITS
86
87/*
88 * Helpers for casting one type of info into a swap table entry.
89 */
90static inline unsigned long null_to_swp_tb(void)
91{
92 BUILD_BUG_ON(sizeof(unsigned long) != sizeof(atomic_long_t));
93 return 0;
94}
95
96static inline unsigned long __count_to_swp_tb(unsigned char count)
97{
98 /*
99 * At least three values are needed to distinguish free (0),
100 * used (count > 0 && count < SWP_TB_COUNT_MAX), and
101 * overflow (count == SWP_TB_COUNT_MAX).
102 */
103 BUILD_BUG_ON(SWP_TB_COUNT_BITS < SWAP_COUNT_MIN_BITS);
104 VM_WARN_ON(count > SWP_TB_COUNT_MAX);
105 return ((unsigned long)count) << SWP_TB_COUNT_SHIFT;
106}
107
108static inline unsigned long __flags_to_swp_tb(unsigned char flags)
109{
110 BUILD_BUG_ON(SWP_TB_FLAGS_BITS > BITS_PER_BYTE);
111 VM_WARN_ON(flags >> SWP_TB_FLAGS_BITS);
112 return ((unsigned long)flags) << SWP_TB_FLAGS_SHIFT;
113}
114
115static inline unsigned long pfn_to_swp_tb(unsigned long pfn, unsigned char flags)
116{
117 unsigned long swp_tb;
118
119 BUILD_BUG_ON(sizeof(unsigned long) != sizeof(void *));
120 BUILD_BUG_ON(SWAP_CACHE_PFN_BITS >
121 (BITS_PER_LONG - SWAP_CACHE_PFN_MARK_BITS - SWP_TB_FLAGS_BITS));
122
123 swp_tb = (pfn << SWAP_CACHE_PFN_MARK_BITS) | SWP_TB_PFN_MARK;
124 VM_WARN_ON_ONCE(swp_tb & SWP_TB_FLAGS_MASK);
125
126 return swp_tb | __flags_to_swp_tb(flags);
127}
128
129static inline unsigned long folio_to_swp_tb(struct folio *folio, unsigned char flags)
130{
131 return pfn_to_swp_tb(folio_pfn(folio), flags);
132}
133
134static inline unsigned long shadow_to_swp_tb(void *shadow, unsigned char flags)
135{
136 BUILD_BUG_ON((BITS_PER_XA_VALUE + 1) !=
137 BITS_PER_BYTE * sizeof(unsigned long));
138 BUILD_BUG_ON((unsigned long)xa_mk_value(0) != SWP_TB_SHADOW_MARK);
139
140 VM_WARN_ON_ONCE(shadow && !xa_is_value(shadow));
141 VM_WARN_ON_ONCE(shadow && ((unsigned long)shadow & SWP_TB_FLAGS_MASK));
142
143 return (unsigned long)shadow | SWP_TB_SHADOW_MARK | __flags_to_swp_tb(flags);
144}
145
146/*
147 * Helpers for swap table entry type checking.
148 */
149static inline bool swp_tb_is_null(unsigned long swp_tb)
150{
151 return !swp_tb;
152}
153
154static inline bool swp_tb_is_folio(unsigned long swp_tb)
155{
156 return ((swp_tb & SWP_TB_PFN_MARK_MASK) == SWP_TB_PFN_MARK);
157}
158
159static inline bool swp_tb_is_shadow(unsigned long swp_tb)
160{
161 return xa_is_value((void *)swp_tb);
162}
163
164static inline bool swp_tb_is_bad(unsigned long swp_tb)
165{
166 return swp_tb == SWP_TB_BAD;
167}
168
169static inline bool swp_tb_is_countable(unsigned long swp_tb)
170{
171 return (swp_tb_is_shadow(swp_tb) || swp_tb_is_folio(swp_tb) ||
172 swp_tb_is_null(swp_tb));
173}
174
175/*
176 * Helpers for retrieving info from swap table.
177 */
178static inline struct folio *swp_tb_to_folio(unsigned long swp_tb)
179{
180 VM_WARN_ON(!swp_tb_is_folio(swp_tb));
181 return pfn_folio((swp_tb & ~SWP_TB_FLAGS_MASK) >> SWAP_CACHE_PFN_MARK_BITS);
182}
183
184static inline void *swp_tb_to_shadow(unsigned long swp_tb)
185{
186 VM_WARN_ON(!swp_tb_is_shadow(swp_tb));
187 /* No shift needed, xa_value is stored as it is in the lower bits. */
188 return (void *)(swp_tb & ~SWP_TB_FLAGS_MASK);
189}
190
191static inline unsigned char __swp_tb_get_count(unsigned long swp_tb)
192{
193 VM_WARN_ON(!swp_tb_is_countable(swp_tb));
194 return ((swp_tb & SWP_TB_COUNT_MASK) >> SWP_TB_COUNT_SHIFT);
195}
196
197static inline unsigned char __swp_tb_get_flags(unsigned long swp_tb)
198{
199 VM_WARN_ON(!swp_tb_is_countable(swp_tb));
200 return ((swp_tb & SWP_TB_FLAGS_MASK) >> SWP_TB_FLAGS_SHIFT);
201}
202
203static inline int swp_tb_get_count(unsigned long swp_tb)
204{
205 if (swp_tb_is_countable(swp_tb))
206 return __swp_tb_get_count(swp_tb);
207 return -EINVAL;
208}
209
210static inline unsigned long __swp_tb_mk_count(unsigned long swp_tb, int count)
211{
212 return ((swp_tb & ~SWP_TB_COUNT_MASK) | __count_to_swp_tb(count));
213}
214
215/*
216 * Helpers for accessing or modifying the swap table of a cluster,
217 * the swap cluster must be locked.
218 */
219static inline void __swap_table_set(struct swap_cluster_info *ci,
220 unsigned int off, unsigned long swp_tb)
221{
222 atomic_long_t *table = rcu_dereference_protected(ci->table, true);
223
224 lockdep_assert_held(&ci->lock);
225 VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
226 atomic_long_set(&table[off], swp_tb);
227}
228
229static inline unsigned long __swap_table_xchg(struct swap_cluster_info *ci,
230 unsigned int off, unsigned long swp_tb)
231{
232 atomic_long_t *table = rcu_dereference_protected(ci->table, true);
233
234 lockdep_assert_held(&ci->lock);
235 VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
236 /* Ordering is guaranteed by cluster lock, relax */
237 return atomic_long_xchg_relaxed(&table[off], swp_tb);
238}
239
240static inline unsigned long __swap_table_get(struct swap_cluster_info *ci,
241 unsigned int off)
242{
243 atomic_long_t *table;
244
245 VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
246 table = rcu_dereference_check(ci->table, lockdep_is_held(&ci->lock));
247
248 return atomic_long_read(&table[off]);
249}
250
251static inline unsigned long swap_table_get(struct swap_cluster_info *ci,
252 unsigned int off)
253{
254 atomic_long_t *table;
255 unsigned long swp_tb;
256
257 VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
258
259 rcu_read_lock();
260 table = rcu_dereference(ci->table);
261 swp_tb = table ? atomic_long_read(&table[off]) : null_to_swp_tb();
262 rcu_read_unlock();
263
264 return swp_tb;
265}
266
267static inline void __swap_table_set_zero(struct swap_cluster_info *ci,
268 unsigned int ci_off)
269{
270#if SWAP_TABLE_HAS_ZEROFLAG
271 unsigned long swp_tb = __swap_table_get(ci, ci_off);
272
273 BUILD_BUG_ON(SWP_TB_ZERO_FLAG & ~SWP_TB_FLAGS_MASK);
274 VM_WARN_ON(!swp_tb_is_countable(swp_tb));
275 swp_tb |= SWP_TB_ZERO_FLAG;
276 __swap_table_set(ci, ci_off, swp_tb);
277#else
278 lockdep_assert_held(&ci->lock);
279 __set_bit(ci_off, ci->zero_bitmap);
280#endif
281}
282
283static inline bool __swap_table_test_zero(struct swap_cluster_info *ci,
284 unsigned int ci_off)
285{
286#if SWAP_TABLE_HAS_ZEROFLAG
287 unsigned long swp_tb = __swap_table_get(ci, ci_off);
288
289 VM_WARN_ON(!swp_tb_is_countable(swp_tb));
290 return !!(swp_tb & SWP_TB_ZERO_FLAG);
291#else
292 return test_bit(ci_off, ci->zero_bitmap);
293#endif
294}
295
296static inline void __swap_table_clear_zero(struct swap_cluster_info *ci,
297 unsigned int ci_off)
298{
299#if SWAP_TABLE_HAS_ZEROFLAG
300 unsigned long swp_tb = __swap_table_get(ci, ci_off);
301
302 VM_WARN_ON(!swp_tb_is_countable(swp_tb));
303 swp_tb &= ~SWP_TB_ZERO_FLAG;
304 __swap_table_set(ci, ci_off, swp_tb);
305#else
306 lockdep_assert_held(&ci->lock);
307 __clear_bit(ci_off, ci->zero_bitmap);
308#endif
309}
310
311#ifdef CONFIG_MEMCG
312static inline void __swap_cgroup_set(struct swap_cluster_info *ci,
313 unsigned int ci_off, unsigned long nr, unsigned short id)
314{
315 lockdep_assert_held(&ci->lock);
316 VM_WARN_ON_ONCE(ci_off >= SWAPFILE_CLUSTER);
317 if (WARN_ON_ONCE(!ci->memcg_table))
318 return;
319 do {
320 ci->memcg_table->id[ci_off++] = id;
321 } while (--nr);
322}
323
324static inline unsigned short __swap_cgroup_get(struct swap_cluster_info *ci,
325 unsigned int ci_off)
326{
327 lockdep_assert_held(&ci->lock);
328 VM_WARN_ON_ONCE(ci_off >= SWAPFILE_CLUSTER);
329 if (unlikely(!ci->memcg_table))
330 return 0;
331 return ci->memcg_table->id[ci_off];
332}
333
334static inline unsigned short __swap_cgroup_clear(struct swap_cluster_info *ci,
335 unsigned int ci_off,
336 unsigned long nr)
337{
338 unsigned short old = __swap_cgroup_get(ci, ci_off);
339
340 if (!old)
341 return 0;
342 do {
343 VM_WARN_ON_ONCE(ci->memcg_table->id[ci_off] != old);
344 ci->memcg_table->id[ci_off++] = 0;
345 } while (--nr);
346
347 return old;
348}
349#else
350static inline void __swap_cgroup_set(struct swap_cluster_info *ci,
351 unsigned int ci_off, unsigned long nr, unsigned short id)
352{
353}
354
355static inline unsigned short __swap_cgroup_get(struct swap_cluster_info *ci,
356 unsigned int ci_off)
357{
358 return 0;
359}
360
361static inline unsigned short __swap_cgroup_clear(struct swap_cluster_info *ci,
362 unsigned int ci_off,
363 unsigned long nr)
364{
365 return 0;
366}
367#endif
368
369#endif